Now that I have IPv6 connectivity to my network, I'm looking for a basic IPv6 firewall configuration for IOS.

It used to be that we could rely on NAT to 'hide' internal (read: outgoing connections only) machines but thankfully we no longer have NAT to do the work for us.

What is a sensible set of IOS configurations / ACLs for a small internal network?


Here's what I've come up with. It works, though I'm not sure if it's optimal. Suggestions welcome!

interface IncomingTunnel0
 ipv6 traffic-filter exterior-in6 in
 ipv6 traffic-filter exterior-out6 out

interface LocalLan0
 ipv6 traffic-filter interior-in6 in
 ipv6 traffic-filter interior-out6 out

ipv6 access-list exterior-in6
 evaluate exterior-reflect sequence 1
 permit ipv6 any host EXTERNAL_ROUTER_ADDRESS sequence 10
 permit tcp any host INTERNAL_ROUTER_ADDRESS eq 22 sequence 11
 permit tcp any host INTERNAL_SERVER_ADDRESS eq 22 sequence 100
 permit icmp any any sequence 800
 deny ipv6 any any sequence 1000

ipv6 access-list exterior-out6
 sequence 10 permit ipv6 MY_ASSIGNED_SUBNET::/48 any reflect exterior-reflect

ipv6 access-list interior-in6
 permit ipv6 fe80::/10 any
 permit ipv6 INTERNAL_LAN_SUBNET::/64 any

ipv6 access-list interior-out6
 permit ipv6 any any

For those of you not familiar with reflexive access-lists, it's how you do stateful connection tracking. In other words, it's what allows responses to those outgoing connections to come back to you.


I'd really recommend using inspection instead of reflexive access lists - e.g:

ipv6 inspect name IPV6FIREWALLINSPECT tcp
ipv6 inspect name IPV6FIREWALLINSPECT udp
ipv6 inspect name IPV6FIREWALLINSPECT icmp

int IncomingTunnel0
 ipv6 inspect IPV6FIREWALLINSPECT out
 ipv6 traffic-filter IPV6FIREWALL in

ipv6 access-list IPV6FIREWALL
 sequence 10 permit (explicit inbound traffic)
 sequence 20 deny ipv6 any any

Much cleaner config. sho ipv6 inspect session will show you all the outbound sessions for which return traffic is permitted.

  • Note: you need to add "sequence 5 permit icmp any any" to the IPV6FIREWALL access-list definition, or else you won't be able to use the IPv6 connection at all; ICMP is necessary for v6 in a way that you could get away with ignoring in v4. – Cerebrate Aug 18 '16 at 16:35
  • Also, if your tunnel or ISP provides addresses, prefixes, or other configuration data using DHCPv6, you will also need to add "sequence 10 permit udp any any eq 546", or the interface won't configure correctly. – Cerebrate Aug 18 '16 at 16:38
  • As an additional note, I have learned that there is a bug in IOS 12 that causes inspection of IPv6 traffic to cause downloads or other large TCP transfers to stall. I've had to discontinue using inspection because of this. – Cerebrate Aug 20 '16 at 20:40

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