V-230160

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.

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This requirement is not applicable for the DODIN Backbone. 

Review the router configuration and determine if filters are bound to the applicable interfaces to drop all inbound IPv6 packets containing an undefined option type value regardless of whether they appear in a Hop-by-Hop or Destination Option header. Undefined values are 0x02, 0x03, 0x06, 0x9 – 0xE, 0x10 – 0x22, 0x24, 0x25, 0x27 – 0x2F, and 0x31 – 0xFF.

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

interface interface gigabitethernet 0/2/0/2
 ipv6 address 2001::1:0:22/64
 ipv6 access-group FILTER_IPV6 ingress

Step 2: Verify that the ACL drops IPv6 packets containing Hop-by-Hop or Destination Option extension headers as shown in the example below.

ipv6 access-list FILTER_IPV6
 10 deny 60 any any dest-option log
 20 deny hbh any any dest-option log
 30 permit  …
 …
 …
 …
 90 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 router is not configured to drop IPv6 packets containing a Hop-by-Hop or Destination Option extension headers with destination options, this is a finding.