[Xorp-users] Re: Newbie Xorp & m'cast problem

[Dan Lukes]

edrt napsal/wrote, On 06/16/05 12:02:
>>	All messages come from 0.0.0.0, same MAC 0011.936d.61b2. All are IGMP 
>>leave, TTL=1, TOS=0xC0. All have the same destination - 
>>ALL-ROUTERS.MCAST.NET
...
>>	My theory:
>>Imagine there is only port on a switch subscribed to a group. The link 
>>on the port is going down with no IGMP LEAVE sent by station connected 
>>to it. The switch know that last subscriber of a group disapeared. So, 
>>it sends IGMP LEAVE by self. As it have no IP it uses 0.0.0.0 which mean 
>>"unknown source".

> Interesting, cause I'm working on IGMP snooping related stuff these days,
> I take time digging into this problem. Through experiment I find that
> if you unplug the wire connected to the multicast receiver, Cisco switch
> will send two IGMP leave to multicast routers
> 
>  - first IGMP leave message 
>     IP src   = multicast host
>     IP dst   = 224.0.0.2
>     IGMP grp = multicast group
> 
>  - second IGMP leave message
>     IP src   = 0.0.0.0
>     IP dst   = 224.0.0.2
>     IGMP grp = 0.0.0.0
> 
> The second IGMP leave message is actually originated from the STP ROOT switch
> to help the switching network quickly rebuilds the IGMP snooping entry after
> spanning tree reconfigures.

	"our" packets are diferend kind:
 >12:44:35.576909 igmp leave 224.2.255.237
 >12:44:35.579278 igmp leave 224.2.211.67

	E.g. IP src = 0.0.0.0, IGMP grp = multicast group

	In advance, STP is disabled on end-station ports, so UP/DOWN event on 
those interfaces shouldn't trigger an STP event. The bacbone topology 
isn't redundant and never changes, so it shouldn't be source of STP 
event also.

	Unfortunatelly, I can't identify the exact source of those packets. The 
prefix of the source MAC is Cisco's, but source MAC itself is not 
assigned to any port of any Cisco within our network ...

	I'm not sure, but it seems the source MAC is constant. I don't know if 
it's transmitted by one switch only or it's transmitted by any switch 
with special src MAC.

	In any case, the exact source is still unrevealed secret for me. It 
need futher investigation ...

							Dan