The Cisco perimeter router must be configured to drop IPv6 packets containing the NSAP address option within Destination Option header.

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 cannot recognize, and hence could cause a Denial-of-Service on the target device. In addition, the type, length, value (TLV) formatting provides the ability for headers to be very large. This option type from RFC 1888 (OSI NSAPs and IPv6) has been deprecated by RFC 4048.

This requirement is not applicable for the DODIN Backbone.

Review the router configuration to determine if it is compliant with this requirement.

Step 1: Verify that an inbound IPv6 ACL has been configured on the external interface.

interface gigabitethernet1/0 ipv6 address 2001::1:0:22/64 ipv6 traffic-filter FILTER_IPV6 in

Step 2: Verify that the ACL drops IPv6 packets containing a Destination Option header as shown in the example below.

ipv6 access-list FILTER_IPV6 deny 60 any any dest-option log permit ipv6 … … … … deny ipv6 any any log

Note: Cisco has deprecated the dest-option-type command used to filter by option type within the Destination Option header. Therefore, all packets with the Destination Option header must be dropped.

If the router is not configured to drop IPv6 packets containing a Destination Option header, this is a finding.

Configure the router to drop IPv6 packets containing a Destination Option header as shown in the example below.

R1(config)#ipv6 access-list FILTER_IPV6 R1(config-ipv6-acl)#deny 60 any any dest-option log R1(config-ipv6-acl)#permit … … … … R1(config-ipv6-acl)#deny ipv6 any any log R1(config-ipv6-acl)#exit R1(config)#int g1/0 R1(config-if)#ipv6 traffic-filter FILTER_IPV6 R1(config-if)#end