From Perimeter Router Security Technical Implementation Guide
Part of Outbound ICMPv6 traffic is not blocked
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.
Review the configuration and ensure only approved ICMP types are permitted to exit the enclave. Use source and destination filtering where appropriate. For the purpose of troubleshooting WAN link connectivity, inbound ICMP echo requests destined to the premise router’s external IP address and outbound echo replies originated by the premise router are permitted if the following conditions are met: 1. Inbound ICMP echo requests are restricted to packets sourced from a specific IP address and destined to the premise router’s external interface address. This filtering must be done via input ACL assigned to the premise router’s external interface. 2. Inbound ICMP echo requests must be rate limited via input service policy assigned to the premise router’s external interface or the control plane (see NET0966). Note: Outbound traffic generated by the router can only be filtered by using an outbound service policy on the control plane for IOS routers or outbound firewall on the routing engine for JUNOS routers. However, the router will only generate ICMP echo replies for ICMP echo requests that it is allowed to receive; hence, there is no need to filter these.
The network element must be configured to include controls to block outbound ICMP traffic message types.
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