From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Siebenmann Subject: Re: Bug? GRE tunnel periodically won't transmit some packets Date: Tue, 08 Nov 2011 01:17:37 -0500 Message-ID: <20111108061737.B04D236221@apps0.cs.toronto.edu> References: <1320684905.2361.25.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Chris Siebenmann , netdev@vger.kernel.org To: Eric Dumazet Return-path: Received: from cliff.cs.toronto.edu ([128.100.3.120]:60537 "EHLO cliff.cs.toronto.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751234Ab1KHGRi (ORCPT ); Tue, 8 Nov 2011 01:17:38 -0500 In-reply-to: eric.dumazet's message of Mon, 07 Nov 2011 17:55:05 +0100. <1320684905.2361.25.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC> Sender: netdev-owner@vger.kernel.org List-ID: | Le lundi 07 novembre 2011 =C3=A0 11:21 -0500, Chris Siebenmann a =C3=A9= crit : | > I have a weird problem where a GRE tunnel periodically won't transm= it | > 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 a= s | > well as earlier ones. [...] | Do you have any errors on : |=20 | 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 2= 2, 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=20 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.) - cks