V-237776

Discussion

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.

Check Content

This requirement is not applicable for the DODIN Backbone. 

Review the switch configuration and determine if filters are bound to the applicable interfaces to drop IPv6 packets containing a Destination Option header with option type value of 0xC3 (NSAP address). 

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