I have a new 881 router loaded with the latest 15.1.3T software, and I'm trying to get it connected to the Comcast 6RD IPv6 routers. (I'm on a Comcast cable modem.)
I've been trying to follow the directions from these links:
I am getting a delegated prefix from Comcast, so I know I'm connecting to their BR routers.
RouterA-new#sho tun 6rd pref 18.104.22.168 tu6
6RD Prefix: 2001:55C:45FC:5042::
But, that doesn't seem to be properly following the general-prefix on the tunnel (it's missing the ::45FC:5042::):
RouterA-new#sho ipv int brie tun 6
I think the problem is just some stupid wrong/missing config in my tunnel setup. Or an ipv6 noob issue. This is the current state of what I have so far, cobbled from the links above, and with several shotgun troubleshooting tweaks:
ipv6 general-prefix Comcast6RD 6rd Tunnel6
description Comcast 6RD IPv6 tunnel.
no ip address
no ip redirects
ipv6 address Comcast6RD ::/64 eui-64
tunnel source Vlan1
tunnel mode ipv6ip 6rd
tunnel 6rd prefix 2001:55C::/32
tunnel 6rd br 22.214.171.124
ip address 10.20.222.1 255.255.255.0
ip nat inside
ip virtual-reassembly in
zone-member security in-zone
ip tcp adjust-mss 1452
I've tried putting the ipv6 address on the Vlan1 interface, as in the docwiki link, but then I get the overlapping address error listed in the link. But, when I try just putting the 'ipv6 enable' command on the tunnel, then I don't get any 2001:55C:: addresses assigned.
Feb 28 04:16:38.622: %IPV6_ADDRESS-3-ADDRESS_CFG: 2001:55C:A14:DE01::/64 can not be configured on Vlan1, 2001:55C:A14:DE01::/64 is overlapping with 2001:55C:A14:DE01::/128 on Tunnel6
So, does anyone have a working 6RD config for Comcast? Or can you point out what I'm doing wrong?
I think the problem is with your default v6 route - "ipv6 route ::/0 Tunnel6". You are basically telling the CE that everything is directly connected to the 6rd network, so it assumes whatever comes after the 6rd prefix is the embedded ipv4 address for the destination. Could you try to remove this line, and replace it with "ipv6 route ::/0 Tunnel6 2001:55C:45FC:5042::"? This should tell the CE to send everything else to the BR instead. Give it a try and see if that helps any.
You are correct that by not configuring "tunnel 6rd ipv4 prefix-len", it defaults to a prefix length of 0, which means the CE ipv4 addresses cannot be aggregated and therefore all 32 bits will be used. So with a 6rd prefix of 32 bits and 32 bits of ipv4, your delegated prefix is 64 bits (longest allowed by the 6rd spec), which implies you won't be able to subnet within that delegated prefix.
Hope this helps.