[mpls-linux-general] iptables problem?

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Hello all,

I have a question regarding iptables and mpls. I use four nodes (as in  
the MPLS for Linux example on the SF.net website), mpls version 1.962,  
FC8. The mpls packages are installed from the repository (so no custom  
patching etc). I try to filter the packets using iptables and mangle  
them so that they are directed onto an LSP, e.g.

sudo /sbin/mpls nhlfe add key 0 instructions push gen 1001 nexthop  
eth1 ipv4 10.0.0.2
(returns 0x2)
sudo /sbin/iptables -t mangle -A POSTROUTING -s 10.0.0.1 -d 10.0.0.10 - 
p tcp --source-port 4000 --destination-port 4001 -j mpls --nhlfe 0x2

At the downstream nodes, the label is swapped and finally removed at  
the last hop before the destination.
Now when I generate traffic (using d-itg), I see the following tcpdump  
at the first downstream node (10.0.0.2):

16:01:25.713116 MPLS (label 1001, exp 0, [S], ttl 64)
	IP (tos 0x0, ttl 64, id 22294, offset 0, flags [DF], proto TCP (6),  
length 564) 10.0.0.1.4000 > 10.0.0.10.4001: P 958977:959489(512) ack 1  
win 46 <nop,nop,timestamp 3001565 3070458>
16:01:25.713342 IP (tos 0x0, ttl 62, id 4498, offset 0, flags [DF],  
proto TCP (6), length 52) 10.0.0.10.4001 > 10.0.0.1.4000: ., cksum  
0xa1e4 (correct), ack 959489 win 5024 <nop,nop,timestamp 3070459  
3001565>
16:01:25.714115 MPLS (label 1001, exp 0, [S], ttl 64)
	IP (tos 0x0, ttl 64, id 22295, offset 0, flags [DF], proto TCP (6),  
length 564) 10.0.0.1.4000 > 10.0.0.10.4001: P 959489:960001(512) ack 1  
win 46 <nop,nop,timestamp 3001566 3070459>
16:01:25.714337 IP (tos 0x0, ttl 62, id 4499, offset 0, flags [DF],  
proto TCP (6), length 52) 10.0.0.10.4001 > 10.0.0.1.4000: ., cksum  
0x9fe2 (correct), ack 960001 win 5024 <nop,nop,timestamp 3070460  
3001566>
16:01:25.715116 MPLS (label 1001, exp 0, [S], ttl 64)
	IP (tos 0x0, ttl 64, id 22296, offset 0, flags [DF], proto TCP (6),  
length 564) 10.0.0.1.4000 > 10.0.0.10.4001: P 960001:960513(512) ack 1  
win 46 <nop,nop,timestamp 3001567 3070460>
16:01:25.715339 IP (tos 0x0, ttl 62, id 4500, offset 0, flags [DF],  
proto TCP (6), length 52) 10.0.0.10.4001 > 10.0.0.1.4000: ., cksum  
0x9de0 (correct), ack 960513 win 5024 <nop,nop,timestamp 3070461  
3001567>

However, when I change the source or destination port used by the  
traffic generator (or the protocol), then that traffic (which does not  
match the iptables rule), is still mapped onto the LSP (in this case  
the destination port is changed to 4002, but any other traffic to  
10.0.0.10 is in fact mapped onto the LSP).

16:11:31.590680 MPLS (label 1001, exp 0, [S], ttl 64)
	IP (tos 0x0, ttl 64, id 30521, offset 0, flags [DF], proto TCP (6),  
length 564) 10.0.0.1.4000 > 10.0.0.10.4002: P 1021953:1022465(512) ack  
1 win 46 <nop,nop,timestamp 3607443 3676339>
16:11:31.591011 IP (tos 0x0, ttl 62, id 46089, offset 0, flags [DF],  
proto TCP (6), length 52) 10.0.0.10.4002 > 10.0.0.1.4000: ., cksum  
0xeeb5 (correct), ack 1022465 win 5876 <nop,nop,timestamp 3676340  
3607443>
16:11:31.591681 MPLS (label 1001, exp 0, [S], ttl 64)
	IP (tos 0x0, ttl 64, id 30522, offset 0, flags [DF], proto TCP (6),  
length 564) 10.0.0.1.4000 > 10.0.0.10.4002: P 1022465:1022977(512) ack  
1 win 46 <nop,nop,timestamp 3607444 3676340>
16:11:31.592009 IP (tos 0x0, ttl 62, id 46090, offset 0, flags [DF],  
proto TCP (6), length 52) 10.0.0.10.4002 > 10.0.0.1.4000: ., cksum  
0xeca3 (correct), ack 1022977 win 5892 <nop,nop,timestamp 3676341  
3607444>
16:11:31.592681 MPLS (label 1001, exp 0, [S], ttl 64)
	IP (tos 0x0, ttl 64, id 30523, offset 0, flags [DF], proto TCP (6),  
length 564) 10.0.0.1.4000 > 10.0.0.10.4002: P 1022977:1023489(512) ack  
1 win 46 <nop,nop,timestamp 3607445 3676341>
16:11:31.593007 IP (tos 0x0, ttl 62, id 46091, offset 0, flags [DF],  
proto TCP (6), length 52) 10.0.0.10.4002 > 10.0.0.1.4000: ., cksum  
0xea90 (correct), ack 1023489 win 5909 <nop,nop,timestamp 3676342  
3607445>
16:11:31.593681 MPLS (label 1001, exp 0, [S], ttl 64)
	IP (tos 0x0, ttl 64, id 30524, offset 0, flags [DF], proto TCP (6),  
length 564) 10.0.0.1.4000 > 10.0.0.10.4002: P 1023489:1024001(512) ack  
1 win 46 <nop,nop,timestamp 3607446 3676342>
16:11:31.594005 IP (tos 0x0, ttl 62, id 46092, offset 0, flags [DF],  
proto TCP (6), length 52) 10.0.0.10.4002 > 10.0.0.1.4000: ., cksum  
0xe87e (correct), ack 1024001 win 5926 <nop,nop,timestamp 3676342  
3607446>

When I query the number of packets that match an iptables rule  
(iptables -t mangle -vnL), the query does not show any increment  
between after the second batch of traffic is generated (so according  
to the iptables output the packets that do not match the filter are  
not mapped onto the LSP, although in fact it DOES happen).

More interestingly, the incorrect behavior disappears after some  
time...so when I do not send packets from the source to the  
destination, the filtering recovers itself (until the packets are  
being send that do match the filter)...

I hope my question makes sense and someone can help me figure out the  
problem.

thanks
tom