Re: What is a link-local address?? WAS: Re: JUNOS forwards IPv6 link-local packets

[Jimmy Hess <mysidia () gmail com>]

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