Re: [Softwires] DS-Lite fragmentation RFC2473 reference

Francis Dupont <Francis.Dupont@fdupont.fr> Thu, 20 October 2011 09:27 UTC

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From: Francis Dupont <Francis.Dupont@fdupont.fr>
To: Daniel Roesen <dr@cluenet.de>
In-reply-to: Your message of Thu, 20 Oct 2011 09:42:31 +0200. <20111020074231.GA12499@srv03.cluenet.de>
Date: Thu, 20 Oct 2011 11:27:03 +0200
Sender: Francis.Dupont@fdupont.fr
Cc: softwires@ietf.org
Subject: Re: [Softwires] DS-Lite fragmentation RFC2473 reference
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 In your previous mail you wrote:

   Thanks for the clarification. Too bad the vendor landscape (both AFTR
   and B4) grossly ignore that normative requirement of RFC6333 and either
   fragment the payload instead of the tunnel,

=> there is a feature (not a bug as it is not incorrect) in some Linux
kernels which don't use the right MTU for the encapsulated packets
(there are some lines of code to remove, cf the PS).

Thanks

Francis.Dupont@fdupont.fr

PS: the patch (against an old version but this is not yet fixed in
recent kernels...):

*** /usr/src/linux/net/ipv6/ip6_tunnel.c	2008-07-13 23:51:29.000000000 +0200
--- ip6_tunnel+.c	2008-12-09 01:25:33.000000000 +0100
***************
*** 888,898 ****
  		mtu = IPV6_MIN_MTU;
  	if (skb->dst)
  		skb->dst->ops->update_pmtu(skb->dst, mtu);
- 	if (skb->len > mtu) {
- 		*pmtu = mtu;
- 		err = -EMSGSIZE;
- 		goto tx_err_dst_release;
- 	}
  
  	/*
  	 * Okay, now see if we can stuff it in the buffer as-is.
--- 888,893 ----