Hi,
On 28 April 2016 at 10:46, Russell Coker via luv-main <[email protected]>
wrote:
> I've got a Linux system running remotely that has a strange TCP problem,
> when
> it sends (not receives) a large packet the connection hangs. For example
> if I
> ssh in and run commands with small amounts of output everything is fine,
> but if
> I run "ls -l /" then the connection hangs forever.
>
> My first thought was PMTU discovery, but "ping -M want -s 1400 8.8.8.8"
> works
> without any problems and also setting the MTU on the only Ethernet device
> to
> unusually low values (I tried as low as 400 bytes) didn't make any
> difference.
>
I would have tried a mtu that would need fragmentation.
1400 is unlikely to trigger fragmentation.
>From a host with Jumbo packet connectivity:
$ ping -M want -s 2000 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 2000(2028) bytes of data.
>From 113.197.15.115 icmp_seq=1 Frag needed and DF set (mtu = 1500)
2008 bytes from 8.8.8.8: icmp_seq=2 ttl=54 time=12.6 ms
2008 bytes from 8.8.8.8: icmp_seq=3 ttl=54 time=12.5 ms
2008 bytes from 8.8.8.8: icmp_seq=4 ttl=54 time=12.9 ms
> Any ideas as to what I should try next?
>
Probe to find the real path mtu is "ping -M do"
and see whether you get back an ICMP packet-too-big
or if the ICMPs get dropped somewhere.
>From home on ADSL
johnm@tower:~$ ping -M do -s 1472 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 1472(1500) bytes of data.
>From 150.101.154.1 icmp_seq=1 Frag needed and DF set (mtu = 1492)
ping: local error: Message too long, mtu=1492
ping: local error: Message too long, mtu=1492
ping: local error: Message too long, mtu=1492
johnm@tower:~$ ping -M do -s 1464 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 1464(1492) bytes of data.
1472 bytes from 8.8.8.8: icmp_seq=1 ttl=56 time=50.2 ms
1472 bytes from 8.8.8.8: icmp_seq=2 ttl=56 time=49.4 ms
1472 bytes from 8.8.8.8: icmp_seq=3 ttl=56 time=49.2 ms
Thanks,
John
> The system in question is a fairly standard AMD64 desktop PC running
> Debian/Jessie.
>
> --
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--
*John Mann*
Network Architect, Infrastructure Automation & Delivery
*Infrastructure Services, eSolutions*
​Monash University
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Clayton VIC 3168
Australia
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