ISP customer assignments

Chris Adams cmadams at
Wed Oct 14 02:49:57 UTC 2009

Once upon a time, Nathan Ward <nanog at> said:
> On 14/10/2009, at 2:14 PM, Chris Adams wrote:
> >What about web-hosting type servers?  Right now, I've got a group of
> >servers in a common IPv4 subnet (maybe a /26), with a /24 or two  
> >routed
> >to each server for hosted sites.  What is the IPv6 equivalent?  I can
> >see a /64 for the common subnet, but what to route for aliased IPs for
> >web hosts?  It is kind of academic right now, since our hosting  
> >control
> >panel software doesn't handle IPv6, but I certainly won't be putting
> >2^64 sites on a single server.  Use a /112 here again as well?  Use a
> >/64 per server because I can?
> Why route them to the servers? I would just put up a /64 for the web  
> servers and bind addresses to your ethernet interface out of that /64  
> as they are used by each site.
> I guess you might want to route them to the servers to save ND entries  
> or something on your router?

In the past, we saw issues with thousands of ARP entries (it has been a
while and I don't remember what issues now though).  Moving a block from
one server to another didn't require clearing an ARP cache (and
triggering a couple of thousand new ARP requests).

Also, it is an extra layer of misconfiguration-protection: if the IPs
are routed, accidentally assigning the wrong IP on the wrong server
didn't actually break any existing sites (and yes, that is a lesson from

Of course, with IPv4, you never assigned a large enough block to begin
with that would anticipate all growth, so routing additional blocks was
a lot easier than changing blocks, cleaner than secondary IPs
multiplying like crazy, etc., etc.  None of that would be an issue with
a single /64.

Chris Adams <cmadams at>
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.

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