IPv6 woes - RFC

Mon Sep 20 12:15:50 UTC 2021

Owen DeLong wrote:

>> But, on routers, IPv6 costs four times more than IPv4 to look up
>> routing table with TCAM or Patricia tree.
>> 
>> It is not a problem yet, merely because full routing table of IPv6
>> is a lot smaller than that of IPv4, which means most small ISPs and
>> multihomed sites do not support IPv6.
> 
> Well, it’s a combination. Even with full v6 adoption, the routing
> table in v6 should be substantially smaller.

Not at all.

> Compare AS6939 v4 vs. v6:

That is not a meaningful comparison.

As mergers of ASes increases the number of announcements
and IPv4 addresses were allocated a lot earlier than those
of IPv6, comparing the current numbers of announcements is
not meaningful.

As a result, size of global routing table will keep
increasing unless there are other factors to limit it.

An important factor is that, for IPv4 with globally
routable /24, the absolute upper limit is merely 16M,
to be looked up by a single memory access of conventional
SRAM without needing TCAM. OTOH, IPv6 is hopeless.

Another favorite factor for IPv4 is that, though most of
routing table entries are generated from small entities
having a /24 assuming NAT, if such entities are merged,
renumbering is not so much a pain and they are motivated
to rely on a single /24 and sell others. OTOH, there is
no such motivation for IPv6.

> v4 is so thoroughly fragmented and v6 is a lot less likely to become
> so.

It is true that fragmentation is a problem. However, it merely
means that IPv6 address space will also be fragmented and that
IPv4 can but IPv6 can't be deployed at full scale,

						Masataka Ohta