[152675] in North American Network Operators' Group
Re: What is a link-local address?? WAS: Re: JUNOS forwards IPv6
daemon@ATHENA.MIT.EDU (Jimmy Hess)
Tue May 8 00:27:29 2012
In-Reply-To: <CAP-guGWVhANrYv113pbAovSQbssqFr3Mo885eDNN_Jzb5t6irg@mail.gmail.com>
Date: Mon, 7 May 2012 23:26:55 -0500
From: Jimmy Hess <mysidia@gmail.com>
To: William Herrin <bill@herrin.us>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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
