[cisco-bba] How can Cisco CPE PPPoE MTU size adapt to MRU of LNS?

Frank Bulk - iNAME frnkblk at iname.com
Sun Jun 8 13:51:57 EDT 2008

Unless you manage all the CPE, too, I think configuring your LNs using "ip
mss adjust" is the safest way to accomplish wide-spread functionality.
Providing working PPP services generally results a lowest-common-denominator




From: cisco-bba-bounces at puck.nether.net
[mailto:cisco-bba-bounces at puck.nether.net] On Behalf Of Victor Lyapunov
Sent: Sunday, June 08, 2008 8:10 AM
To: Teague, Christopher J
Cc: cisco-bba at puck.nether.net
Subject: Re: [cisco-bba] How can Cisco CPE PPPoE MTU size adapt to MRU of


Hello Christopher


I was looking for a way that takes care of all types of traffic. I have seen
in previous IOS versions that

the pppoe-client requires the definition of a vpdn-group.


In the vpdn-group definition there is a command "ip mtu adjust"


vpdn-group PPPoE


  protocol pppoe

 ip mtu adjust 


I was hoping this to provide a solution but I was not able to test it


I am not sure how other CPEs (apart from Cisco) behave. At least when the

PPPoE session is initiated from my windows PC it does not take into account

the MRU of the LNS




On 6/8/08, Teague, Christopher J <Christopher.Teague at mybrighthouse.com>


I use the ip mss adjust command on the LNS to resolve MTU problems from my
CPEs, not exactly sure if this would help you or not but this seems pretty


From: Victor Lyapunov <victor.lyapunov at gmail.com>
Sent: Sunday, June 08, 2008 5:47 AM
To: cisco-bba at puck.nether.net <cisco-bba at puck.nether.net>
Subject: [cisco-bba] How can Cisco CPE PPPoE MTU size adapt to MRU of LNS?



I have a question regarding the ability to adapt the MTU for a PPPoE


>From the LNS side using the commands:


Virtual-template X

  ppp mtu adaptive


The LNS can apapt the length of the its MTU, according to the value set by
the CPE.


The question is how a cisco CPE (using IOS >= 12.4) can do the same, adapt

its MTU to the MRU value advertised by the LNS?


I am using cisco 1700 for CPE with IOS 12.4.  I could not find a command

to the "ppp mtu adaptive" that could be used inside the Dialer interface of
the PPPoE client.


Does anyone knows how can a CISCO CPE adapt its MTU to the MRU value

by the LNS?


Kind Regards



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