Subject: Re: [BEHAVE] The fragmentation issue

From: Xing Li <[email-masked]>
Date: Tue, 02 Jun 2009 07:11:50 +0800

Here are the algorithms currently implemented in a stateless
   translator (IVI), which works fine in the day-to-day operation.

   xing

         From IPv6 to IPv4:
         ----------------------------------------------------------
                         |     IPv6          |       IPv4
         ----------------------------------------------------------
         MTU             |     1500          |       1500
         ----------------------------------------------------------
         Fragmentation   |     DF=1          |   No ICMPv6 action.
         Handling        |                   |   Set DF=0 if the
                         |                   |   IPv6 packet is
                         |                   |   smaller than 1280
                         |                   |   and set DF=1 if
                         |                   |   the IPv6 packet
                         |                   |   is larger than
                         |                   |   1280.
                         ------------------------------------------
                         | Fragmentation     |   Fragmented
                         | header extension  |   packets
         ----------------------------------------------------------
         ICMP handling   | ICMPv6 (packet    |   ICMP (packet too
                         | too big)          |   big, the original
                         |                   |   advertised MTU-20)
         ----------------------------------------------------------

                        Figure 1: From IPv6 to IPv4

        From IPv4 to IPv6
        ----------------------------------------------------------
                        |     IPv4          |       IPv6
        ----------------------------------------------------------
        MTU             |     1500          |       1500
        ----------------------------------------------------------
        Fragmentation   |     DF=1          |   Send ICMP (packet
        Handling        |                   |   too big) to IPv4
                        |                   |   source address
                        |                   |   if the IPv4
                        |                   |   packet exceeds
                        |                   |   1480.
                        ------------------------------------------
                        |     DF=0          |   Fragment the IPv4
                        |                   |   packet so that it
                        |                   |   fits in 1280 byte
                        |                   |   IPv6 packet (with
                        |                   |   fragment header
                        |                   |   extension).
                        ------------------------------------------
                        | Fragmented        |   Fragmentation
                        | packets           |   header extension
        ----------------------------------------------------------
        ICMP handling   | ICMP              |   ICMPv6 (packet too
                        | fragmentation     |   big, the original
                        | needed but DF set |   advertised MTU+20).
                        |                   |   If the advertised
                        |                   |   MTU in "packet too
                        |                   |   big" message is
                        |                   |   smaller than 1280
                        |                   |   bytes, the value
                        |                   |   put into the
                        |                   |   translated "packet
                        |                   |   too big" message
                        |                   |   is 1280.
        ----------------------------------------------------------
        TCP MSS         | First SYN packet  |   Rewrites the MSS
        handling        |                   |   (MSS=MSS-20)
        ----------------------------------------------------------

                        Figure 2: From IPv4 to IPv6

---

From: Iljitsch van Beijnum <[email-masked]>
Date: Wed, 3 Jun 2009 18:23:47 +0200

>  translator (IVI), which works fine in the day-to-day operation.

This is not (very) different from what I've been suggesting.

Iljitsch

---

From: Xing Li <[email-masked]>
Date: Thu, 04 Jun 2009 13:25:02 +0800

> This is not (very) different from what I've been suggesting.
Very good. So we are actually agree on the fragmentation issues of the 
v4v6 translation.

xing

---

From: "Templin, Fred L" <[email-masked]>
Date: Thu, 4 Jun 2009 06:29:44 -0700

> -----Original Message-----
> From: Xing Li [mailto:[email-masked]]
> Sent: Wednesday, June 03, 2009 10:25 PM
> To: Iljitsch van Beijnum
> Cc: Templin, Fred L; Behave WG
> Subject: Re: [BEHAVE] The fragmentation issue
> 
> 
> 
> Iljitsch van Beijnum 写道:

I disagree; I made my case based on what the specs say.

Fred
[email-masked]

---

From: Xing Li <[email-masked]>
Date: Thu, 04 Jun 2009 22:27:52 +0800

> I disagree; I made my case based on what the specs say.

Could you please kindly mark the parts you disagree? Then we can modify
the working code and do test.
Thanks. xing

         From IPv6 to IPv4:

        From IPv4 to IPv6