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

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-237776	CISC-RT-000397	SV-237776r856673_rule	CCI-002403	medium
Description
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.
STIG			Date
Cisco IOS XE Switch RTR Security Technical Implementation Guide			2025-05-20

Details

Check Text (C-237776r856673_chk)

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 the NSAP address option within Destination Option header as shown in the example below. ipv6 access-list FILTER_IPV6 deny 60 any any dest-option-type 195 log permit ipv6 … … … … deny ipv6 any any log If the switch is not configured to drop IPv6 packets containing the NSAP address option within Destination Option header, this is a finding.

Fix Text (F-40946r856269_fix)

Configure the switch to to drop IPv6 packets containing the NSAP address option within 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-type 195 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