netdev - Re: Bug? GRE tunnel periodically won't transmit some packets

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Date:	Tue, 08 Nov 2011 07:43:26 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Chris Siebenmann <cks@...toronto.edu>
Cc:	netdev@...r.kernel.org
Subject: Re: Bug? GRE tunnel periodically won't transmit some packets

Le mardi 08 novembre 2011 à 01:17 -0500, Chris Siebenmann a écrit :
> | Le lundi 07 novembre 2011 à 11:21 -0500, Chris Siebenmann a écrit :
> | > I have a weird problem where a GRE tunnel periodically won't transmit
> | > some (TCP) packets, while at the same time it will transmit others just
> | > fine. This is happening in the current kernel.org git head kernel as
> | > well as earlier ones.
> [...]
> | Do you have any errors on :
> | 
> | ip -s -d link show dev greXXXX
> 
>  I do indeed. When the problem is happening, I see TX errors counting
> up one-for-one with packets that are not transmitted (and no RX
> errors). Otherwise I don't see any errors. The other end of the GRE
> tunnel shows no errors (TX or RX).
> 
>  Further information: when the problem is not happening, SSH doesn't
> seem to transmit 500-data-octet packets during startup. Instead I see:
> 
> 	IP 128.100.3.52.42538 > 128.100.3.51.ssh: Flags [.], seq 22:824, ack 22, win 91, options [nop,nop,TS val 1393299 ecr 29703771], length 802
> 
>  I have also once seen an 'ip route show table cache' entry for a route
> through the GRE tunnel with 552-byte MTU listed:
> 
> 	24.173.24.46 from 128.100.3.52 dev extun 
> 	    cache  expires 21333540sec ipid 0x9e5c mtu 552
> 
> I haven't been able to reproduce this. I have seen listed mtu figures
> in 'ip route show table cache' output routinely drop to 774, though.
> 
> (I would like to have more data on this but inconveniently the problem
> is now not reproducing itself. When it comes back I'll capture more
> information about route cache mtu values and error counts and see if
> there's anything interesting.)
> 

OK, but could you please report the exact "ip -s -d link gre..."
output ?



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