IPv6 Access-list on Cisco IOS

As explained in my first tutorial 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. On your Introduction to Access-Lists on Cisco IOS Router lesson, you have, in the picture for where to place the ACL, the word inbound twice. I believe that the top router should be “inbound” and the bottom router should be the “outbound.”

  2. Hi Eric,

    Thanks for pointing that out, I just fixed it.

    Rene

  3. Is there any example on how to configure classification on a router.

  4. Asi
    The first thing you have to decide is whether you are creating an standard or extended access-list. The next decision to make is whether you wanted to use an access-list number or an access-list name. In the examples you gave, you chose to use named access-lists for both (out_acsz_in). Also, in your example, we must be using extended access-lists (because you specified the destination of the traffic you are permitting).

    Let’s look at your two examples, and reconfigure them so they are using the proper syntax.
    Your first example is this:
    (config)#access-l

    ... Continue reading in our forum

  5. Hello Siu Kai L,

    Both inbound and outbound get the job done, they filter packets. It depends on the scenario which one you might want to use. For example, let’s say you have a router with 4 interfaces:

    * 1x WAN interface that connects to the Internet
    * 3x LAN interface

    Let’s say you want to restrict internet traffic from your LAN to the Internet. You could attach the same access-list INBOUND on all three LAN interfaces, or you can attach the access-list OUTBOUND on your WAN interface. Both get the job done, the only difference is you have to apply it once inste

    ... Continue reading in our forum

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