netdev - Re: [PATCH] Fix bug of update IPv4 PMTU when received ICMP Fragmentation Needed message

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Date:	Sat, 02 Jun 2007 20:49:19 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	yjwei@...fujitsu.com (Wei Yongjun)
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] Fix bug of update IPv4 PMTU when received ICMP Fragmentation Needed message

Wei Yongjun <yjwei@...fujitsu.com> wrote:
> When received ICMP Fragmentation Needed message, PATH MTU is always set 
> to the 576 even if MTU in ICMP message is lager then 576. This is 
> because of error condition in function ip_rt_frag_needed(), now if 
> packet size of that ICMP message is less then new MTU, packet size will 
> be used ,but RFC says ICMP error message return as much as we can 
> without exceeding 576 bytes.
> 
> This patch has Fixed this BUG.
> 
> Signed-off-by: Wei Yongjun <yjwei@...fujitsu.com>
> 
> --- net/ipv4/route.c.orig       2007-05-25 05:22:47.000000000 +0800
> +++ net/ipv4/route.c    2007-06-01 11:42:55.000000000 +0800
> @@ -1424,7 +1424,7 @@ unsigned short ip_rt_frag_needed(struct 
>                            !(dst_metric_locked(&rth->u.dst, RTAX_MTU))) {
>                                unsigned short mtu = new_mtu;
> 
> -                               if (new_mtu < 68 || new_mtu >= old_mtu) {
> +                               if (new_mtu < 68) {
> 
>                                        /* BSD 4.2 compatibility hack :-( */

Huh? The test new_mtu >= old_mtu should only hold if the sending router
is buggy which is what the hack is for.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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