nanog mailing list archives
Re: subnet prefix length > 64 breaks IPv6?
From: Bjørn Mork <bjorn () mork no>
Date: Sat, 07 Jan 2012 13:00:43 +0100
sthaug () nethelp no writes:
And yes, we know equipment that cannot *filter* on full IPv6 + port number headers exists (e.g. Cisco 6500/7600 with 144 bit TCAMs) - my original point was that I still haven't seen equipment with forwarding problems for prefixes > 64 bits.
Depends on what you consider a problem and whether you consider a layer 3 switch a "router" at all, but there are certainly some switches which will be more or less effective depending on prefix length. Ref e.g. http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_55_se/configuration/guide/swsdm.html#wp1257279 where you'll find this carefully worded hint: "Note: An IPv4 route requires only one TCAM entry. Because of the hardware compression scheme used for IPv6, an IPv6 route can take more than one TCAM entry, reducing the number of entries forwarded in hardware. For example, for IPv6 directly connected IP addresses, the desktop template might allow less than two thousand entries." Translated: "The stated numbers for IPv6 routes are twice the real max. However, prefix compression may give better utilisation under certain conditions". Bjørn
Current thread:
- Re: subnet prefix length > 64 breaks IPv6? Owen DeLong (Jan 03)
- Re: subnet prefix length > 64 breaks IPv6? Alexandru Petrescu (Jan 04)
- <Possible follow-ups>
- Re: subnet prefix length > 64 breaks IPv6? Owen DeLong (Jan 03)
- Re: subnet prefix length > 64 breaks IPv6? Karl Auer (Jan 03)
- Re: subnet prefix length > 64 breaks IPv6? Joel jaeggli (Jan 04)
- Re: subnet prefix length > 64 breaks IPv6? Bjørn Mork (Jan 07)
- Re: subnet prefix length > 64 breaks IPv6? sthaug (Jan 07)