IPv6 Access-list on Cisco IOS

As explained in my first lesson that introduces access-lists, we can use access-lists for filtering (blocking packets) or selecting traffic (for VPNs, NAT, etc).

This also applies to IPv6 access-lists which are very similar to IPv4 access-lists. There are two important differences however:

  • IPv4 access-lists can be standard or extended, numbered or named. IPv6 only has named extended access-lists.
  • IPv4 access-lists have an invisible implicit deny any at the bottom of every access-list. IPv6 access-lists have three invisible statements at the bottom:
    • permit icmp any any nd-na
    • permit icmp any any nd-ns
    • deny ipv6 any any

The two permit statements are required for neighbor discovery which is an important protocol in IPv6, it’s the replacement for ARP.

When you use a deny ipv6 any any at the bottom of your access-list, make sure you also add the two permit statements for neighbor discovery just before the final statement or this traffic will be dropped.

Having said that, let’s take a look at the configuration.

Configuration

For this demonstration we only need two routers:

R1 R2 2001 DB8 0 12

I’ll use subnet 2001:DB8:0:12::/64 in between R1 and R2. To demonstrate the access-list, I’ll create one inbound on R2 and we will try to filter some packets from R1. Let’s take a look at the access-list:

R2(config)#ipv6 access-list ?
  WORD        User selected string identifying this access list
  log-update  Control access list log updates

As you can see above the only option is the named access-list. There’s also no option for standard or extended access-list. Let’s create that access-list:

R2(config)#ipv6 access-list R1_TRAFFIC

I’ll call it “R1_TRAFFIC”. Here are our options when we create a statement:

R2(config-ipv6-acl)#permit ?
  <0-255>             An IPv6 protocol number
  X:X:X:X::X/<0-128>  IPv6 source prefix x:x::y/<z>
  ahp                 Authentication Header Protocol
  any                 Any source prefix
  esp                 Encapsulation Security Payload
  host                A single source host
  icmp                Internet Control Message Protocol
  ipv6                Any IPv6
  pcp                 Payload Compression Protocol
  sctp                Streams Control Transmission Protocol
  tcp                 Transmission Control Protocol
  udp                 User Datagram Protocol

This is similar to IPv4 access-lists. You can pick any protocol you like. Let’s see if we can permit telnet traffic from R1 and deny everything else:

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Forum Replies

  1. I think you are missing a keyword in this line:

    <strong>permit host 2001:db8:0:12::1 any eq 23
    
    Think it should be:
    permit tcp host 2001:db8:0:12::1 any eq 23</strong>
    

  2. Hi Jeppe,

    For sure, not sure what went wrong there. Just fixed it…

    Also added my configs at the bottom of the lesson.

    Rene

  3. Hi Rene

    Will the 3 implicit permit/deny statements won’t show up when we use the show access-list statements?

    Thanks
    Palani

  4. Palani,
    That’s right–the 3 statements will not appear with a show access-list command.

  5. Hi Rene,

    I think telnet traffic filter in line vty NOT per interface ? correct me if I wrong.

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