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Re: IP4 address conservation method
From: Blake Hudson <blake () ispn net>
Date: Thu, 06 Jun 2013 09:29:56 -0500


Dan White wrote the following on 6/5/2013 9:44 AM:
On 06/05/13 00:34 +0200, Mikael Abrahamsson wrote:

I read:

http://www.nanog.org/sites/default/files/tues.general.Papandreou.conservation.24.pdf

I would like to point out RFC 3069. On most cisco equipment this is done using static routes and "ip unnumbered".

So my question is basically: What am I missing? Why can't data center guys not build their network the same way regular ETTH is done? Either one vlan per customer and sharing the IPv4 subnet between several vlans, or having several customers in the same vlan but use antispoofing etc (IETF SAVI-wg functionality) to handle the security stuff?

VLAN-per-subscriber (1 customer per VLAN), can require more costly routing equipment, particularly if you're performing double tagging (outer tag for switch, inner tag for customer). Sharing an IPv4 subnet among customers is
appropriate for residential and small business services, which is how we
typically deliver service. But may be less appropriate for larger business
customers (and I presume hosting customers) where the number of IPs is
large enough that you're throwing away less addresses ratio-wise. Generally
the simpler deployment model wins out in that type of scenario. Also, the
'ip unnumbered' approach may require some layer-3 security features.


One thing not mentioned so far in this discussion is using PPPoE or some other tunnel/VPN technology for efficient IP utilization. The result could be zero wasted IP addresses without the need to resort to non-routable IP addresses in a customer's path (as the pdf suggested) and without some of the quirkyness or vendor lock-in of using ip unnumbered.

PPPoE (and other VPNs) have many of the same downsides as mentioned above though, they require routing cost and increase the complexity of the network. The question becomes which deployment has more cost: the simple, yet wasteful, design or the efficient, but complex, design.

--Blake


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