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Re: IP4 address conservation method
From: Dan White <dwhite () olp net>
Date: Wed, 5 Jun 2013 09:44:14 -0500

On 06/05/13 00:34 +0200, Mikael Abrahamsson wrote:

I read:


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.

VLAN-per-service (>1 customer sharing a VLAN) is problematic, and typically
pushes a lot of IPv4 specific layer-3 security features (MACFF, DHCPv4
snooping, proxy arp, broadcast forwarding/split horizon) down into the
access equipment, and that's rarely a perfect feature set. In my
experience, IPv6 services lag behind on such equipment because those v4
security features break v6.

One vlan per customer also works very well with IPv6.


Dan White

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