[quagga-users 7513] Re: Wireless group ospf problem

Ramon Navarro Bosch ramon at epsem.upc.edu
Mon Sep 11 14:18:35 IST 2006


I've found that the reason is loosing packages. Sometimes one side of
the net doesn't receive Hello packages and after some seconds I receive
a new one an act as it's a Init state ospf. I've seen that when I ping
to the other side of the wireless link sudently hello packages arrives
and Init state is begun, after some more seconds the link is on full
state but after some minutes hello packages doesn't arrive again from
one side and it looses routes again.

Can I do anything to network cards ( broadcom and madwifi ) or to quagga
configuration to improve this??

/Ramon


Matt Brown wrote:
> Ramon Navarro Bosch wrote:
>
>   
>>    All ospf links using wireless network interface fall each minuts.
>> I've done some tests: in some links if I ping from one site to the other
>> routes doesnt' disapear. On some links I've tried to look at show ip
>> ospf neibour and on some cases I see the routes but there is no new
>> route. I've also tried to use madwifi tunning tools but with no new
>> results. I've tried to use ip ospf retransmit-interval, hello-interval,
>> dead-interval without new results. I don't know if timers spf can help
>> me. I'm suspecting that for some reason I don't understand ospf
>> communication is not working beetwen wireless links. Do you know what
>> can I try ?
>>     
>
> One problem we have when diagnosing OSPF problems on our wireless links
> is that ICMP pings and other unicast traffic are not a good indicator of
> the packet loss that affects OSPF traffic. OSPF hellos are sent to the
> multicast address and hence are not acknowledged by the wireless layer,
> even though they're sent at basic rate this still makes them more
> susceptible to loss. So you can have a link that appears to have no
> packet loss but still drops a large proportion of your multicast packets.
>
> Turning up the OSPF timers can sometimes help with this, but of course
> it depends on what loss rates you're getting.
>
> I would suggest running a tcpdump on both ends of a link for a few
> minutes as a first step and see what packets are sent received. This
> will allow you to pinpoint (or eliminate) wireless layer loss as the
> cause of your problems.
>
> Cheers
>
>   
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