[Linux-HA] glib: Unable to send bcast [-1] : Message too long

[emfau at t-online.de]

emfau at t-online.de schrieb:

> Guochun Shi schrieb:
> 
>>
>>>> OK, so bcast can work fine. Here is another test you can do, appy 
>>>> the attached patch to your tree. Configure and compile it
>>>> You will have a new test program in lib/comm. This test program load 
>>>> a communication plugin and send/recv messages.
>>>> usage:
>>>> comm -r -s -i <intval> -p <pluginname> -d <device> -z <pktsize> -c 
>>>> <num of packets>
>>>>
>>>> for example:
>>>> In the same machine,
>>>> receiver:
>>>> lib/comm/comm -s -i 1 -p bcast -d eth0 -c 10 -z 2048
>>>>
>>>> sender:
>>>> lib/comm/comm -r -p bcast -d eth0
>>>>
>>>> let me know how the test goes. thanks
>>>> -Guochun
>>>
>>>
>>>
>>>
>>> OK, I did two runs with z=1k and z=2k. Using 1k messages works fine, 
>>> 2k creates the "Message too long" error. Logs are attached.
>>
>>
>>
>> Can you find the exact message length that will not work, i.e with 
>> that that length-1 still works  fine ? That might give us some clue.
>>
>> My guess is some enviroment variables posed the message size limit on  
>> the module's send function, but I am not sure how exaxtly that can 
>> happen.
>>
>> -Guochun
> 
> 
> 'comm -s -p bcast -i 1 -d lnc1 -c 10 -z 1461' works fine, z=1462 fails.
> In case it matters, the output of z=1461 states
> 
> cluster[1392]: 2005/11/12_02:51:37 info: sending out a message 1472 bytes
> 
> but probably the difference of 11 bytes is just some sort of frame/header.

The problem seems to be related to the MTU setting. From the windows host

    ping node1 -f -l 1472

works ok, but

    ping node1 -f -l 1473

returns error "Packet needs to be fragmented but DF set". 'ifconfig' shows a 
MTU of 1500 for the interface so I'm not sure where and what to tweak to make 
this work, any idea?

Thanks,
   Michael