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