The Cisco ISR 4000 Series router must configure the maximum hop limit value to at least 32.

From Cisco IOS XE Release 3 RTR Security Technical Implementation Guide

Associated with: CCI-001097

SV-88811r1_rule The Cisco ISR 4000 Series router must configure the maximum hop limit value to at least 32.

Vulnerability discussion

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.

Check content

Review the Cisco ISR 4000 Series router configuration to determine if the maximum hop limit for IPv6 Neighbor Discovery has been configured. The configuration would look similar to the example below: ipv6 hop-limit 32 If the router does not have the maximum hop limit value set to at least "32", this is a finding. If it has been configured, then it must be set to at least "32". If it has not been configured, it must be determined what the default value is. If the default value is below "32" and the maximum hop limit value has not been configured (set to at least "32"), this is a finding. In any case, maximum hop limit must be at least "32".

Fix text

Configure the Cisco ISR 4000 Series router IPv6 Neighbor Discovery maximum hop limit value to at least "32". The configuration would look similar to the example below: ipv6 hop-limit 32

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