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On Wed, Dec 02, 2009 at 07:25:02PM -0800, Scooter Morris wrote:
> OK, I've spent a bunch of time looking at this in more detail, and it
> looks like I've got an MTU/ICMP problem. Here is a tcpdump between a
> client and the cluster taken from the client:
>
> 19:09:42.102169 IP client.46508 > cluster.ssh: . 123430:126326(2896) ack
> 2318 win 190 <nop,nop,timestamp 1066530312 96022114>
> 19:09:42.102538 IP cluster > client: ICMP cluster unreachable - need to
> frag (mtu 1500), length 556
> 19:09:42.302789 IP client.46508 > cluster.ssh: . 91574:93022(1448) ack
> 2318 win 190 <nop,nop,timestamp 1066530513 96022114>
> 19:09:42.303138 IP cluster.ssh > client.46508: . ack 93022 win 479
> <nop,nop,timestamp 96022315 1066530513,nop,nop,sack 1 {94470:97366}>
> 19:09:42.303158 IP client.46508 > cluster.ssh: P 126326:129222(2896) ack
> 2318 win 190 <nop,nop,timestamp 1066530513 96022315>
> 19:09:42.303533 IP cluster > client: ICMP cluster unreachable - need to
> frag (mtu 1500), length 556
> 19:09:42.503791 IP client.46508 > cluster.ssh: . 93022:94470(1448) ack
> 2318 win 190 <nop,nop,timestamp 1066530714 96022315>
> 19:09:42.504147 IP cluster.ssh > client.46508: . ack 97366 win 479
> <nop,nop,timestamp 96022516 1066530714>
> 19:09:42.504168 IP client.46508 > cluster.ssh: . 97366:98814(1448) ack
> 2318 win 190 <nop,nop,timestamp 1066530714 96022516>
> 19:09:42.504176 IP client.46508 > cluster.ssh: . 98814:100262(1448) ack
> 2318 win 190 <nop,nop,timestamp 1066530714 96022516>
> 19:09:42.504528 IP cluster > lclient: ICMP cluster unreachable - need to
> frag (mtu 1500), length 556
> 19:09:42.704792 IP client.46508 > cluster.ssh: . 97366:98814(1448) ack
> 2318 win 190 <nop,nop,timestamp 1066530915 96022516>
> 19:09:42.705142 IP cluster.ssh > client.46508: . ack 98814 win 501
> <nop,nop,timestamp 96022717 1066530915>
> 19:09:42.705162 IP client.46508 > cluster.ssh: . 98814:100262(1448) ack
> 2318 win 190 <nop,nop,timestamp 1066530915 96022717>
> 19:09:42.705171 IP client.46508 > cluster.ssh: . 100262:101710(1448) ack
> 2318 win 190 <nop,nop,timestamp 1066530915 96022717>
> 19:09:42.705528 IP cluster > client: ICMP cluster unreachable - need to
> frag (mtu 1500), length 556
[snip]
> So, it looks to me like there is something going on the ICMP or the path
> MTU discovery between the client and the redirector, but this is using
> LVS-DR, so this shouldn't happen like it does with LVS-TUN, right? I've
> poured over the HOWTO and done several google searches, but the solution
> to this still eludes me. As another data point, this only happens when
> I scp data to the cluster, but when I pull data from the cluster using
> scp, I get great performance.
Hi Scooter,
this is very curious. It looks a lot like the problem detailed at [1]
that was reported a few months ago but IIRC the cause was never
completely diagnosed.
[1]
http://www.gossamer-threads.com/lists/lvs/users/22506?do=post_view_threaded#22506
I also suspect that something is going on with ICMP. It seems curious
that the client continues to send large (2896 byte) packets even after
receiving an ICMP message from the director (cluster).
* Are client and cluster on the same L2 (ethernet?) network?
* What is the MTU on the relevant interface on client
(and cluster for that matter).
* What OS is client running (out of interest)?
Ideally I'd like to try and reproduce the problem,
though IIRC I failed in that regard the last time this
problem was reported.
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