[cisco-bba] LCP/MTU tuning template for LNS

Erich Hohermuth erich at hoh.ch
Thu May 8 14:29:38 EDT 2014

Hi Matt,

All these commands have diffrent aproaches for diffrent problems you
like to solve. While "lcp renegotiation on-mismatch” helps for interopt
issue with diffrent LAC vendors or diffrent endusertechnologies (ISDN,
AoATM, VoETH) on l2tp level, the "ppp mtu adaptive is only usefull if
your transfer links for l2tp and PPPoE supports a bigger MTU than 1500.
This is needed if you want to support MTU 1500 end to end for the
customer. This is mostly not supportet by wholesale partners for
diffrent reasons (political, operations and technical).

The command "tcp adjust-mss 1452" is a workaround for brocken clients if
you have to use a smaller mtu than 1500 which is mostly the case. There
was the early days of xDSL which we also had to clear the df-bit on
packets bigger than 1492 cause FW admins blocked all kind of icmp
packets including type 4 and 12. This is not longer needed in my opinion.

The performance question depends on your router model (72xx vs ASR) and
software version if you can build virtual subinterfaces or not.


Am 07.05.14 18:29, schrieb Matthew Melbourne:
> Service Providers’ LACs? What are users’ experiences of “lcp
> renegotiation on-mismatch” and MTU tuning under the virtual-template
> (e.g. ip tcp adjust-mss X and “ppp mtu adaptive”, etc)?

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