[Xorp-users] Fwd: Fwd: Problem in IPv6 SSM Multicast

[Pavlin Radoslavov]

> Yes, you are right. I ran tcpdump on the sender side and it appears the
> streaming server is sending out fragmented packets.

>From your logs below it appears that the second fragment is not
forwarded by the first router (Router 1), so you might want to
concentrate your effort on Router 1.

BTW, the reassembly of the fragments should happen on the receiver
side, so the routers in the middle should only forward the
fragments.

Regards,
Pavlin

> Streaming Server to Router 1:
> 
> 09:51:22.692158 IP6 (flowlabel 0x394e1, hlim 14, next-header: Fragment (44),
> length: 100) 2001:ec2:4002:fa11:200:24ff:fec4:3235 > ff3e::1234: frag
> (0xec6a52cc:1232|92)
> 09:51:22.700132 IP6 (flowlabel 0x394e1, hlim 14, next-header: Fragment (44),
> length: 1240) 2001:ec2:4002:fa11:200:24ff:fec4:3235 > ff3e::1234: frag
> (0xf753c59f:0|1232) 61541 > 1234: UDP, length 1316
> 09:51:22.700146 IP6 (flowlabel 0x394e1, hlim 14, next-header: Fragment (44),
> length: 100) 2001:ec2:4002:fa11:200:24ff:fec4:3235 > ff3e::1234: frag
> (0xf753c59f:1232|92)
> 09:51:22.708230 IP6 (flowlabel 0x394e1, hlim 14, next-header: Fragment (44),
> length: 1240) 2001:ec2:4002:fa11:200:24ff:fec4:3235 > ff3e::1234: frag
> (0xe37aa8b2:0|1232) 61541 > 1234: UDP, length 1316
> 09:51:22.708243 IP6 (flowlabel 0x394e1, hlim 14, next-header: Fragment (44),
> length: 100) 2001:ec2:4002:fa11:200:24ff:fec4:3235 > ff3e::1234: frag
> (0xe37aa8b2:1232|92)
> 09:51:22.716214 IP6 (flowlabel 0x394e1, hlim 14, next-header: Fragment (44),
> length: 1240) 2001:ec2:4002:fa11:200:24ff:fec4:3235 > ff3e::1234: frag
> (0xc1fd9920:0|1232) 61541 > 1234: UDP, length 1316
> 
> Apparently, a second fragment of length 100 is sent out after the first one.
> Oddly though.. once the fragmented packets reached Router 2, the second
> fragment is no longer received... probably dropped. I'm suspecting that
> Router 2 is unable to associate the second fragment to the first.
> 
> Router 1 <------> Router 2
> 
> 05:57:43.861774 IP6 (flowlabel 0xb063f, hlim 14, next-header: Fragment (44),
> length: 1240) 2001:ec2:4002:fa11:200:24ff:fec4:3235 > ff3e::1234: frag
> (0x40a52867:0|1232) 61542 > 1234: UDP, length 1316
> 05:57:43.871960 IP6 (flowlabel 0xb063f, hlim 14, next-header: Fragment (44),
> length: 1240) 2001:ec2:4002:fa11:200:24ff:fec4:3235 > ff3e::1234: frag
> (0x33f49657:0|1232) 61542 > 1234: UDP, length 1316
> 05:57:43.882756 IP6 (flowlabel 0xb063f, hlim 14, next-header: Fragment (44),
> length: 1240) 2001:ec2:4002:fa11:200:24ff:fec4:3235 > ff3e::1234: frag
> (0x2d938af5:0|1232) 61542 > 1234: UDP, length 1316
> 05:57:43.893746 IP6 (flowlabel 0xb063f, hlim 14, next-header: Fragment (44),
> length: 1240) 2001:ec2:4002:fa11:200:24ff:fec4:3235 > ff3e::1234: frag
> (0x62f4a589:0|1232) 61542 > 1234: UDP, length 1316
> 
> 
> Router <------> (sk0)receiver
> 
> 17:51:56.196244 IP6 (flowlabel 0xb063f, hlim 13, next-header: Fragment (44),
> length: 1240) 2001:ec2:4002:fa11:200:24ff:fec4:3235 > ff3e::1234: frag
> (0x48714108:0|1232) 61542 > 1234: UDP, length 1316
> 17:51:56.205162 IP6 (flowlabel 0xb063f, hlim 13, next-header: Fragment (44),
> length: 1240) 2001:ec2:4002:fa11:200:24ff:fec4:3235 > ff3e::1234: frag
> (0x5449397c:0|1232) 61542 > 1234: UDP, length 1316
> 17:51:56.214114 IP6 (flowlabel 0xb063f, hlim 13, next-header: Fragment (44),
> length: 1240) 2001:ec2:4002:fa11:200:24ff:fec4:3235 > ff3e::1234: frag
> (0x3e81a7bf:0|1232) 61542 > 1234: UDP, length 1316
> 
> I'm currently investigating this issue right now. Got to read more on IPv6
> fragmentation. hehe...
> 
> Thanks,
> Hansi