IPv6 prefixes longer then /64: are they possible in DOCSIS networks?

Wed Nov 30 16:39:52 UTC 2011

On Wed, Nov 30, 2011 at 9:48 AM, Ray Soucy <rps at maine.edu> wrote:
> 1. Using a stateful firewall (not an ACL) outside the router
> responsible for the 64-bit prefix.  This doesn't scale, and is not a
> design many would find acceptable (it has almost all the problems of
> an ISP running NAT)

Owen has suggested "stateful firewall" as a solution to me in the
past.  There is not currently any firewall with the necessary features
to do this.  We sometimes knee-jerk and think "stateful firewall has
gobs of memory and can spend more CPU time on each packet, so it is a
more likely solution."  In this case that does not matter.  You can't
have 2^64 bits of memory.

You could make a firewall with the needed features (or a layer-3
switch), but it would have to be the layer-3 gateway of the subnets
you are protecting (not an upstream device) and it would need
knowledge of all addresses in use on the subnet, which must fit within
its ND table limits.  Only DHCP snooping can do this and customers are
not exactly keen on receiving DHCP-assigned addresses in mixed
datacenter environments, even if the addresses are static ones.  Once
you do that, you need to limit the number of addresses that can be
leased to each customer to far less than a /64 anyway.  All you gain
by having all that complexity is the appearance of bigger subnets,
when in reality, they are non-functional except for the limited number
of addresses which are actively leased out.

Again the arguments for /64 are not promising.  It is much less
complicated to simply deploy a longer subnet.

On Wed, Nov 30, 2011 at 11:13 AM, Jimmy Hess <mysidia at gmail.com> wrote:
> On Wed, Nov 30, 2011 at 8:48 AM, Ray Soucy <rps at maine.edu> wrote:
>> Saying you can mitigate neighbor table exhaustion with a "simple ACL"
>> is misleading (and you're not the only one who has tried to make that
>> claim).
>
> It's true, though, you can.
>
> From a network design POV, there may still be reasons to prefer the ACL method.
> They better be good reasons, such as a requirement for SLAAC on a large LAN.

No, Jimmy, you can't do that with SLAAC.  I do not think you
understand the problem.

-- 
Jeff S Wheeler <jsw at inconcepts.biz>
Sr Network Operator  /  Innovative Network Concepts