Re: network hang trigger

[Peri Hankey <mpah@thegreen.co.uk>]

James

I can confirm that your problem occurs in xen-2.0-20040914. In this 
example a4.local is the xen0 machine (2.6.8.1-xen0), a30 is one of 
several xenU guests on a4  (all 2.6.8.1-xenU). First a simple ping, 
which works OK. Then your special poison ping: nasty pause, and possibly 
useful messages.

    [administrator@a30 administrator]$ ping a4.local
    PING a4.local (192.168.0.4) 56(84) bytes of data.
    64 bytes from a4.local (192.168.0.4): icmp_seq=1 ttl=64 time=5.72 ms
    64 bytes from a4.local (192.168.0.4): icmp_seq=2 ttl=64 time=0.150 ms

    --- a4.local ping statistics ---
    2 packets transmitted, 2 received, 0% packet loss, time 1010ms
    rtt min/avg/max/mdev = 0.150/2.937/5.724/2.787 ms
    [administrator@a30 administrator]$ ping -s 1473 a4.local
    PING a4.local (192.168.0.4) 1473(1501) bytes of data.

    ping: sendmsg: No buffer space available
    ping: sendmsg: No buffer space available
    ping: sendmsg: No buffer space available
    ping: sendmsg: No buffer space available
    ping: sendmsg: No buffer space available
    ping: sendmsg: No buffer space available
    ping: sendmsg: No buffer space available
     From 192.168.0.4 icmp_seq=1 Frag reassembly time exceeded
    1481 bytes from 192.168.0.4: icmp_seq=2 ttl=64 time=28980 ms
    1481 bytes from 192.168.0.4: icmp_seq=3 ttl=64 time=27980 ms
    1481 bytes from a4.local (192.168.0.4): icmp_seq=4 ttl=64 time=26980 ms

    --- a4.local ping statistics ---
    11 packets transmitted, 3 received, +1 errors, 72% packet loss, time
    29287ms
    rtt min/avg/max/mdev = 26980.569/27980.589/28980.612/816.525 ms, pipe 11

I hope that helps.
 
Peri

James Harper wrote:

>I have found that simply doing a ping with packetsize > 1500 (maybe
>mtu???) causes the network to hang for a short time. This is from xenU
>and xen0 on the same machine.
>
>Can someone else _please_ test this? I am able to make the network hang
>by saying from domU:
>ping -s 1473 <dom0 ip>
>(1473 + 28 byte header = 1501 byte packet)
>
>I'll do more testing tomorrow.
>
>thanks
>
>James
>
>
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