Perimeter L3 Switch Security Technical Implementation Guide

Using dedicated paths, the OOBM backbone connects the OOBM gateway routers located at the premise of the managed networks and at the NOC. Dedicated links can be deployed using provisioned circuits (ATM, Frame Relay, SONET, T-carrier, and others or VPN technologies such as subscribing to MPLS Layer 2 and Layer 3 VPN services) or implementing a secured path with gateway-to-gateway IPsec tunnel. The tunnel mode ensures that the management traffic will be logically separated from any other traffic traversing the same path.Information Assurance Officer

All network devices must present a DoD-approved warning banner prior to a system administrator logging on. The banner should warn any unauthorized user not to proceed. It also should provide clear and unequivocal notice to both authorized and unauthorized personnel that access to the device is subject to monitoring to detect unauthorized usage. Failure to display the required logon warning banner prior to logon attempts will limit DoD's ability to prosecute unauthorized access and also presents the potential to give rise to criminal and civil liability for systems administrators and information systems managers. In addition, DISA's ability to monitor the device's usage is limited unless a proper warning banner is displayed. DoD CIO has issued new, mandatory policy standardizing the wording of "notice and consent" banners and matching user agreements for all Secret and below DoD information systems, including stand-alone systems by releasing DoD CIO Memo, "Policy on Use of Department of Defense (DoD) Information Systems Standard Consent Banner and User Agreement", dated 9 May 2008. The banner is mandatory and deviations are not permitted except as authorized in writing by the Deputy Assistant Secretary of Defense for Information and Identity Assurance. Implementation of this banner verbiage is further directed to all DoD components for all DoD assets via USCYBERCOM CTO 08-008A.Information Assurance Officer

Terminating an idle session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled between the managed network device and a PC or terminal server when the later has been left unattended. In addition quickly terminating an idle session will also free up resources committed by the managed network device as well as reduce the risk of a management session from being hijacked. Setting the timeout of the session to 10 minutes or less increases the level of protection afforded critical network components.Information Assurance Officer

Detailed information about the network is sent across the network via SNMP. If this information is discovered by attackers it could be used to trace the network, show the networks topology, and possibly gain access to network devices.Information Assurance Officer

SNMP information can be used to trace the network and reveal networks topology that could enable malicious users to gain access to network devices.

Using ICMP messages for information gathering is a process allowing malicious computer attackers to launch attacks against a targeted network. In this stage the malicious attacker will try to determine what the characteristics of the targeted network. Techniques, such as host detection, service detection, network topology mapping, and operating system fingerprinting are often used. The data collected will be used to identify those hosts running network services, which may have a known vulnerability. This vulnerability may allow the malicious attacker to exploit vulnerabilities in the network or gain unauthorized access to those systems. This unauthorized access may become the focal point to the whole targeted network.Information Assurance OfficerECSC-1

Using ICMP messages for information gathering is a process allowing malicious computer attackers to launch attacks against a targeted network. In this stage the malicious attacker will try to determine what the characteristics of the targeted network. Techniques, such as host detection, service detection, network topology mapping, and operating system fingerprinting are often used. The data collected will be used to identify those hosts running network services, which may have a known vulnerability. This vulnerability may allow the malicious attacker to exploit vulnerabilities in the network or gain unauthorized access to those systems. This unauthorized access may become the focal point to the whole targeted network.Information Assurance OfficerECSC-1

A rogue router could send a fictitious routing update to convince a site's premise router to send traffic to an incorrect or even a rogue destination. This diverted traffic could be analyzed to learn confidential information of the site's network, or merely used to disrupt the network's ability to effectively communicate with other networks.Information Assurance OfficerECSC-1

Advertisement of routes by an autonomous system for networks that do not belong to any of its trusted peers pulls traffic away from the authorized network. This causes DoS on the network that allocated the block of addresses and may cause DoS on the network that is inadvertently advertising it as the originator. It is also possible that a misconfigured or compromised router within the network could re-distribute IGP routes into BGP thereby leaking internal routes.Information Assurance Officer

Numerous vulnerabilities exist with SNMP; therefore, without unique SNMP community names, the risk of compromise is dramatically increased. This is especially true with vendors default community names which are widely known by hackers and other networking experts. If a hacker gains access to these devices and can easily guess the name, this could result in denial of service, interception of sensitive information, or other destructive actions.Information Assurance Officer

By not restricting authorized accounts to their proper privilege level, access to restricted functions may be allowed before authorized personnel are trained or experienced enough to use those functions. Network disruptions or outages may occur due to mistakes made by inexperienced persons using accounts with greater privileges than necessary.Information Assurance Officer

A malicious user attempting to gain access to the network device may compromise an account that may be unauthorized for use. The unauthorized account may be a temporary or inactive account that is no longer needed to access the device. Denial of Service, interception of sensitive information, or other destructive actions could potentially take place if an unauthorized account is configured to access the network device.Information Assurance Officer

Administration and management connections performed across a network are inherently dangerous because anyone with a packet sniffer and access to the right LAN segment can acquire the network device account and password information. With this intercepted information they could gain access to the router and cause denial of service attacks, intercept sensitive information, or perform other destructive actions.Information Assurance Officer

Source routing is a feature of IP, whereby individual packets can specify routes. This feature is used in several different network attacks by bypassing perimeter and internal defense mechanisms.Information Assurance OfficerECSC-1

The Internet Control Message Protocol (ICMP) supports IP traffic by relaying information about paths, routes, and network conditions. Routers automatically send ICMP messages under a wide variety of conditions. Three ICMP messages are commonly used by attackers for network mapping and diagnosis: Host unreachable, Redirect, and Mask Reply.Information Assurance OfficerECSC-1

The additional services the router is enabled for increases the risk for an attack since the router will listen for these services. In addition, these services provide an unsecured method for an attacker to gain access to the router. Most recent software versions support remote configuration and monitoring using the World Wide Web's HTTP protocol. In general, HTTP access is equivalent to interactive access to the router. The authentication protocol used for HTTP is equivalent to sending a clear-text password across the network, and, unfortunately, there is no effective provision in HTTP for challenge-based or one-time passwords. This makes HTTP a relatively risky choice for use across the public Internet. Any additional services that are enabled increase the risk for an attack since the router will listen for these services. The HTTPS server may be enabled for administrative access.

Network devices not running the latest tested and approved versions of software are vulnerable to network attacks. Running the most current, approved version of system and device software helps the site maintain a stable base of security fixes and patches, as well as enhancements to IP security. Viruses, denial of service attacks, system weaknesses, back doors and other potentially harmful situations could render a system vulnerable, allowing unauthorized access to DoD assets.Information Assurance Officer

The TCP SYN attack involves transmitting a volume of connections that cannot be completed at the destination. This attack causes the connection queues to fill up, thereby denying service to legitimate TCP users.

Authentication for administrative access to the device is required at all times. A single account of last resort can be created on the device's local database for use in an emergency such as when the authentication server is down or connectivity between the device and the authentication server is not operable. The console or local account of last resort logon credentials must be stored in a sealed envelope and kept in a safe.

Terminating an idle session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been left unattended. In addition quickly terminating an idle session will also free up resources committed by the managed network device. Setting the timeout of the session to 10 minutes or less increases the level of protection afforded critical network components.Information Assurance Officer

Access lists are used to separate data traffic into that which it will route (permitted packets) and that which it will not route (denied packets). Secure configuration of routers makes use of access lists for restricting access to services on the router itself as well as for filtering traffic passing through the router. Inbound versus Outbound; it should be noted that some operating systems default access-lists are applied to the outbound queue. The more secure solution is to apply the access-list to the inbound queue for 3 reasons: •The router can protect itself before damage is inflicted. •The input port is still known, and can be filtered upon. •It is more efficient to filter packets before routing them. Information Assurance Officer

Enabling write access to the device via SNMP provides a mechanism that can be exploited by an attacker to set configuration variables that can disrupt network operations.Information Assurance Officer

In a VLAN-based network, switches use VLAN 1 as the default VLAN for in-band management and to communicate with other networking devices using Spanning-Tree Protocol (STP), Cisco Discovery Protocol (CDP), Dynamic Trunking Protocol (DTP), VLAN Trunking Protocol (VTP), and Port Aggregation Protocol (PAgP)--all untagged traffic. As a consequence, VLAN 1 may unwisely span the entire network if not appropriately pruned. If its scope is large enough, the risk of compromise can increase significantly.Information Assurance Officer

Unlike GRE (a simple encapsulating header) L2TP is a full-fledged communications protocol with control channel, data channels, and a robust command structure. In addition to PPP, other link layer types (called pseudowires) can be and are defined for delivery in L2TP by separate RFC documents. Further complexity is created by the capability to define vender-specific parameters beyond those defined in the L2TP specifications. The endpoint devices of an L2TP connection can be an L2TP Access Concentrator (LAC) in which case it inputs/outputs the layer 2 protocol to/from the L2TP tunnel. Otherwise it is an L2TP Network Server (LNS), in which case it inputs/outputs the layer 3 (IP) protocol to/from the L2TP tunnel. The specifications describe three reference models: LAC-LNS, LAC-LAC, and LNS-LNS, the first of which is the most common case. The LAC-LNS model allows a remote access user to reach his home network or ISP from a remote location. The remote access user either dials (or otherwise connects via layer 2) to a LAC device which tunnels his connection home to an awaiting LNS. The LAC could also be located on the remote user's laptop which connects to an LNS at home using some generic internet connection. The other reference models may be used for more obscure scenarios. Although the L2TP protocol does not contain encryption capability, it can be operated over IPSEC which would provide authentication and confidentiality. A remote user in the LAC-LNS model would most likely obtain a dynamically assigned IP address from the home network to ultimately use through the tunnel back to the home network. Secondly, the outer IP source address used to send the L2TP tunnel packet to the home network is likely to be unknown or highly variable. Thirdly, since the LNS provides the remote user with a dynamic IP address to use, the firewall at the home network would have to be dynamically updated to accept this address in conjunction with the outer tunnel address. Finally, there is also the issue of authentication of the remote user prior to divulging an acceptable IP address. As a result of all of these complications, the strict filtering rules applied to the IP-in-IP and GRE tunneling cases will likely not be possible in the L2TP scenario. In addition to the difficulty of enforcing addresses and endpoints (as explained above), the L2TP protocol itself is a security concern if allowed through a security boundary. In particular: 1) L2TP potentially allows link layer protocols to be delivered from afar. These protocols were intended for link-local scope only, are less defended, and not as well-known 2) The L2TP tunnels can carry IP packets that are very difficult to see and filter because of the additional layer 2 overhead 3) L2TP is highly complex and variable (vender-specific variability) and therefore would be a viable target that is difficult to defend. It is better left outside of the main firewall where less damage occurs if the L2TP-processing node is compromised. 4) Filtering cannot be used to detect and prevent other unintended layer 2 protocols from being tunneled. The strength of the application layer code would have to be relied on to achieve this task. 5) Regardless of whether the L2TP is handled inside or outside of the main network, a secondary layer of IP filtering is required, therefore bringing it inside doesn't save resources. Therefore, it is not recommended to allow unencrypted L2TP packets across the security boundary into the network's protected areas. Reference the Backbone Transport STIG for additional L2TP guidance and use.Information Assurance OfficerECSC-1

Double encapsulation can be initiated by an attacker who has access to a switch port belonging to the native VLAN of the trunk port. Knowing the victim's MAC address and with the victim attached to a different switch belonging to the same trunk group, thereby requiring the trunk link and frame tagging, the malicious user can begin the attack by sending frames with two sets of tags. The outer tag that will have the attacker's VLAN ID (probably the well-known and omnipresent VLAN 1) is stripped off by the switch, and the inner tag that will have the victim's VLAN ID is used by the switch as the next hop and sent out the trunk port.Information Assurance Officer

Remote administration is inherently dangerous because anyone with a sniffer and access to the right LAN segment could acquire the device account and password information. With this intercepted information they could gain access to the infrastructure and cause denial of service attacks, intercept sensitive information, or perform other destructive actions.

An attacker may attempt to connect to the device using SSH by guessing the authentication method, encryption algorithm, and keys. Limiting the amount of time allowed for authenticating and negotiating the SSH session reduces the window of opportunity for the malicious user attempting to make a connection to the network device.Information Assurance Officer

An attacker may attempt to connect to the device using SSH by guessing the authentication method and authentication key or shared secret. Setting the authentication retry to 3 or less strengthens against a Brute Force attack.Information Assurance Officer

VLAN hopping can be initiated by an attacker who has access to a switch port belonging to the same VLAN as the native VLAN of the trunk link connecting to another switch in which the victim is connected to. If the attacker knows the victim's MAC address, it can forge a frame with two 802.1q tags and a layer 2 header with the destination address of the victim. Since the frame will ingress the switch from a port belonging to its native VLAN, the trunk port connecting to victim's switch will simply remove the outer tag because native VLAN traffic is to be untagged. The switch will forward the frame unto the trunk link unaware of the inner tag with a VLAN ID for which the victim's switchport is a member of.Information Assurance Officer

Double encapsulation can be initiated by an attacker who has access to a switch port belonging to the native VLAN of the trunk port. Knowing the victims MAC address and with the victim attached to a different switch belonging to the same trunk group, thereby requiring the trunk link and frame tagging, the malicious user can begin the attack by sending frames with two sets of tags. The outer tag that will have the attackers VLAN ID (probably the well-known and omnipresent VLAN 1) is stripped off by the switch, and the inner tag that will have the victims VLAN ID is used by the switch as the next hop and sent out the trunk port.Information Assurance Officer

All ports, including the internal sc0 interface, are configured by default to be members of VLAN 1. In a VLAN-based network, switches use VLAN 1 as the default VLAN for in-band management and to communicate with other networking devices using Spanning-Tree Protocol (STP), Cisco Discovery Protocol (CDP), Dynamic Trunking Protocol (DTP), VLAN Trunking Protocol (VTP), and Port Aggregation Protocol (PAgP) all untagged traffic. As a consequence, VLAN 1 may unwisely span the entire network if not appropriately pruned. If its scope is large enough, the risk of compromise can increase significantly.Information Assurance Officer

A TCP connection consists of a three-way handshake message sequence. A connection request is transmitted by the originator, an acknowledgement is returned from the receiver, and then an acceptance of that acknowledgement is sent by the originator. An attacker's goal in this scenario is to cause a denial of service to the network or device by initiating a high volume of TCP packets, then never sending an acknowledgement, leaving connections in a half-opened state. Without the device having a connection or time threshold for these half-opened sessions, the device risks being a victim of a denial of service attack. Setting a TCP timeout threshold will instruct the device to shut down any incomplete connections. Services such as SSH, BGP, SNMP, LDP, etc. are some services that may be prone to these types of denial of service attacks. If the router does not have any BGP connections with BGP neighbors across WAN links, values could be set to even tighter constraints.Information Assurance Officer

Vulnerability assessments must be reviewed by the SA and protocols must be approved by the IA staff before entering the enclave. Access Control Lists (ACLs) are the first line of defense in a layered security approach. They permit authorized packets and deny unauthorized packets based on port or service type. They enhance the posture of the network by not allowing packets to even reach a potential target within the security domain. The list provided are highly susceptible ports and services that should be blocked or limited as much as possible without adversely affecting customer requirements. Auditing packets attempting to penetrate the network but are stopped by an ACL will allow network administrators to broaden their protective ring and more tightly define the scope of operation. If the perimeter is in a Deny-by-Default posture and what is allowed through the filter is IAW DoD Instruction 8551.1, and if the permit rule is explicitly defined with explicit ports and protocols allowed, then all requirements related to PPS being blocked would be satisfied. Information Assurance Officer

The enclave perimeter requirement for filtering, to include JTF-GNO PPS filtering rules, and monitoring traffic will be enforced for any traffic from the AG. All traffic entering the enclave from the AG must enter through the firewall and be monitored by internal IDS. All traffic leaving the enclave, regardless of the destination--AG or NIPRNet addresses, will be filtered by the premise router's egress filter to verify that the source IP address belongs to the enclave.

Many of the known attacks in stateless autoconfiguration are defined in RFC 3756 were present in IPv4 ARP attacks. IPSec AH was originally suggested as mitigation for the link local attacks, but has since been found to have bootstrapping problems and to be very administrative intensive. Due to first requiring an IP address in order to set up the IPSec security association creates the chicken-before-the-egg dilemma. There are solutions being developed (Secure Neighbor Discovery and Cryptographic Generated Addressing) to secure these threats but are not currently available at the time of this writing. To mitigate these vulnerabilities, links that have no hosts connected such as the interface connecting to external gateways will be configured to suppress router advertisements. Disable (or do not configure) all IPv6 Neighbor Discovery functions across tunnels including the Neighbor Unreachability Detection (NUD) function. Note: this is applicable only when the inner IP layer is IPv6 since IPv4 does not have the Neighbor Discovery functionality.Information Assurance OfficerDCBP-1, ECSC-1

If the same passwords are used between eBGP neighbors, the chance of a hacker compromising any of the BGP sessions increases. It is possible that a malicious user exists in one autonomous system who would know the password used for the eBGP session. This user would then be able to hijack BGP sessions with other trusted neighbors.Information Assurance OfficerECSC-1

The additional services enabled on a router increases the risk for an attack since the router will listen for these services. In addition, these services provide an unsecured method for an attacker to gain access to the router.Information Assurance Officer

Berkeley Software Distribution (BSD) "r" commands allow users to execute commands on remote systems using a variety of protocols. The BSD "r" commands (e.g., rsh, rlogin, rcp, rdump, rrestore, and rdist) are designed to provide convenient remote access without passwords to services such as remote command execution (rsh), remote login (rlogin), and remote file copy (rcp and rdist). The difficulty with these commands is they use address-based authentication. An attacker who convinces a server that he is coming from a "trusted" machine can essentially get complete and unrestricted access to a system. The attacker can convince the server by impersonating a trusted machine and using IP address, by confusing DNS so that DNS thinks that the attacker's IP address maps to a trusted machine's name, or by any of a number of other methods.Information Assurance Officer

The Internet Control Message Protocol version 6 (ICMPv6) supports IPv6 traffic by relaying information about paths, routes, and network conditions. Routers automatically send ICMPv6 messages under a wide variety of conditions. ICMPv6 messages are commonly used by attackers for network mapping and diagnosis: Host unreachable, and Redirect.Information Assurance Officer

Since NTP is used to ensure accurate log file time stamp information, NTP could pose a security risk if a malicious user were able to falsify NTP information. To launch an attack on the NTP infrastructure, a hacker could inject time that would be accepted by NTP clients by spoofing the IP address of a valid NTP server. To mitigate this risk, the time messages must be authenticated by the client before accepting them as a time source. Two NTP-enabled devices can communicate in either client-server mode or peer-to-peer mode (aka "symmetric mode"). The peering mode is configured manually on the device and indicated in the outgoing NTP packets. The fundamental difference is the synchronization behavior: an NTP server can synchronize to a peer with better stratum, whereas it will never synchronize to its client regardless of the client's stratum. From a protocol perspective, NTP clients are no different from the NTP servers. The NTP client can synchronize to multiple NTP servers, select the best server and synchronize with it, or synchronize to the averaged value returned by the servers. A hierarchical model can be used to improve scalability. With this implementation, an NTP client can also become an NTP server providing time to downstream clients at a higher stratum level and of decreasing accuracy than that of its upstream server. To increase availability, NTP peering can be used between NTP servers. In the event the device loses connectivity to its upstream NTP server, it will be able to choose time from one of its peers. The NTP authentication model is opposite of the typical client-server authentication model. NTP authentication enables an NTP client or peer to authenticate time received from their servers and peers. It is not used to authenticate NTP clients because NTP servers do not care about the authenticity of their clients, as they never accept any time from them.

One of the fragmentation weaknesses known in IPv6 is the undetermined transport packet. This is a packet that contains an undetermined protocol due to fragmentation. Depending on the length of the IPv6 extension header chain, the initial fragment may not contain the layer four port information of the packet.Information Assurance Officer

The Routing header is used by an IPv6 source to specify a list of intermediate nodes that a packet has to traverse on the path to its destination. If the packet cannot take the path, it is returned to the source node in an ICMPv6 unreachable error message. This header supports a function very similar to the IPv4 packet Loose Source Routing. The routing header can be used maliciously to send a packet through a path where less robust security is in place, than through the presumably preferred path by routing protocols. Use of the routing extension header has few legitimate uses other than as implemented by Mobile IPv6. The Routing header is identified by a Next Header value of 43 and should be filtered by type using an ACL. The Type 0 Routing Header (RFC 5095) is dangerous because it allows attackers to spoof source addresses and get traffic in response, rather than to the real owner of the address. Secondly, a packet with an allowed destination address could be sent through a Firewall only to bounce to a different node once inside using the Routing Header functionality. If the Type 0 Routing Header must be used, it must be used in conjunction with either the IPsec AH or the IPsec Encapsulation Security Payload (ESP) headers. The Routing Header is identified by a Next Header value of 43 (0x2B) and can be filtered by type using an ACL similar to: deny ipv6 any routing-type 0 log. The Type 1 Routing Header is defined by an abandoned specification called “Nimrod Routing”. Assuming that most implementations will not recognize the Type 1 Routing Header, it must be dropped. When IETF standards explicitly require nodes to gracefully rejected invalid or deprecated options, in the case of Routing Headers, however, under certain conditions the specification allows a node to “ignore the Routing Header and proceed to the next header in the packet” [RFC 2460, section 4.4 para 2]. This allows a spurious data channel of arbitrary size and must not be allowed. The Type 3 through 255 Routing Header values in the routing type field are currently undefined and should also be dropped inbound and outbound. The Routing Header is identified by a Next Header value of 43 (0x2B). To drop all types including type 2 Mobile IPv6 (MIPv6) a filter can be defined to drop the Routing Header 43 (0x2B). If MIPv6 is required a permit will be required for Routing Header 43 (0x2B) Type 2, and then drop the remaining Routing Headers 43 (0x2B).

Scanning will usually be the major stage of an information gathering process a malicious computer attacker will launch against a targeted network. With this stage the malicious computer attacker will try to determine what the characteristics of the targeted network are. Techniques, such as host detection, service detection, network topology mapping, and operating system fingerprinting are often used. The data collected will be used to identify those Hosts (if any) that are running a network service, which may have a known vulnerability. This vulnerability may allow the malicious computer attacker to execute a remote exploit in order to gain unauthorized access to those systems. This unauthorized access may become the focal point to the whole targeted network.Information Assurance Officer

Scanning will usually be the major stage of an information gathering process a malicious computer attacker will lunch against a targeted network. With this stage the malicious computer attacker will try to determine what the characteristics of the targeted network are. Techniques, such as host detection, service detection, network topology mapping, and operating system fingerprinting are often used. The data collected will be used to identify those Hosts (if any) that are running a network service, which may have a known vulnerability. This vulnerability may allow the malicious computer attacker to execute a remote exploit in order to gain unauthorized access to those systems. This unauthorized access may become the focal point to the whole targeted network.

Access lists are used to separate data traffic into that which it will route (permitted packets) and that which it will not route (denied packets). Secure configuration of routers makes use of access lists for restricting access to services on the router itself as well as for filtering traffic passing through the router. Inbound versus Outbound; it should be noted that some operating systems default access-lists are applied to the outbound queue. The more secure solution is to apply the access-list to the inbound queue for 3 reasons: • The router can protect itself before damage is inflicted. • The input port is still known, and can be filtered upon. • It is more efficient to filter packets before routing them. Information Assurance Officer

As currently defined, site local addresses are ambiguous and can be present in multiple sites. The address itself does not contain any indication of the site to which it belongs. The use of site-local addresses has the potential to adversely affect network security through leaks, ambiguity and potential misrouting, as documented in section 2 of RFC3879. RFC3879 formally deprecates the IPv6 site-local unicast prefix defined in RFC3513, i.e., 1111111011 binary or FEC0::/10.Information Assurance OfficerECSC-1

IPv6 multicast addresses should never be a source address. They should only be destination addresses.Information Assurance Officer

The IPv6 transition mechanisms include a technique for hosts and routers to dynamically tunnel IPv6 packets over IPv4 routing infrastructure. IPv6 nodes that use this technique are assigned special IPv6 unicast addresses that carry a global IPv4 address in the low-order 32 bits. IPv4-compatible IPv6 addresses should never appear as a source or destination address. These addresses begin with 0000 and have ‘0000’ in the 16 bit field preceding the IPv4 address. RFC 4291 deprecated the IPv4-compatible addresses.Information Assurance Officer

The IPv6 transition mechanisms include a technique for hosts and routers to dynamically tunnel IPv6 packets over IPv4 routing infrastructure. IPv6 nodes that use this technique are assigned special IPv6 unicast addresses that carry a global IPv4 address in the low-order 32 bits. IPv4-mapped IPv6 addresses should never appear as a source or destination address. These addresses begin with 0000 and have ‘FFFF’ in the 16 bit field preceding the IPv4 address. There is little use for the IPv4-mapped addresses and there has been some confusion for what their intended use was. There were three revisions of IPv6 Basic API specification (RFC 2133, 2553, and 3493). Under the current usage of the API, no packets should appear on the wire with these addresses so blocking them is the policy.Information Assurance Officer

The IANA has assigned the FC00::/7 prefix to Unique Local Unicast addresses. Unique Local Address (ULA) is a routable address that is not intended to be on the Internet. Site border routers and firewalls should be configured to block any packets with ULA source or destination addresses outside of the site. This will ensure that packets with Local IPv6 destination addresses will not be forwarded outside of the site via a default route. Drop all inbound IPv6 packets with an address FC00::/7 as its source address. Note that includes any address beginning with FC or FD. Information Assurance OfficerECSC-1

Unicast Reverse Path Forwarding (uRPF) provides a mechanism for IP address spoof protection. When uRPF is enabled on an interface, the router examines all packets received as input on that interface to make sure that the source address and source interface appear in the routing table and match the interface on which the packet was received. If the packet was received from one of the best reverse path routes, the packet is forwarded as normal. If there is no reverse path route on the same interface from which the packet was received, it might mean that the source address was modified. If Unicast RPF does not find a reverse path for the packet, the packet is dropped. If internal nodes automatically configure an address based on a prefix from a bogus Router Advertisement a dangerous situation may exist. An internal host may contact an internal server which responds with a packet that could be routed outside of the network via default routing (because the routers do not recognize the destination address as an internal address). To prevent this, filtering should be applied to network interfaces between internal host LANs and internal server LANs to insure that source addresses have valid prefixes. Information Assurance Officer

SSH Version 1 is a protocol that has never been defined in a standard. Since SSH-1 has inherent design flaws which make it vulnerable to attacks, e.g., man-in-the-middle attacks, it is now generally considered obsolete and should be avoided by explicitly disabling fallback to SSH-1.Information Assurance Officer

ISATAP is an automatic tunnel mechanism that does not provide authentication such as IPSec. As a result of this limitation, ISATAP is thought of as a tool that is used inside the enclave among trusted hosts, which would limit it to internal attacks. ISATAP is a service versus a product, and is readily available to most users. If a user knows the ISATAP router IP address, they can essentially get onto the IPv6 intranet. To control the vulnerability of this tunnel mechanism, it is critical to control the use of protocol 41 and use IPv4 filters to control what IPv4 nodes can send protocol 41 packets to an ISATAP router interface. Although the ISATAP tunneling mechanism is similar to other automatic tunneling mechanisms, such as IPv6 6to4 tunneling, ISATAP is designed for transporting IPv6 packets between sites within an enclave, not between enclaves.Information Assurance OfficerECSC-1

6to4 is an automated tunneling mechanism that provides v6 capability to a dual-stack node or v6 capable site that has only IPv4 connectivity to the site. One key difference between automatic 6to4 tunnels and manually configured tunnels is that the tunnel is not point-to-point; it is point-to-multipoint. Basic 6to4 implementation can be used to connect single nodes too. In 6to4 tunnel implementations, tunnels are not defined in pairs as in manual tunnels. The tunnel destination is determined by the IPv4 address of the border router extracted from the IPv6 address that starts with the prefix 2002::/16, where the format is 2002:IPv4-address in hex::/48. 6to4 traffic takes an asymmetric routing path, outbound traffic and return traffic may take different paths. Although the 6to4 site can select the relay it wants to use, it has no control of the return relay used. See diagram in the STIG. Ensuring reliable operations from relays and knowing who is managing the relay are important and are concerns to preventing against denial of service attacks. 6to4 site routers are not capable of identifying bogus traffic injected from malicious 6to4 relay manufacturing packets. Specifying the exact IPv4 address of the 6to4 relay on the 6to4 router can mitigate these vulnerabilities. 6to4 tunnels are required to discard unexpected protocol 41 packets and inspect IPv6 traffic at the decapsulator end-point. Information Assurance Officer

Network Address Translation with Protocol Translation (NAT-PT), defined in [RFC2766], is a service that can be used to translate data sent between IP-heterogeneous nodes. NAT-PT translates a IPv4 datagram into a semantically equivalent IPv6 datagram or vice versa. For this service to work it has to be located in the connection point between the IPv4 network and the IPv6 network. The PT-part of the NAT-PT handles the interpretation and translation of the semantically equivalent IP header, either from IPv4 to IPv6 or from IPv6 to IPv4. Like NAT, NATPT also uses a pool of addresses which it dynamically assigns to the translated datagrams. The NAT-PT architecture is not one of the preferred DoD IPv6 transition paradigms due to the deprecation of NAT-PT within the DoD community. However, as described in the "DoD IPv6 Guidance for Information Assurance (IA) Milestone Objective 3 (MO3) Requirements, some services/agencies may chose to implement this transition mechanism within an enclave. The following sub-sections provide guidelines for the use of NAT-PT within a controlled enclave. In addition to the single point of failure, the reduced performance of an application level gateway, coupled with limitations on the kinds of applications that work, decreases the overall value and utility of the network. NAT-PT also inhibits the ability to deploy security at the IP layer. Information Assurance Officer

Network Address Translation with Protocol Translation (NAT-PT), defined in [RFC2766], is a service that can be used to translate data sent between IP-heterogeneous nodes. NAT-PT translates IPv4 datagrams into a semantically equivalent IPv6 datagram or vice versa. For this service to work it has to be located in the connection point between the IPv4 network and the IPv6 network. The PT-part of the NAT-PT handles the interpretation and translation of the semantically equivalent IP header, either from IPv4 to IPv6 or from IPv6 to IPv4. Like NAT, NATPT also uses a pool of addresses which it dynamically assigns to the translated datagrams. The NAT-PT architecture is not one of the preferred DoD IPv6 transition paradigms due to the deprecation of NAT-PT within the DoD community. However, as described in the "DoD IPv6 Guidance for Information Assurance (IA) Milestone Objective 3 (MO3) Requirements, some services/agencies may choose to implement this transition mechanism within an enclave. The following sub-sections provide guidelines for the use of NAT-PT within a controlled enclave. In addition to the single point of failure, the reduced performance of an application level gateway, coupled with limitations on the kinds of applications that work, decreases the overall value and utility of the network. NAT-PT also inhibits the ability to deploy security at the IP layer.Information Assurance OfficerECSC-1

The use of Authentication, Authorization, and Accounting (AAA) affords the best methods for controlling user access, authorization levels, and activity logging. By enabling AAA on the routers in conjunction with an authentication server such as TACACS+ or RADIUS, the administrators can easily add or remove user accounts, add or remove command authorizations, and maintain a log of user activity. The use of an authentication server provides the capability to assign router administrators to tiered groups that contain their privilege level that is used for authorization of specific commands. For example, user mode would be authorized for all authenticated administrators while configuration or edit mode should only be granted to those administrators that are permitted to implement router configuration changes.Information Assurance Officer

The Out-of-Band Management (OOBM) network is an IP network used exclusively for the transport of OAM&P data from the network being managed to the OSS components located at the NOC. Its design provides connectivity to each managed network device enabling network management traffic to flow between the managed NEs and the NOC. This allows the use of paths separate from those used by the network being managed. Traffic from the managed network to the management network and vice-versa must be secured via IPSec encapsulation.Information Assurance Officer

The IPSec tunnel end points may be configured on the OOBM gateway routers connecting the managed network and the NOC. They may also be configured on a firewall or VPN concentrator located behind the gateway router. In either case, the crypto access-list used to identify the traffic to be protected must be a mirror (both IP source and destination address) of the crypto access list configured at the remote VPN peer.System AdministratorInformation Assurance Officer

If the gateway router is not a dedicated device for the OOBM network, several safeguards must be implemented for containment of management and production traffic boundaries. Since the managed network and the management network are separate routing domains, separate IGP routing instances must be configured on the router—one for the managed network and one for the OOBM network. System AdministratorECSC-1

If the gateway router is not a dedicated device for the OOBM network, several safeguards must be implemented for containment of management and production traffic boundaries. Since the managed network and the management network are separate routing domains, separate IGP routing instances must be configured on the router—one for the managed network and one for the OOBM network. In addition, the routes from the two domains must not be redistributed to each other. System AdministratorInformation Assurance OfficerECSC-1

If the gateway router is not a dedicated device for the OOBM network, several safeguards must be implemented for containment of management and production traffic boundaries. It is imperative that hosts from the managed network are not able to access the OOBM gateway router.System AdministratorInformation Assurance Officer

If the gateway router is not a dedicated device for the OOBM network, several safeguards must be implemented for containment of management and production traffic boundaries such as using interface ACLs or filters at the boundaries between the two networks. System AdministratorInformation Assurance OfficerECSC-1

If the gateway router is not a dedicated device for the OOBM network, several safeguards must be implemented for containment of management and production traffic boundaries. To provide separation, access control lists or filters must be configured to block any traffic from the management network destined for the managed network's production address spaces.System AdministratorInformation Assurance Officer

The OOBM access switch will connect to the management interface of the managed network device. The management interface of the managed network device will be directly connected to the OOBM network. An OOBM interface does not forward transit traffic; thereby, providing complete separation of production and management traffic. Since all management traffic is immediately forwarded into the management network, it is not exposed to possible tampering. The separation also ensures that congestion or failures in the managed network do not affect the management of the device. If the OOBM interface does not have an IP address from the managed network address space, it will not have reachability from the NOC using scalable and normal control plane and forwarding mechanisms.System AdministratorInformation Assurance Officer

The OOBM access switch will connect to the management interface of the managed network device. The management interface can be a true OOBM interface or a standard interface functioning as the management interface. In either case, the management interface of the managed network device will be directly connected to the OOBM network. An OOBM interface does not forward transit traffic; thereby, providing complete separation of production and management traffic. Since all management traffic is immediately forwarded into the management network, it is not exposed to possible tampering. The separation also ensures that congestion or failures in the managed network do not affect the management of the device. If the device does not have an OOBM port, the interface functioning as the management interface must be configured so that management traffic does not leak into the managed network and that production traffic does not leak into the management network.System AdministratorInformation Assurance Officer

The OOBM access switch will connect to the management interface of the managed network elements. The management interface can be a true OOBM interface or a standard interface functioning as the management interface. In either case, the management interface of the managed network element will be directly connected to the OOBM network. If the device does not have an OOBM port, the interface functioning as the management interface must be configured so that management traffic does not leak into the managed network and that production traffic does not leak into the management network.System AdministratorInformation Assurance OfficerECSC-1

The OOBM access switch will connect to the management interface of the managed network elements. The management interface can be a true OOBM interface or a standard interface functioning as the management interface. In either case, the management interface of the managed network element will be directly connected to the OOBM network. An OOBM interface does not forward transit traffic; thereby, providing complete separation of production and management traffic. Since all management traffic is immediately forwarded into the management network, it is not exposed to possible tampering. The separation also ensures that congestion or failures in the managed network do not affect the management of the device. System AdministratorECSC-1

The management network must still have its own subnet in order to enforce control and access boundaries provided by Layer 3 network nodes such as routers and firewalls. Management traffic between the managed network elements and the management network is routed via the same links and nodes as that used for production or operational traffic. Safeguards must be implemented to ensure that the management traffic does not leak past the managed network’s premise equipment such as using egress ACLs.System AdministratorInformation Assurance OfficerECSC-1

If the management systems reside within the same layer 2 switching domain as the managed network device, then separate VLANs will be deployed to provide separation at that level. In this case, the management network still has its own subnet while at the same time it is defined as a unique VLAN.System AdministratorInformation Assurance Officer

If the management systems reside within the same Layer 2 switching domain as the managed network elements, then separate VLANs will be deployed to provide separation at that level. In this case, the management network still has its own subnet while at the same time it is defined as a unique VLAN. Inter-VLAN routing or the routing of traffic between nodes residing in different subnets requires a router or multi-layer switch (MLS). Access control lists must be used to enforce the boundaries between the management network and the network being managed. When using a MLS, an alternate method to prevent inter-VLAN routing is to configure the management Virtual Routing and Forwarding (VRF) to not import route targets from other VRFs which would ensure there is no reachability between networks.

If the management systems reside within the same layer 2 switching domain as the managed network elements, then separate VLANs will be deployed to provide separation at that level. In this case, the management network still has its own subnet while at the same time it is defined as a unique VLAN. Inter-VLAN routing or the routing of traffic between nodes residing in different subnets requires a router or multi-layer switch (MLS). Access control lists must be used to enforce the boundaries between the management network and the network being managed. All physical and virtual (i.e. MLS SVI) routed interfaces must be configured with ACLs to prevent the leaking of unauthorized traffic from one network to the other. System AdministratorInformation Assurance Officer

Similar to the OOBM model, when the production network is managed in-band, the management network could also be housed at a NOC that is located locally or remotely at a single or multiple interconnected sites. NOC interconnectivity as well as connectivity between the NOC and the managed networks’ premise routers would be enabled using either provisioned circuits or VPN technologies such as IPSec tunnels or MPLS VPN services. System AdministratorInformation Assurance OfficerECSC-1

Protecting data sitting in a server VLAN is necessary and can be accomplished using access control lists on VLANs provisioned for servers. Without proper access control of traffic entering or leaving the server VLAN, potential threats such as a denial of service, data corruption, or theft could occur, resulting in the inability to complete mission requirements by authorized users.Information Assurance Officer

ACLs on VLAN interfaces do not protect against compromised servers. The Server farm vlans need to protect the servers located on one subnet from servers located on another subnet. Protecting a client’s data from other clients is necessary and can be accomplished using VLAN provisioning, layer 3 filtering and content filtering at the Server Farm entry point. Restricting protocol, source and destination traffic via filters is an option; however additional security practices such as content filtering are required. The Server farm private vlans need to protect the servers located on one subnet from servers located on another subnet.Information Assurance Officer

A firewall rule set can filter network traffic within the printer VLAN to only expected printer protocols. The SA managing the local enclave should identify the printer port traffic within the enclave. Ports commonly used by printers are typically tcp port 515, 631, 1782 and tcp ports 9100, 9101, 9102 but others are used throughout the industry. The SA can review RFC 1700 Port Assignments and review printer vendor documents for the filter rule-set.Information Assurance Officer

Limiting the number of registered MAC addresses on a switch access port can help prevent a CAM table overflow attack. This type of attack lets an attacker exploit the hardware and memory limitations of a switch. If there are enough entries stored in a CAM table before the expiration of other entries, no new entries can be accepted into the CAM table. An attacker will able to flood the switch with mostly invalid MAC addresses until the CAM table’s resources have been depleted. When there are no more resources, the switch has no choice but to flood all ports within the VLAN with all incoming traffic. This happens because the switch cannot find the switch port number for a corresponding MAC address within the CAM table, allowing the switch to become a hub and traffic to be monitored.Information Assurance OfficerDCSP-1

"6-to-4" is a tunneling IPv6 transition mechanism [RFC 3056]. The guidance is the default case, which assumes that 6-to-4 is not being used as an IPv6 transition mechanism. If 6-to-4 is implemented, reference addition 6-to-4 guidance defined in the STIG. Drop all inbound IPv6 packets containing a source address of type 2002::/16. This assumes the 6-to-4 transition mechanism is not being used. Drop all inbound IPv6 packets containing a destination address of type 2002::/16. This assumes the 6-to-4 transition mechanism is not being used.Information Assurance OfficerECSC-1

The decommissioned 6bone allocation (3FFE::/16), RFC 3701 must be blocked. It is no longer a trusted source. Information Assurance Officer

There are a number of outdated tunneling schemes that should be blocked to avoid importing IPv6 packets. DoD IPv6 IA Guidance for MO3 (S0-C7-2) has identified the following to be blocked at the perimeter: Source Demand Routing Protocol (SDRP) AX.25 IP-within-IP Encapsulation Protocol EtherIP protocol Encapsulation Header Protocol PPTPInformation Assurance OfficerECSC-1

Tunnel endpoints that do not have the same controls as the network perimeter requirements become an unprotect entry point into the enclave.Information Assurance OfficerECSC-1

IPv6-in-IPv4 tunnels require explicit configuration (on the tunnel exit point node) of both the tunnel exit point IP address and the corresponding tunnel entry point address . These are the outer IP layer destination and source addresses respectively. Unfortunately, the other three tunnel types (4-in-4, 4-in-6, and 6-in-6) have no such requirement built into the standards. The tunnel exit point address will likely need to be configured for these tunnel types (i.e. nodes are not expected to simply accept tunneling by default) and there MAY be a configuration option to allow the tunnel entry point address to be declared as well. Administrators should attempt to specify both addresses regardless of the IP versions being tunneled if the capability is available for the implementation. There are no requirements in the GRE tunnel standards to check or restrict IP addresses of the tunnel end points (outer IP layer), so it is purely up to the software implementer. The tunnel exit point address will likely need to be configured for these tunnels (i.e. nodes are not expected to simply accept GRE tunneling by default) and there MAY be a configuration option to allow the tunnel entry point address to be declared as well. Administrators should attempt to specify both addresses if the capability is available for the implementation. Information Assurance OfficerECSC-1

Allowing unknown traffic into the enclave creates high risk and potential compromise by an intruder. Protocols used by applications the PPSM has reviewed and determined to require additional mitigation is necessary to protect the GIG.Information Assurance OfficerECSC-1

Having tunnels in a permit any any posture allow traffic to enter and exit the enclave without control from the Information Assurance team or SA.Information Assurance OfficerECSC-1

The Route Processor (RP) is critical to all network operations as it is the component used to build all forwarding paths for the data plane via control plane processes. It is also instrumental with ongoing network management functions that keep the routers and links available for providing network services. Hence, any disruption to the RP or the control and management planes can result in mission critical network outages. In addition to control plane and management plane traffic that is in the router's receive path, the RP must also handle other traffic that must be punted to the RP--that is, the traffic must be fast or process switched. This is the result of packets that must be fragmented, require an ICMP response (TTL expiration, unreachable, etc.) have IP options, etc. A DoS attack targeting the RP can be perpetrated either inadvertently or maliciously involving high rates of punted traffic resulting in excessive RP CPU and memory utilization. To maintain network stability, the router must be able to securely handle specific control plane and management plane traffic that is destined to it, as well as other punted traffic. Using the ingress filter on forwarding interfaces is a method that has been used in the past to filter both forwarding path and receiving path traffic. However, this method does not scale well as the number of interfaces grows and the size of the ingress filters grow. Control plane policing can be used to increase security of routers and multilayer switches by protecting the RP from unnecessary or malicious traffic. Filtering and rate limiting the traffic flow of control plane packets can be implemented to protect routers against reconnaissance and DoS attacks allowing the control plane to maintain packet forwarding and protocol states despite an attack or heavy load on the router or multilayer switch.System AdministratorInformation Assurance OfficerECSC-1

Call home services or features will routinely send data such as configuration and diagnostic information to the vendor for routine or emergency analysis and troubleshooting. The risk that transmission of sensitive data sent to unauthorized persons could result in data loss or downtime due to an attack.Information Assurance OfficerNetwork Security Officer

A scope zone is an instance of a connected region of a given scope. Zones of the same scope cannot overlap while zones of a smaller scope will fit completely within a zone of a larger scope. For example, Admin-local scope is smaller than Site-local scope, so the administratively configured boundary fits within the bounds of a site. According to RFC 4007 IPv6 Scoped Address Architecture (section 5), scope zones are also required to be “convex from a routing perspective”—that is, packets routed within a zone must not pass through any links that are outside of the zone. This requirement forces each zone to be one contiguous island rather than a series of separate islands. As stated in the DoD IPv6 IA Guidance for MO3, “One should be able to identify all interfaces of a zone by drawing a closed loop on their network diagram, engulfing some routers and passing through some routers to include only some of their interfaces.” Hence, it is imperative that the network has documented their multicast topology and thereby knows which interfaces are enabled for multicast. Once, this is done, the zones can be scoped as required.System Administrator

Protocol Independent Multicast (PIM) is a routing protocol used to build multicast distribution tress for forwarding multicast traffic across the network infrastructure. PIM traffic must be limited to only known PIM neighbors by configuring and binding a PIM neighbor filter to those interfaces that have PIM enabled.Information Assurance Officer

A scope zone is an instance of a connected region of a given scope. Zones of the same scope cannot overlap while zones of a smaller scope will fit completely within a zone of a larger scope. For example, Admin-local scope is smaller than Site-local scope, so the administratively configured boundary fits within the bounds of a site. According to RFC 4007 IPv6 Scoped Address Architecture (section 5), scope zones are also required to be “convex from a routing perspective”—that is, packets routed within a zone must not pass through any links that are outside of the zone. This requirement forces each zone to be one contiguous island rather than a series of separate islands. As stated in the DoD IPv6 IA Guidance for MO3, “One should be able to identify all interfaces of a zone by drawing a closed loop on their network diagram, engulfing some routers and passing through some routers to include only some of their interfaces.” Administrative scoped multicast addresses are locally assigned and are to be used exclusively by the enterprise network or enclave. Hence, administrative scoped multicast traffic must not cross the perimeter of the enclave in either direction. Admin-local scope could be used to contain multicast traffic to a portion of an enclave or within a site. This can make it more difficult for a malicious user to access sensitive traffic if the traffic is restricted to links that the user does not have access to. Admin-local scope is encouraged for any multicast traffic within a network that is intended for network management as well as control plane traffic that must reach beyond link-local destinations. Information Assurance Officer

These options are intended to be for the Destination Options header only. The optional and extensible natures of the IPv6 extension headers require higher scrutiny since many implementations do not always drop packets with headers that it can’t recognize and hence could cause a DoS on the target device. In addition, the type, length, value (TLV) formatting provides the ability for headers to be very large. According to the DoD IPv6 IA Guidance for MO3, headers which may be valid but serve no intended use should not be allowed into or out of any network (S0-C2-opt-3).Information Assurance Officer

These options are intended to be for the Hop-by-Hop header only. The optional and extensible natures of the IPv6 extension headers require higher scrutiny since many imiplementtions do not always drop packets with headers that it can’t recognize and hence could cause a DoS on the target device. In addition, the type, lengthe, value (TLV) formatting provides the ability for headers to be very large. According to the DoD IPv6 IA Guidance for MO3, headers which may be valid but serve no intended use should not be allowed into or out of any network (S0-C2-opt-3).Information Assurance OfficerECSC-1

The optional and extensible natures of the IPv6 extension headers require higher scrutiny since many implementations do not always drop packets with headers that it can’t recognize and hence could cause a DoS on the target device. In addition, the type, length, value (TLV) formatting provides the ability for headers to be very large. According to the DoD IPv6 IA Guidance for MO3, headers which may be valid but serve no intended use should not be allowed into or out of any network (S0-C2-opt-3). This option type is associated with the Nimrod Routing system and has no defining RFC document.Information Assurance OfficerECSC-1

The optional and extensible natures of the IPv6 extension headers require higher scrutiny since many implementations do not always drop packets with headers that it can’t recognize and hence could cause a DoS on the target device. In addition, the type, length, value (TLV) formatting provides the ability for headers to be very large. According to the DoD IPv6 IA Guidance for MO3, headers which may be valid but serve no intended use should not be allowed into or out of any network (S0-C2-opt-3). This option type from RFC 1888 (OSI NSAPs and IPv6) has been deprecated by RFC 4048.Information Assurance OfficerECSC-1

The optional and extensible natures of the IPv6 extension headers require higher scrutiny since many implementations do not always drop packets with headers that it can’t recognize and hence could cause a DoS on the target device. In addition, the type, length, value (TLV) formatting provides the ability for headers to be very large. According to the DoD IPv6 IA Guidance for MO3, extension headers with an unknown option type value should not be allowed into or out of any network (S0-C2-opt-3).The optional and extensible natures of the IPv6 extension headers require higher scrutiny since many imiplementtions do not always drop packets with headers that it can’t recognize and hence could cause a DoS on the target device. In addition, the type, lengthe, value (TLV) formatting provides the ability for headers to be very large. According to the DoD IPv6 IA Guidance for MO3, extension headers with an unknow option type value should not be allowed into or out of any network (S0-C2-opt-3).Information Assurance Officer

The 6to4 specific filters accomplish the role of endpoint verification and provide assurance that the tunnels are being used properly. This primary guidance assumes that only the designated 6to4 router is allowed to form tunnel packets. If they are being formed inside an enclave and passed to the 6to4 router, they are suspicious and must be dropped. In accordance with DoD IPv6 IA Guidance for MO3 (S5-C7-8), packets as such must be dropped and logged as a security event.Information Assurance Officer

L2TPv3 sessions can be used to transport layer-2 protocols across an IP backbone. These protocols were intended for link-local scope only and are therefore less defended and not as well-known. As stated in DoD IPv6 IA Guidance for MO3 (S4-C7-1), the L2TP tunnels can also carry IP packets that are very difficult to filter because of the additional encapsulation. Hence, it is imperative that L2TP sessions are authenticated prior to transporting traffic.Information Assurance OfficerECSC-1

As specified in RFC 793, TCP utilizes sequence checking to ensure proper ordering of received packets. RFC 793 also specifies that RST (reset) control flags should be processed immediately, without waiting for out of sequence packets to arrive. RFC 793 also requires that sequence numbers are checked against the window size before accepting data or control flags as valid. A router receiving an RST segment will close the TCP session with the BGP peer that is being spoofed; thereby, purging all routes learned from that BGP neighbor. A RST segment is valid as long as the sequence number is within the window. The TCP reset attack is made possible due to the requirements that Reset flags should be processed immediately and that a TCP endpoint must accept out of order packets that are within the range of a window size. This reduces the number of sequence number guesses the attack must make by a factor equivalent to the active window size. Each sequence number guess made by the attacker can be simply incremented by the receiving connections window size. The BGP peering session can protect itself against such an attack by authenticating each TCP segment. The TCP header options include an MD5 signature in every packet and are checked prior to the acceptance and processing of any TCP packet--including RST flags. One way to create havoc in a network is to advertise bogus routes to a network. A rogue router could send a fictitious routing update to convince a BGP router to send traffic to an incorrect or rogue destination. This diverted traffic could be analyzed to learn confidential information of the site's network, or merely used to disrupt the network's ability to effectively communicate with other networks. An autonomous system can advertise incorrect information by sending BGP updates messages to routers in a neighboring AS. A malicious AS can advertise a prefix originated from another AS and claim that it is the originator (prefix hijacking). Neighboring autonomous systems receiving this announcement will believe that the malicious AS is the prefix owner and route packets to it.ECSC-1