Another MPLS / VPLS MTU question

RouterOS General
1

Hi all,

I have a MPLS / VPLS question. I know these are quite common so apologies in advance

I have the following VPLS interface configured. ltmtu and advertised-l2mtu are configured to 1526 to allow for a 1500 byte frame + MPLS tag + Ethernet Header + VPLS Tag + PW Header -

/interface vpls
add advertised-l2mtu=1526 disabled=no l2mtu=1526 mac-address=\
    02:1A:40:02:78:A2 name=W01_Link remote-peer=10.0.0.102 use-control-word=\
    yes vpls-id=10:20 mtu=1500

I can’t ping the ‘next hop’ via the VPLS tunnel over 1500 Bytes, despite the packet only having an L2MTU of 1522 which seems logical-

[admin@STA02] /routing filter> / ping 10.10.10.102 do-not-fragment size=1501
  SEQ HOST                                     SIZE TTL TIME  STATUS
    0                                                         packet too lar...
    0 172.22.0.6                                576  64 0ms   fragmentation ...
    sent=1 received=0 packet-loss=100%

But I can ping a different hop via the VPLS tunnel over 1500 Bytes, albeit it’s being fragmented via MPLS-

[admin@STA02] /routing filter> / ping 10.0.0.101 do-not-fragment size=1522
  SEQ HOST                                     SIZE TTL TIME  STATUS
    0 10.0.0.101                               1522  63 6ms
    sent=1 received=1 packet-loss=0% min-rtt=6ms avg-rtt=6ms max-rtt=6ms

Is there something wrong with my understanding? Should the MTU=1500 setting on the VPLS interface not prevent this?

Thanks

2

Please could someone with a proven VPLS / MPLS network try pinging a remote hop with a size greater than the MTU set on the VPLS interface?

Thanks