[mpls-linux-general] Re: MPLS stack observed using Ethereal analyzer !!

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There is currently a bug wit the MPLS stack that results in programs
like tcpdump and ethereal to see invalid packet when they are run on an LER.

Try running then from a host observing the traffic, nat participating in it.

Jim

On Tue, Jan 30, 2001 at 05:40:21PM -0600, Nanda, Debasis wrote:
> Hi James,
> 
> I have setup a small MPLS domain in our lab for testing using your
> implementation of linux-mpls.
> 
> I have the following configuration
> 
> (Please use prefix 168.219. for all ip address below )
> 
>         79.44	79.2	80.1     80.2	81.1	  81.2	82.2   82.45
>    --------        -------         ------           -------         --------
>   | Host 1 |------| LER 1 |-------| LSR 1|---------| LER 2 |-------| Host 2
> |
>    --------        -------         ------           -------         --------
>          eth0    eth2   eth0     eth0  eth1       eth0   eth2     eth0
> 
> 
> 
> 
> I observer that when a MPLS packet gets switched ( label swaping) in a LSR ,
> at the out port (interface) in either direction I get MPLS label stack . For
> example when a packet traverses from Host1 to Host 2 , it's label gets
> swaped at LSR 1. When I run Ethereal at LER2-eth0, I observer three MPLS
> heaser on each packet directed from LSR1 to LER2 . 
> 
> Frame 1 (102 on wire, 102 captured)
> Ethernet II
> MultiProtocol Label Switching Header
> MultiProtocol Label Switching Header
> MultiProtocol Label Switching Header
> Internet Protocol
> 
> A detailed packet dump is shown below along with the hex dump.
> 
> 
> 
> 
> Frame 1 (102 on wire, 102 captured)
>     Arrival Time: Jan 30, 2001 16:14:01.3064
>     Time delta from previous packet: 0.000000 seconds
>     Time relative to first packet: 0.000000 seconds
>     Frame Number: 1
>     Packet Length: 102 bytes
>     Capture Length: 102 bytes
> Ethernet II
>     Destination: 00:01:02:85:35:d5 (00:01:02:85:35:d5)
>     Source: 00:01:02:85:36:81 (00:01:02:85:36:81)
>     Type: MPLS label switched packet (0x8847)
> MultiProtocol Label Switching Header
>     MPLS Label: Unknown (282624)
>     MPLS Experimental Bits: 0
>     MPLS Bottom Of Label Stack: 0
>     MPLS TTL: 84
> MultiProtocol Label Switching Header
>     MPLS Label: Unknown (80032)
>     MPLS Experimental Bits: 0
>     MPLS Bottom Of Label Stack: 0
>     MPLS TTL: 0
> MultiProtocol Label Switching Header
>     MPLS Label: Unknown (258071)
>     MPLS Experimental Bits: 2
>     MPLS Bottom Of Label Stack: 1
>     MPLS TTL: 15
> Internet Protocol
>     Version: 10
>     Header length: 32 bytes
>     Differentiated Services Field: 0xdb (DSCP 0x36: Unknown DSCP; ECN: 0x03)
>         1101 10.. = Differentiated Services Codepoint: Unknown (0x36)
>         .... ..1. = ECN-Capable Transport (ECT): 1
>         .... ...1 = ECN-CE: 1
>     Total Length: 20268
>     Identification: 0xa8db
>     Flags: 0x04
>         .1.. = Don't fragment: Set
>         ..0. = More fragments: Not set
>     Fragment offset: 37224
>     Time to live: 8
>     Protocol: IPv6 hop-by-hop option (0x00)
>     Header checksum: 0x9e7b (incorrect, should be 0x6a3d)
>     Source: 197.8.105.0 (197.8.105.0)
>     Destination: reserved-multicast-range-NOT-delegated.example.com
> (231.74.119.58)
>     Options: (12 bytes)
>         Unknown (0xe0) (option length = 242 bytes says option goes past end
> of options)
> Data (44 bytes)
> 
>    0  0001 0285 35d5 0001 0285 3681 8847 4500   ....5.....6..GE. 
>   10  0054 138a 0000 3f01 750f a8db 4f2c a8db   .T....?.u...O,.. 
>   20  522d 0800 9e7b c508 6900 e74a 773a e0f2   R-...{..i..Jw:.. 
>   30  0100 0809 0a0b 0c0d 0e0f 1011 1213 1415   ................ 
>   40  1617 1819 1a1b 1c1d 1e1f 2021 2223 2425   .......... !"#$% 
>   50  2627 2829 2a2b 2c2d 2e2f 3031 3233 3435   &'()*+,-./012345 
>   60  3637 3435 3637                            674567           
> 
> 
> Where as wnen a packet from an LER to LSR is captured at the input interface
> of LSR ( ex.  packet travelling from LER2 to LSR1, captured at LSR1-eth0 )
> the dump is consistent with expected results as shown below
> 
> Frame 2 (102 on wire, 102 captured)
> Ethernet II
> MultiProtocol Label Switching Header
> Internet Protocol
> Internet Control Message Protocol
> 
> A detailed packet analysis along with the hex dump is provided below.
> 
> 
> Frame 2 (102 on wire, 102 captured)
>     Arrival Time: Jan 30, 2001 16:14:01.3067
>     Time delta from previous packet: 0.000337 seconds
>     Time relative to first packet: 0.000337 seconds
>     Frame Number: 2
>     Packet Length: 102 bytes
>     Capture Length: 102 bytes
> Ethernet II
>     Destination: 00:01:02:85:36:81 (00:01:02:85:36:81)
>     Source: 00:01:02:85:35:d5 (00:01:02:85:35:d5)
>     Type: MPLS label switched packet (0x8847)
> MultiProtocol Label Switching Header
>     MPLS Label: Unknown (20)
>     MPLS Experimental Bits: 0
>     MPLS Bottom Of Label Stack: 1
>     MPLS TTL: 254
> Internet Protocol
>     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: 84
>     Identification: 0x0000
>     Flags: 0x04
>         .1.. = Don't fragment: Set
>         ..0. = More fragments: Not set
>     Fragment offset: 0
>     Time to live: 254
>     Protocol: ICMP (0x01)
>     Header checksum: 0x8998 (correct)
>     Source: 168.219.82.45 (168.219.82.45)
>     Destination: 168.219.79.44 (168.219.79.44)
> Internet Control Message Protocol
>     Type: 0 (Echo (ping) reply)
>     Code: 0 
>     Checksum: 0xa67b (correct)
>     Identifier: 0xc508
>     Sequence number: 69:00
>     Data (56 bytes)
> 
>    0  0001 0285 3681 0001 0285 35d5 8847 0001   ....6.....5..G.. 
>   10  41fe 4500 0054 0000 4000 fe01 8998 a8db   A.E..T..@....... 
>   20  522d a8db 4f2c 0000 a67b c508 6900 e74a   R-..O,...{..i..J 
>   30  773a e0f2 0100 0809 0a0b 0c0d 0e0f 1011   w:.............. 
>   40  1213 1415 1617 1819 1a1b 1c1d 1e1f 2021   .............. ! 
>   50  2223 2425 2627 2829 2a2b 2c2d 2e2f 3031   "#$%&'()*+,-./01 
>   60  3233 3435 3637                            234567           
> 
> 
> 
> Could you please comment on this .
> 
> Regards
> 
> Debasis
> 
> 

-- 
James R. Leu