Subject: [pim] IPv6 Register Fragmentation

From: [email-masked]
Date: Tue, 18 May 2004 19:43:33 +0900

Hello,

I have a few comments regarding the Register message fragmentation in IPv6,
described as below in draft-ietf-pim-sm-v2-new-09.

    In IPv6, the DR MUST perform Path-MTU discovery, and an ICMP
    Fragmentation Required message MUST be sent by the encapsulating DR if
    it receives a packet that will not fit in the effective MTU of the
    tunnel.  If the MTU between the DR and the RP results in the effective
    tunnel MTU being smaller than 1280 (the IPv6 minimum MTU), the DR MUST
    send Fragmentation Required messages with an MTU value of 1280 and MUST
    fragment its PIM register messages as required, using an IPv6
    fragmentation header between the outer IPv6 header and the PIM Register
    header.

Here are my comments.

1) "ICMP Packet Too Big message" is appropriate rather than
   "ICMP Fragmentation Required message" in IPv6.

2) I believe that DR should not send ICMP Packet Too Big message
   when the original multicast packet is equal or smaller than
   the IPv6 minimum MTU. 
   The sender of multicast packets cannot send smaller packets,
   even if it has received such ICMP message. 

   I think IPv6 Register fragmentation should be treated the same as
   "IPv6 Tunnel Packet Fragmentation" described in RFC2473 Section 7.1.

   That is, ICMP "Packet Too Big" message should be sent by the
   encapsulating DR if the original IPv6 packet size is larger than
   the IPv6 minimum MTU. If the original IPv6 packet is equal or smaller
   than  the IPv6 minimum link MTU, DR must fragment its PIM register
   messages as required, using an IPv6 fragmentation header between
   the outer IPv6 header and the PIM Register header.

   IMHO, the encapsulating DR MAY fragment its register message whenever
   the original IPv6 packet size is larger than the effective tunnel MTU,
   and MAY not send ICMP "Packet Too Big" message.
   Because RP can process such fragmented register messages, and I think
   many implementations currently would works so. 

Any comments would be appreciated.

Best Regards,
Shiroko.

_______________________________________________
pim mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/pim