[c-nsp] ipv6 IOS SLB workaround question

[Alexander Clouter]

Dave <dcostell-cisconsp at torzo.com> wrote:
>
> Since the IOS SLB is not slated to work with IPv6 does anyone have any 
> ideas about a work around for this ? I was trying to figure out a way to 
> send traffic for a specific IPv6 address to a vserver IPv4 address, 
> anyone have any ideas ?
>
> For example:
> 
> DNS for www.slbtestsite.blah is 2001:db8::216
> the SLB vserver ip is 192.0.2.216
> 
> if someone hits www.slbtestsite.blah how could we map this space to use 
> the correct vserver and serverfarm to respond ?
> 
Depending on what your web clusters run, you could anycast[1] 
2001:db8::216 on a node or two of your webfarm (try to keep three router 
hops between them if possible) and then have 
Apache-mod_proxy/*inetd/Squid/etc loop back to your IPv4 SLB vserver 
address 192.0.2.216.

This would not be a 'least-conn' for the IPv6->IPv4 conversion, but that 
is a very low cost operation, as it's just gluing two TCP sessions 
together and shuffling opaque bits'n'bytes, I suspect you will not have 
any problems.

It is too early in the morning for me to think about if you could run 
into any nasty IPv4 ICMP corner cases; but I think you will be safe.

This would help you get by with using Cisco's IOS SLB, but this could be 
a sign that the writing is on the wall and it no longer is going to be 
meeting your needs.

Cheers

[1] http://www.digriz.org.uk/ha-ospf-anycast

-- 
Alexander Clouter
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