Router Security Requirements Guide

Information flow control regulates authorized information to travel within a network and between interconnected networks. Controlling the flow of network traffic is critical so it does not introduce any unacceptable risk to the network infrastructure or data. An example of a flow control restriction is blocking outside traffic claiming to be from within the organization. For most routers, internal information flow control is a product of system design.

A scope zone is an instance for 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.

Protocol Independent Multicast (PIM) is a routing protocol used to build multicast distribution trees 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.

If multicast traffic is forwarded beyond the intended boundary, it is possible that it can be intercepted by unauthorized or unintended personnel. Administrative scoped multicast addresses are locally assigned and are to be used exclusively by the enterprise network or enclave. Administrative scoped multicast traffic must not cross the enclave perimeter in either direction. Restricting multicast traffic makes it more difficult for a malicious user to access sensitive traffic. Admin-Local scope is encouraged for any multicast traffic within a network intended for network management, as well as for control plane traffic that must reach beyond link-local destinations.

An inactive interface is rarely monitored or controlled and may expose a network to an undetected attack on that interface. Unauthorized personnel with access to the communication facility could gain access to a router by connecting to a configured interface that is not in use.

Without a filter configured to deny all traffic on inactive interfaces, a router interface connected to an external network will expose the router and backbone network to malicious traffic.

Enclaves with Alternate Gateway connections must take additional steps to ensure there is no compromise on the enclave network or NIPRNet. Without verifying the destination address of traffic coming from the site's Alternate Gateway, the perimeter router could be routing transit data from the Internet into the NIPRNet. This could also make the perimeter router vulnerable to a DoS attack as well as provide a backdoor into the NIPRNet. The DoD enclave must ensure the ingress filter applied to external interfaces on a perimeter router connecting to an Approved Gateway is secure through filters permitting packets with a destination address belonging to the DoD enclave's address block.

The perimeter router will not use a routing protocol to advertise NIPRNet addresses to Alternate Gateways. Most ISPs use Border Gateway Protocol (BGP) to share route information with other autonomous systems, that is, any network under a different administrative control and policy than a local site. If BGP is configured on the perimeter router, no BGP neighbors will be defined to peer routers from an AS belonging to any Alternate Gateway. The only allowable method is a static route to reach the Alternate Gateway.

If the static routes to the Alternate Gateway are being redistributed into an EGP or IGP to a NIPRNet gateway, this could make traffic on other NIPRNet flow to that particular router and not to the IAP routers. This could not only wreak havoc with traffic flows on NIPRNet, but it could overwhelm the connection from the router to the NIPRNet gateway(s) and also cause traffic destined for outside of NIPRNet to bypass the defenses of the Internet Access Points.

If the gateway router is not a dedicated device for the OOBM network, implementation of several safeguards for containment of management and production traffic boundaries must occur. Since the managed and management network are separate routing domains, configuration of separate IGP routing instances is critical on the router to segregate traffic from each network.

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.

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 directly connect 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, both data plane and control plane, does not leak into the managed network and that production traffic does not leak into the management network.

Information flow control regulates where information is allowed to travel within a network and between interconnected networks. The flow of all network traffic must be monitored and controlled so it does not introduce any unacceptable risk to the network infrastructure or data. Restrictions can be enforced based on source and destination IP addresses as well as the ports and services being requested. This requirement should enforce the deny-by-default policy whereby only the known and accepted traffic will be allowed outbound and inbound.

A rogue router could send a fictitious routing update to convince a site's perimeter router to send traffic to an incorrect or even a rogue destination. This diverted traffic could be analyzed to learn confidential information about the site's network, or merely used to disrupt the network's ability to communicate with other networks. This is known as a "traffic attraction attack" and is prevented by configuring neighbor router authentication for routing updates. This requirement applies to all IPv4 and IPv6 protocols that are used to exchange routing or packet forwarding information; this includes all Interior Gateway Protocols (such as OSPF, EIGRP, and IS-IS) and Exterior Gateway Protocols (such as BGP), MPLS-related protocols (such as LDP), and Multicast-related protocols.

If the keys used for routing protocol authentication are guessed, the malicious user could create havoc within the network by advertising incorrect routes and redirecting traffic. Changing the keys frequently reduces the risk of them eventually being guessed.

A compromised router introduces risk to the entire network infrastructure as well as data resources that are accessible via the network. The perimeter defense has no oversight or control of attacks by malicious users within the network. Preventing network breaches from within is dependent on implementing a comprehensive defense-in-depth strategy including securing each device connected to the network. This is accomplished by following and implementing all security guidance applicable for each node type. A fundamental step in securing each router is to enable the capabilities required for operation.

Routers not protected with strong passwords provide the opportunity for anyone to crack the password, thus gaining access to the system and the network. All passwords must be kept and known only by the account user who created the password. Malicious users can gain knowledge of passwords during the authentication process by sniffing local traffic between the router and the authentication server. It is imperative the authentication process implements cryptographic modules adhering to the standards approved by the federal government.

Routers not protected with strong passwords provide the opportunity for anyone to crack the password, thus gaining access to the system and the network. All passwords must be kept and known only by the account user who created the password. Malicious users can gain knowledge of passwords during the authentication process by sniffing local traffic between the router and the authentication server. It is imperative the authentication process implements cryptographic modules adhering to the standards approved by the federal government.

As described in RFC 3682, the GTSM is designed to protect a router's IP-based control plane from DoS attacks. Many attacks focused on CPU load and line-card overload can be prevented by implementing GTSM on all eBGP-speaking routers. GTSM is based on the fact that the vast majority of control plane peering is established between adjacent routers; that is, the eBGP peers are either between connecting interfaces or between loopback interfaces. Since TTL spoofing is considered nearly impossible, a mechanism based on an expected TTL value provides a simple and reasonably robust defense from infrastructure attacks based on forged control plane traffic.

A compromised host in an enclave can be used by a malicious actor as a platform to launch cyber attacks on third parties. This is a common practice in “botnets”, which are a collection of compromised computers using malware to attack (usually DDoS) other computers or networks. DDoS attacks frequently leverage IP source address spoofing, in which packets with false source IP addresses send traffic to multiple hosts, which then send return traffic to the hosts with the IP addresses that were forged. This can generate significant, even massive, amounts of traffic. Therefore, protection measures to counteract IP source address spoofing must be taken. The router must not accept any outbound IP packets that contain an illegitimate address in the source address field by enabling Unicast Reverse Path Forwarding (uRPF) strict mode or by implementing an egress ACL. Unicast Reverse Path Forwarding (uRPF) provides an IP address spoof protection capability. When uRPF is enabled in strict mode, the packet must be received on the interface that the device would use to forward the return packet.

Denial of service is a condition when a resource is not available for legitimate users. Packet flooding DDoS attacks are referred to as volumetric attacks and have the objective of overloading a network or circuit to deny or seriously degrade performance, which denies access to the services that normally traverse the network or circuit. Volumetric attacks have become relatively easy to launch using readily available tools such as Low Orbit Ion Cannon or by botnets. Measures to mitigate the effects of a successful volumetric attack must be taken to ensure that sufficient capacity is available for mission-critical traffic. Managing capacity may include, for example, establishing selected network usage priorities or quotas and enforcing them using rate limiting, Quality of Service (QoS), or other resource reservation control methods. These measures may also mitigate the effects of sudden decreases in network capacity that are the result of accidental or intentional physical damage to telecommunications facilities (such as cable cuts or weather-related outages).

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.

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 a DoS on the network that allocated the block of addresses and may cause a 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 redistribute IGP routes into BGP, thereby leaking internal routes.

The Neighbor Discovery protocol allows a hop limit value to be advertised by routers in a Router Advertisement message to be used by hosts instead of the standardized default value. If a very small value was configured and advertised to hosts on the LAN segment, communications would fail due to the hop limit reaching zero before the packets sent by a host reached their destination.

The Route Processor (RP) is critical to all network operations because 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. 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 handled in the routers receive path, the RP must also punt other traffic to the RP, since the traffic must be fast or process switched. This includes fragmented packets requiring an ICMP response (e.g., TTL expiration, unreachable) including IP options. A DoS attack targeting the RP can perpetrate through either inadvertent or malicious traffic involving high rates of punted traffic resulting in excessive RP CPU and memory utilization. To maintain network stability and RP security, the router must be able to handle specific control plane and management plane traffic that is destined to the RP, as well as other punted traffic. In the past, one method of filtering was to use ingress filters on forwarding interfaces 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 increases the 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.

Unrestricted traffic may contain malicious traffic that poses a threat to an enclave or to other connected networks. Additionally, unrestricted traffic may transit a network, which uses bandwidth and other resources. Traffic can be restricted directly by an ACL (which is a firewall function) or by Policy Routing. Policy Routing is a technique used to make routing decisions based on a number of different criteria other than just the destination network, including source or destination network, source or destination address, source or destination port, protocol, packet size, and packet classification. This overrides the router's normal routing procedures used to control the specific paths of network traffic. It is normally used for traffic engineering, but can also be used to meet security requirements; for example, traffic that is not allowed can be routed to the Null0 or discard interface. Policy Routing can also be used to control which prefixes appear in the routing table. Traffic can be restricted directly by an ACL (which is a firewall function), or by Policy Routing. This requirement is intended to allow network administrators the flexibility to use whatever technique is most effective.