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Re: draft-ooms-v6ops-bgp-tunnel-06.txt and v6ops review
MTU is not discussed in the draft, and I think MPLS carries some specific
issues that are worth describing. Basically, if the MTU in the MPLS core is
smaller than 1280, IPv6 packets greater than 1280 bytes are likely to be
Any chance (if this not too late) to add a small section/text on MTU handling
in the MPLS core ? (at lean the first sentence)
Here is a proposed text:
[IPv6] requires that every link in the internet have an MTU of 1280 octets or
greater. On MPLS links where no link-specific fragmentation and reassembly is
provided, MTU must be configured to have an MTU of at least 1280 octets plus
the encapsulation overhead in order for 6PE traffic to be forwarded.
(Add optionnaly the following text)
Some IPv6 hosts might be sending packets greater than the MTU available in the
IPv4 MPLS core and rely on Path MTU discovery to learn about those links.
Core routers are typically not IPv6 nodes and cannot build an IPv6 ICMP
"packet Too Big" message. Even if they can, they may not have knowledge of
the destination of the ICMP message and would be forwarding this message to
the egress PE, using mechaninsm described in [RFC3032].
According to [RFC2463], the ICMP "Packet too Big" message can be filled with
the invoking packet up to 1280 bytes. If any links on the path to the egress
PE has an MTU smaller than 1280, the ICMP message won't reach its
destination, preventing the originator of the traffic to be notified about
the MTU too small. This may cause significant operational problems; the
originator of the packets will notice that his data is not getting through,
without knowing why and where packets are discarded.
To minimize problems, it is advised to engineer the MTU on the ingress 6PE to
core interface, consistent with the core MTU, so that ICMP 'Packet too big"
can be sent by this router without these packets or the ICMP messages
entering the core MPLS.
On jeudi 9 Mars 2006 01:16, Fred Baker wrote:
> We have been asked to read and comment on
> "Connecting IPv6 Islands over IPv4 MPLS using IPv6 Provider Edge
> (6PE)", Jeremy De Clercq, 18-Jan-06, <draft-ooms-v6ops-bgp-
> which is about to go into IESG review. As you will recall, this has
> been round the block, and deserves speedy review. May I suggest that
> you get your comments in by 17 March at the latest. Reply to the
> authors copying idr; if you are not on the list, the working group
> chairs will deal with the moderation issues.