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Welcome to Cisco Support Community. We would love to have your feedback.

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Hall of Fame Super Bronze

Re: L2TP + IPSec, best way to avoid fragmentation

The best way to avoid fragmentation is for the MTU size on the communication to be less than the available MTU on the transit interfaces.

With TCP, you can use MSS and PMTUD as described on this article

http://www.cisco.com/en/US/tech/tk827/tk369/technologies_white_paper09186a00800d6979.shtml

As for UDP and other IP protocols that do not regulate their size based on MTU discovery, their packet will manually need to be reduced from the source and face fragmentation or drops while traversing the transit network.

New Member

Re: L2TP + IPSec, best way to avoid fragmentation

What is the best way to set MTU? Choices are: Fe4 (WAN), Virtual-PPP1 (L2TP session interface) or Vlan1 (LAN).

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