Another MPLS MTU question - please delete thread

deleted.  I answered my own question

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  • My guess is the ethernet header = 14 bytes.

    On Thu, Feb 11, 2010 at 11:29 PM, awilkins <[email protected]> wrote:

    I have configured Inter-AS MPLS and have increased the 'mpls mtu' on ALL MPLS interfaces to 1524 bytes to test.  When I ping with a 1500 byte packet from one router to another with the df-bit set, the ping fails.  When I remove the df-bit, it works fine with no issues.

    My question is this:  Due to PHP and the size of the network, I should not have any more than one MPLS label on any path.  But, to make it conservative, let's assume I have two.  So, that means two labels = 8 bytes, so the MPLS MTU should be set to 1508 minimum.  Recall above that I set it to 1524.

    The following is an output of one of my router with 'debug mpls packet' enabled when pinging with a 1500 byte packet with the DF-Bit DISABLED:

    00:51:56: MPLS turbo: Fa1/0: rx: Len 1518 Stack {269 0 255} - ipv4 data

    Notice the Length of 1518 bytes.  Where the heck did 18 bytes come from?

    In this same output, I get the following that I can't say I fully understand:

    00:51:56: adj_switch_fragment: size 1522/14 ds at 0x792E91FC: CA030E3D 0008CA02 0E3D0008 8100 00638847
    00:51:56: adj_switch_fragment: maclen 18 ns at 0x792E920E: 0002E1FE 450005DC 00940000 FF01D189 D189A10E

    00:51:56: adj_switch_fragment: llen 4 dptr at 0x792E9212: 450005DC 00940000 FF01D189 A10E5573 557380D4
    00:51:56: adj_switch_fragment_ipv4_inline: size 1522/22 ds at 0x792E91FC: CA030E3D 0008CA02 0E3D0008 8100 00638847

    00:51:56: adj_switch_fragment_ipv4_inline: maclen 18 extra 4 ns at 0x792E9212: 450005DC 00940000 FF01D189 A10E5573 80D46CAD
    00:51:56: adj_switch_fragment_ipv4_inline: fsize 22 mp 92E91FC fe at 0x632EC530: CA030E3D 0008CA02 0E3D0008 81000063 88470002

    00:51:56: adj_switch_fragment_ipv4_inline: size 1502/22 ds at 0x792E9210: E1FE4500 05DC0094 0000FF01 D189 A10E5573
    00:51:56: adj_switch_fragment_ipv4_inline: maclen 18 extra 4 ns at 0x792E9226: 00003386 00270000 00000000 002F8C0C ABCDABCD

    00:51:56: adj_switch_fragment_ipv4_inline: mtu 1496 pak 632B7550
    00:51:56: adj_switch_fragment_ipv4_inline: ds 92E91FC ns 92E9212 ip 92E9212 es 22 fms 22 txs 66 ds 66
    00:51:56: adj_switch_fragment_ipv4_inline: size 66 ds at 0x092E91FC: CA030E3D 0008CA02 0E3D0008 8100 00638847

    00:51:56: adj_switch_fragment_ipv4_inline: fms 22 ip-fastmac at 0x092E91FC: CA030E3D 0008CA02 0E3D0008 8100 00638847
    00:51:56: adj_switch_fragment_ipv4_inline: ns at 0x092E9212: 4500002C 00942000 FE01B839 A10E5573 80D46CAD

    00:51:56: adj_switch_fragment_ipv4_inline: ds 9159A7E ns 9159A94 ip 9159A94 es 22 fms 22 txs 1498 ds 1498
    00:51:56: adj_switch_fragment_ipv4_inline: size 1498 ds at 0x09159A7E: CA030E3D 0008CA02 0E3D0008 8100 00638847

    00:51:56: adj_switch_fragment_ipv4_inline: fms 22 ip-fastmac at 0x09159A7E: CA030E3D 0008CA02 0E3D0008 8100 00638847
    00:51:56: adj_switch_fragment_ipv4_inline: ns at 0x09159A94: 450005C4 00940003 FE01D29E A10E5573 80D46CAD

    What does the size 1522/14 mean?  1522 bytes????  14 what?




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  • Or is ethernet 18 bytes (forgot the CRC).  And then are you pinging from the global or the vpn?

    On Thu, Feb 11, 2010 at 11:29 PM, awilkins <[email protected]> wrote:

    I have configured Inter-AS MPLS and have increased the 'mpls mtu' on ALL MPLS interfaces to 1524 bytes to test.  When I ping with a 1500 byte packet from one router to another with the df-bit set, the ping fails.  When I remove the df-bit, it works fine with no issues.

    My question is this:  Due to PHP and the size of the network, I should not have any more than one MPLS label on any path.  But, to make it conservative, let's assume I have two.  So, that means two labels = 8 bytes, so the MPLS MTU should be set to 1508 minimum.  Recall above that I set it to 1524.

    The following is an output of one of my router with 'debug mpls packet' enabled when pinging with a 1500 byte packet with the DF-Bit DISABLED:

    00:51:56: MPLS turbo: Fa1/0: rx: Len 1518 Stack {269 0 255} - ipv4 data

    Notice the Length of 1518 bytes.  Where the heck did 18 bytes come from?

    In this same output, I get the following that I can't say I fully understand:

    00:51:56: adj_switch_fragment: size 1522/14 ds at 0x792E91FC: CA030E3D 0008CA02 0E3D0008 8100 00638847
    00:51:56: adj_switch_fragment: maclen 18 ns at 0x792E920E: 0002E1FE 450005DC 00940000 FF01D189 D189A10E

    00:51:56: adj_switch_fragment: llen 4 dptr at 0x792E9212: 450005DC 00940000 FF01D189 A10E5573 557380D4
    00:51:56: adj_switch_fragment_ipv4_inline: size 1522/22 ds at 0x792E91FC: CA030E3D 0008CA02 0E3D0008 8100 00638847

    00:51:56: adj_switch_fragment_ipv4_inline: maclen 18 extra 4 ns at 0x792E9212: 450005DC 00940000 FF01D189 A10E5573 80D46CAD
    00:51:56: adj_switch_fragment_ipv4_inline: fsize 22 mp 92E91FC fe at 0x632EC530: CA030E3D 0008CA02 0E3D0008 81000063 88470002

    00:51:56: adj_switch_fragment_ipv4_inline: size 1502/22 ds at 0x792E9210: E1FE4500 05DC0094 0000FF01 D189 A10E5573
    00:51:56: adj_switch_fragment_ipv4_inline: maclen 18 extra 4 ns at 0x792E9226: 00003386 00270000 00000000 002F8C0C ABCDABCD

    00:51:56: adj_switch_fragment_ipv4_inline: mtu 1496 pak 632B7550
    00:51:56: adj_switch_fragment_ipv4_inline: ds 92E91FC ns 92E9212 ip 92E9212 es 22 fms 22 txs 66 ds 66
    00:51:56: adj_switch_fragment_ipv4_inline: size 66 ds at 0x092E91FC: CA030E3D 0008CA02 0E3D0008 8100 00638847

    00:51:56: adj_switch_fragment_ipv4_inline: fms 22 ip-fastmac at 0x092E91FC: CA030E3D 0008CA02 0E3D0008 8100 00638847
    00:51:56: adj_switch_fragment_ipv4_inline: ns at 0x092E9212: 4500002C 00942000 FE01B839 A10E5573 80D46CAD

    00:51:56: adj_switch_fragment_ipv4_inline: ds 9159A7E ns 9159A94 ip 9159A94 es 22 fms 22 txs 1498 ds 1498
    00:51:56: adj_switch_fragment_ipv4_inline: size 1498 ds at 0x09159A7E: CA030E3D 0008CA02 0E3D0008 8100 00638847

    00:51:56: adj_switch_fragment_ipv4_inline: fms 22 ip-fastmac at 0x09159A7E: CA030E3D 0008CA02 0E3D0008 8100 00638847
    00:51:56: adj_switch_fragment_ipv4_inline: ns at 0x09159A94: 450005C4 00940003 FE01D29E A10E5573 80D46CAD

    What does the size 1522/14 mean?  1522 bytes????  14 what?




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