On 5/7/12, William Herrin <bill@herrin.us> wrote:
On 5/6/12, Matthew Petach <mpetach@netflight.com> wrote:
Which way do *you* vote? Hi Matthew, Cisco routers forward packets for 127.0.0.0/8 unless explicitly configured not to, treating it like any other unicast address.
The difference with IPv4, is the RFC1122 requirement is on hosts to not allow the network number { 127, <any> } to appear outside the host. There's no RFC requirement that a router refuse to forward traffic with a source or destination address within the reserved loopback network number. I a router filters based on source address it is an added feature. there's no rfc requirement that an IPv4 router "must not forward a packet with a source or destination address in the [IPv4] loopback range". The Cisco behavior for 127/8 with IPv4 is therefore quite reasonable. With IPv6, there is a RFC MUST requirement that such packets to the link local address space not be forwarded, therefore that Cisco behavior would be severely broken/ in IPv6 with regards to fe80::/10: an IPv6 router must not forward such packets as would be allowed with normal unicast addresses. (Even if the router is configured with one of those addresses, locally) -- -JH