Re: [mpls-linux-general] unexpected problems

[James R. L. <jl...@mi...>]

> An analysis with tethereal shows that the labelstack received on the last 
> node is not plain ip. tethereal still seems to recognize a mpls header and  
> shows a corrupt MPLS labelstack. The mpls header seems to be correct 
> except on the last node.

etherreal and tcpdump do not get a valid versionof the packet.  This is
a known bug.

Make sure you have IPv4 forwarding turned on on the last node other wise you
will lose the packet in the IPv4 stack.

Turn on MPLS kernel debugging by doing a 'mplsadm -d' then look at the 
kernel debuggin in your 'messages' log file or do a 'dmesg' and you will see
the output as well.

Jim

> 
> i.e.:
> tethereal seems to show on the node B a correct MPLS header.
> 
> Capturing on eth1 (the outgoing interface at node B):
> Frame 1 (56 on wire, 56 captured)
>     Arrival Time: Oct 30, 2001 13:12:10.817675000
>     Time delta from previous packet: 0.000000000 seconds
>     Time relative to first packet: 0.000000000 seconds
>     Frame Number: 1
>     Packet Length: 56 bytes
>     Capture Length: 56 bytes
> Ethernet II
>     Destination: 00:02:b3:1f:0b:a2 (00:02:b3:1f:0b:a2)
>     Source: 00:02:b3:1f:0b:96 (00:02:b3:1f:0b:96)
>     Type: MPLS label switched packet (0x8847)
> MultiProtocol Label Switching Header
>     MPLS Label: Unknown (99)
>     MPLS Experimental Bits: 0
>     MPLS Bottom Of Label Stack: 1
>     MPLS TTL: 255
> Internet Protocol, Src Addr: denise-3 (10.0.3.8), Dst Addr: 10.1.2.6
> (10.1.2.6)
>     Version: 4
>     Header length: 20 bytes
>     Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
>         0000 00.. = Differentiated Services Codepoint: Default (0x00)
>         .... ..0. = ECN-Capable Transport (ECT): 0
>         .... ...0 = ECN-CE: 0
>     Total Length: 35
>     Identification: 0x7d8f
>     Flags: 0x04
>         .1.. = Don't fragment: Set
>         ..0. = More fragments: Not set
>     Fragment offset: 0
>     Time to live: 64
>     Protocol: UDP (0x11)
>     Header checksum: 0xa42c (correct)
>     Source: denise-3 (10.0.3.8)
>     Destination: 10.1.2.6 (10.1.2.6)
> User Datagram Protocol, Src Port: 1024 (1024), Dst Port: 9876 (9876)
>     Source port: 1024 (1024)
>     Destination port: 9876 (9876)
>     Length: 15
>     Checksum: 0x91e5 (correct)
> Data (7 bytes)
> 
> Thanks in advance for new ideas solving this problem.
> 
> Andreas & Marc.
> 
> --------------------------
> University Of Paderborn
> 
> 
> 
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-- 
James R. Leu