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

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Message-Id: <20111108070819.C643236221@apps0.cs.toronto.edu>
Date:	Tue, 08 Nov 2011 02:08:19 -0500
From:	Chris Siebenmann <cks@...toronto.edu>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Chris Siebenmann <cks@...toronto.edu>, 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).
[..]
| OK, but could you please report the exact "ip -s -d link gre..."
| output ?

Sure. Here it is:

7: extun: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1200 qdisc noqueue state UNKNOWN 
    link/gre 66.96.18.208 peer 128.100.3.58
    gre remote 128.100.3.58 local 66.96.18.208 dev ppp0 ttl inherit 
    RX: bytes  packets  errors  dropped overrun mcast   
    2793721    17015    0       0       0       0      
    TX: bytes  packets  errors  dropped carrier collsns 
    2242148    26824    18      0       0       0      

(The packet and byte counts were much lower when the problem happened;
this time around it happened relatively soon after I rebooted my machine
and brought up the PPPoE and GRE links, but hasn't happened since and
I've been using the GRE link.)

For vaguely historical reasons I don't use 'greXXX' as the name of
the GRE tunnel. I have a 'gre0' device, but it is not up. In case it
matters, its output is:

6: gre0: <NOARP> mtu 1476 qdisc noop state DOWN 
    link/gre 0.0.0.0 brd 0.0.0.0
    gre remote any local any ttl inherit nopmtudisc 
    RX: bytes  packets  errors  dropped overrun mcast   
    0          0        0       0       0       0      
    TX: bytes  packets  errors  dropped carrier collsns 
    0          0        0       0       0       0      

 Let me know if you want a full dump of 'ip link show' (with or
without verbosity).

	- cks
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