IPv6 Prefix announcing

Greetings NANOG,
I've always been under the impression its best practice to only announce
prefixes of a /24 and above when it comes to IPv4 and BGP.
I was wondering if something similar had been agreed upon regarding IPv6.
And if That's the case, What's the magic number? /32? /48? /64?

Nick Olsen
Network Operations (855) FLSPEED x106

You're likely to get different answers to this, but the 'magic number' appears to be /48. Looking in the v6 BGP table, you will likely find smaller prefixes than that, but a number of the major carriers seem to be settling on /48 as the smallest prefix they will accept. /48 is also the smallest block most of the RIRs will assign to end-users.


Funny enough, some carriers actually require the 'smallest' as being /32... :frowning:

Vote with your wallet.

Some carriers would prefer if only transit free networks were allowed to originate routes. Doesn't mean you should follow their lead.

From: Kate Gerry
Sent: Tuesday, April 26, 2011 9:39 AM
To: 'Justin M. Streiner'; nanog@nanog.org
Subject: RE: IPv6 Prefix announcing

Funny enough, some carriers actually require the 'smallest' as being
/32... :frowning:

That might be true in PA space, but PI space is issued down to /48. I
am not aware of anyone who filters smaller than a /32 in PI space though
that doesn't mean it doesn't happen. The largest holdout was Verizon
but my understanding is they now accept a /48 in PI space.


A /32 is the smallest prefix issued in PA and some networks will not
accept a prefix smaller than /32 from PA address space.
A /48 is the smallest prefix issued in PI and some networks will not
accept a prefix smaller than /48 from PI address space.

In other words, if you are going to attempt to multihome a /48
allocation from your provider's aggregate, you are better off getting
your own provider independent block.

Hi Nick,

At this point, you can depend on being able to announce a /32 from any
block and a /48 from an RIR block designated for end-user assignments.
Many carriers have more permissive policies but all of any consequence
now allow at least that.

Bill Herrin

I know that used to be true, but, to the best of my knowledge, everyone is now accepting
down to /48s in provider independent ranges. Some still require /32 or shorter in the provider aggregate ranges.


This is becoming the exception now, not the rule.

Last year I was fighting with Verizon about their refusal to carry /48s.
That, together with the impasse of figuring out how to put dual stack
IPv6 on an Ethernet port (it was delivered as IPv4 only multiple times),
I never accepted it and went with a competitor who got it right the
first time. However, I've had several sources tell me Verizon has since
backpedaled and now accepts /48s.


*> 2001:67C:120::/48 2001:504:16::1B1B 150 0 6939 701 12702 43751 6716 i