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Cell Relay Retreat>MPLS-OPS Archive>month:2003-Jul> msg00140



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RE: L2 VPN over MPLS

  • From: sthaug@nethelp.no
  • Date: Tue, 29 Jul 2003 15:51:23 +0200
  • Cc: mpls-ops@mplsrc.com
  • Resent-Date: Tue, 29 Jul 2003 10:18:11 -0400
  • To: elkou141061@hotmail.com

> The service is L2 VPN (Martini ) so 2 label plus the control word .

And if you want to use your L2VPN to transport Ethernet, the Ethernet
frame itself may be up to 1518 bytes (14 bytes header + 1500 bytes data
+ 4 bytes CRC). Thus you need a minimum MTU of 1518 + 2*4 (labels) + 4
(control word) = 1530 bytes.

This is easy enough to verify if you have a suitable lab setup with
for instance POS links (Cisco default MTU 4470). Setting your MPLS
MTU ("tag-switching mtu" in Cisco speak) to 1530 bytes will let full
sized Ethernet frames through with EoMPLS - setting it to 1526 will
block them.

Steinar Haug, Nethelp consulting, sthaug@nethelp.no

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