IPv6 /48 advertisements

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1

I accidentally sent this to nanog-request yesterday. I could use some feedback from anyone that can help, please.

Question: will carriers accept IPv6 advertisements smaller than /48?

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...).

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?

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.

Thanks in advance.

CWB

2

Most of the carriers I've seen won't accept anything smaller than /48. You have 4096 /48s to use in your /36. The bigger concern for carriers/ISPs
is IPv6 routing table bloat from carrying lots of small individual
advertisements.

jms

3

Question: will carriers accept IPv6 advertisements smaller than /48?

Not generally, no.

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...).

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?

/48 per site is the standard.

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.

You need to throw out all old thinking in terms of what happened in
IPv4. Current ARIN policy allows a /48 per site and that is how you
should architect the network.

4

If you’re talking about announcing each location separately, then RIPE have a couple of useful articles about prefix visibility on Ripe Labs:

https://labs.ripe.net/Members/emileaben/ripe-atlas-a-case-study-of-ipv6-48-filtering
https://labs.ripe.net/Members/dbayer/visibility-of-prefix-lengths

Otherwise I guess you’ll need to talk to your chosen carrier(s) about aggregating your space for you, which will come down to their policies on what routes they will carry internally.

Edward Dore
Freethought Internet

5

Regardless of the carriers, you'll find most ASs on the internet only
listen to /48 or larger. So even if you get your prefixes accepted by your
provider, don't assume you can get anywhere, or have your packets not fall
in to uRPF blackholes randomly without a larger aggregate announcement.

-Blake

6

It's standard to filter out anything longer than /48.

Your /36 prefix was chosen based on the number of sites, with a /48 per site, so just keep it simple. Trying to manage it in the way IPv4 addresses were managed will just ensure that you will have the same headaches of micro managing sub allocations and trying to guess the right sizes. The address space in V6 is large enough that you don't have to spend your time worrying about this, and that's one of the reasons for using a /48 at each site.

Think of an IPv6 /48 like you would think of an IPv4 /24 - except that it's the right size for either your house or your university campus.

Laszlo

7

I had a feeling... thanks for the feedback.

CWB

8

In GRH (http://www.sixxs.net/tools/grh/) I only see 2620:0:5030::/48,
thus did you get another/new/updated one very recently?

Note that there are quite a few ISPs who filter on the assigned prefix
length, especially for PA address space which should be Aggregated by
the Provider (PA).

Likely your space comes out of one of the PI blocks, in which case rules
tend to be a bit more lax, hence a /48 should get through.

Do note that at one point or another there will be ISPs/networks that
are going to hit their prefix table sizes on their hardware. These will
start filtering aggressively on the assigned prefixes.

Greets,
Jeroen

9

What do you recommend to an end user that have a direct assignment of a
/48, and would like to disaggregate as part of a traffic engineering
strategy?

Moreiras.

10

Your TE is not the rest of the world's routing slot's problem. Get more
circuits and do your te with your providers directly.

-Blake

11

I accidentally sent this to nanog-request yesterday. I could use some feedback from anyone that can help, please.

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

12

Get another /48 for your other location.

Owen

13

Yes, from a filtering point of view a /48 in IPv6 is pretty similar to a /24 in IPv4, as perfectly illustrated by the two links in my post…

My point was that if you are getting the carrier to do the announcement for you then they can announce an aggregated /48 prefix and then break that up inside their network (if their internal policies allow it) to give the OP whatever prefix length per site they have decided on. The carrier only needs to carry the more specific prefixes on their backbone and the rest of the internet sees the aggregated prefix.

This all depends on the architecture of the OP’s network and what services they are buying from the carrier.

Of course, just getting a /48 per site and doing it properly would be the ideal scenario.

Edward Dore
Freethought Internet

14

Owen, thanks for this explanation. +1!

Eric Miller, CCNP
Network Engineering Consultant
(407) 257-5115