Category: IPv6

If you want to display any IPV6-related BGP objects (neighbors, routes …) you can use the familiar BGP commands, but have to prefix them with show ip bgp ipv6 unicast. For example, to display the BGP neighbors active in the IPv6 address family, you would use show ip bgp ipv6 unicast summary command. I doubt you like so much typing (I don't, just entering the IPv6 addresses is enough for me); luckily Cisco IOS has aliases - just configure alias exec bgpv6 show ip bgp ipv6 unicast and (for consistency) alias exec bgpv4 show ip bgp ipv4 unicast.

Update 2010-03-12: Cisco IOS also supports show bgp ipv6 unicast command, which (at least) makes BGP ipv4-agnostic.

If you want to understand the buzz raised recently about IP version 6, and your daily job includes more budget meetings, payroll discussions or strategy/operational planning than router configuration, Global IPv6 Strategies: From Business Analysis to Operational Planning (Cisco Press, 2008) is a mandatory book for you. The authors, Patrick Grossetete, Ciprian P. Popoviciu and Fred Wettling, are weathered veterans of the IPv6 battles, and their lengthy experience with IPv6 shines through the pages of this book.

The brief display of the state of IPv6 interfaces in the router (show ipv6 interface brief) is significantly different from the well-known show ip interface brief display as the IPv6 address might not fit in the same line as all the other data. To filter the printout and display only the operational interfaces, you have to replace the include filter with the section filter, which displays all the lines matching the regular expression as well as associated follow-up lines.

PE-A#show ipv6 interface brief | section up
Serial1/0                  [up/up]
    unassigned
Serial1/1                  [up/up]
    FE80::C800:CFF:FEA7:0
Loopback0                  [up/up]
    unassigned

The definition of the associated follow-up lines depends on the printout. Usually the indented lines are assumed to belong to a section, but you might be surprised.

One of the obscure facts about IPv6 OSPF (OSPFv3) is that it uses a 32-bit router ID like OSPFv2. It’s a reasonable choice; I have yet to see an OSPF network with over a billion routers. However, could you guess how this requirement is implemented in Cisco IOS? OSPFv3 searches for an IPv4 address (effectively the same algorithm used by OSPFv2) to get the router ID for the IPv6 routing process. Neat, isn’t it?

You might wonder what happens if you want to configure an IPv6-only router. OSPF won’t start unless you configure the router ID manually. And, no, you cannot enter a number (which would be the expected format, as the router ID is just a number in the IPv6 world); you have to enter an IPv4 address. Long live IPv4 :))

In response to my Never-Ending Story of IP Fragmentation, Stojanco Cavdarov made an interesting observation: routers are not allowed to fragment IPv6 packets, they have to respond back with ICMP unreachable (effectively, routers behave as if IPv6 packets would have an implicit don't fragment bit).

To make life easier for non-TCP IPv6 applications (TCP is supposed to use Path MTU Discovery), the minimum IPv6 packet size that has to be supported on all links was increased to 1280 bytes (which, incidentally, fits very nicely into GRE+IPSec envelope transported across links with 1500-byte MTU).

A while ago I was asked to write an article about IPv6 training. I could just cover the training aspect, like what’s offered (answer: not much) and whether someone can train the whole operations team like you could in the IPv4 or MPLS/VPN world (answer: no), but I wanted to understand whether anyone is really using IPv6 in a production network.

I found a few academic networks (after all, there are about 2000 IPv6 prefixes assigned and someone should be doing something with them), but not much of what I would call a real production environment, which is a bad thing, as it looks like the IPv4 address space will get saturated in a few years.