127-Bit IPv6 Prefixes on Inter-Router Links with EOS (S-Series)?

[Erik_Auerswald]

Hi,

has anybody tried to implement /127 IPv6 transport networks with S-Series switches? Is some special configuration necessary for this to work?

The S-Series release notes list RFC 6164, Using 127-Bit IPv6 Prefixes on Inter-Router Links, as supported. I did not find any specific configuration advice in the manuals, GTAC Knowledge, or The Hub. Thus I simply configured a routable IPv6 address with /127 mask on the layer 3 interfaces, similar to using /31 networks with IPv4 (see RFC 3021). But after configuring the higher IPv6 address in the network, the switch answered to the lower IPv6 address as well, just as if the /127 network had a Subnet-router anycast address contrary to RFC 6164 section 6. This problem is described by RFC 3627, Use of /127 Prefix Length Between Routers Considered Harmful, which has been move to Historic status by RFC 6547, section 3.

Is any special configuration needed to use /127 subnets on the S-Series?

(I have tried to use /127 subnets inside a VRF on S-Series switches with firmware 8.42.05.0003)
(At a first look /127 subnets seem to work on EXOS.)

Thanks,
Erik

[Luke_French]

RFC 6164 is supported, so this should work. I believe it is a bug, can you open a case and include a show support and a trace showing the reply from the lower IP?

[Stephane_Grosj1]

Why do you want to use > 64 bit mask for IPv6? I don't see a valid reason for that. Don't try to replicate the IPv4 logic to IPv6 addressing, it leads you to painful problem...