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

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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