Using /126 for IPv6 router links

Glen Turner gdt at
Mon Jan 25 00:42:04 UTC 2010

On 24/01/10 12:54, Owen DeLong wrote:
> Use the /64... It's OK... IPv6 was designed with that in mind.

I'd suggest using a /126. For two reasons.

1) Using EUI-64 addresses on router-router links is an error, the
    consequences of which you encounter the first time you replace
    some faulty hardware.[1]  I have made this error :-(  If you
    are not using EUI-64 then assigning a non-autoconf /64 is no
    less or more work than assigning a non-autoconf /126.

2) Having a block of addresses for router-router links (and other blocks
    for other infrastructure such as loopbacks and unicast) makes ACLs
    much simpler. Using a /126 means that this block can last for a long,
    long time, reducing configuration maintenance.

Cheers, Glen

[1] Basically, interface addresses end up scattered through the
     router's configuration (some manufacturers are better than
     others in this regard). Tracking down all the references to
     an address and changing the config merely as the result of a
     hardware swap is painful and adds complexity at a time when
     it is not desired.

  Glen Turner  <>
  Network Engineer
  Australia's Academic & Research Network  <>

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