The Cisco perimeter switch must be configured to drop IPv6 packets containing a Hop-by-Hop or Destination Option extension header with an undefined option type.

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 requirement is not applicable for the DOWIN Backbone.

Review the switch 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 deny hbh 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 and Hop-by-Hop header. Therefore, all packets with the Destination Option header and Hop-by-Hop options must be dropped.

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

Configure the switch to drop all inbound IPv6 packets containing destination option type values regardless of whether they appear in a Hop-by-Hop or Destination Option header as shown in the example below.

SW1(config)#ipv6 access-list FILTER_IPV6 SW1(config-ipv6-acl)#deny 60 any any dest-option log SW1(config-ipv6-acl)#deny hbh any any dest-option log SW1(config-ipv6-acl)#permit … … … … SW1(config-ipv6-acl)#deny ipv6 any any log SW1(config-ipv6-acl)#exit SW1(config)#int g1/0 SW1(config-if)#ipv6 traffic-filter FILTER_IPV6 SW1(config-if)#end