[167547] in North American Network Operators' Group
Re: IPv6 /48 advertisements
daemon@ATHENA.MIT.EDU (Owen DeLong)
Wed Dec 18 14:07:53 2013
From: Owen DeLong <owen@delong.com>
In-Reply-To: <1A5C3257AD8D4946A4B497A6FAF501743C45E5B476@EXCH07-01.apollogrp.edu>
Date: Wed, 18 Dec 2013 11:06:58 -0800
To: Cliff Bowles <cliff.bowles@apollogrp.edu>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Dec 18, 2013, at 08:11 , Cliff Bowles <cliff.bowles@apollogrp.edu> =
wrote:
> I accidentally sent this to nanog-request yesterday. I could use some =
feedback from anyone that can help, please.
>=20
> Question: will carriers accept IPv6 advertisements smaller than /48?
Generally, no. Since a /48 should represent nothing larger than a single =
site, it's not very reasonable to want to route something longer in =
general.
> Our org was approved a /36 based on number of locations. The bulk of =
those IPs will be in the data centers. As we were chopping up the =
address space, it was determined that the remote campus locations would =
be fine with a /60 per site. (16 networks of /64). There are usually =
less than 50 people at the majority of these locations and only about 10 =
different functional VLANs (Voice, Data, Local Services, Wireless, Guest =
Wireless, etc...).
That's still poor planning, IMHO. You can easily get more than enough =
/48s to give one to each location. There's absolutely no advantage in =
the IPv6 world to being stingy with address space and no benefit to not =
putting at least a /48 at every location.
You've got 10 VLANs, so you're wasting at most 65,526 networks. Compare =
that to the fact that using a /64 for a VLAN with less than 2,000,000 =
hosts on it will wast at least 18,446,744,073,707,551,616 addresses and =
you begin to realize that sparse addressing in IPv6 and large amounts of =
excess address capacity are intentional.
> Now, there has been talk about putting an internet link in every =
campus rather than back hauling it all to the data centers via MPLS. =
However, if we do this, then would we need a /48 per campus? That is =
massively wasteful, at 65,536 networks per location. Is the /48 =
requirement set in stone? Will any carriers consider longer prefixes?
Massively wasteful is a fact of life in IPv6. Consider it this way... =
There are two ways to waste address space. One way is, as you describe =
above, deploying it to locations that are unlikely to fully utilize it.
Another way is to leave it sitting in a free pool until long after the =
protocol is no longer useful.
With IPv6, we're not so much choosing between wasting address space or =
not. We're choosing how much address space gets wasted using method 1 =
vs. how much gets wasted using method 2. Ideally, we arrive at the =
protocol end of life with some space remaining in both categories of =
waste.
> I know some people are always saying that the old mentality of =
conserving space needs to go away, but I was bitten by that IPv4 issue =
back in the day and have done a few VLSM network overhauls. I'd rather =
not massively allocate unless it's a requirement.
It's a requirement and not massively allocating will bite you harder in =
IPv6 than space did in IPv4.
IPv4 was designed for a different kind of network. It was designed to =
support some labs and some institutional environments. It was never =
intended to be the global public internet. IPv6 has been designed with =
the idea of addressing absolutely everything from the ground up. The =
design allows for plenty of /48s to number every building that could =
possibly fit on every planet in the solar system and several other solar =
systems.
Frankly, a /48 per campus is underallocating for any campus that has =
more than one building.
Owen
