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

Victor Lyapunov victor.lyapunov at gmail.com
Sun Jun 8 09:10:11 EDT 2008

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>
> http://www.cisco.com/en/US/tech/tk175/tk15/technologies_tech_note09186a0080093bc7.shtml
> 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
> flexible.
> ------------------------------
> 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?
>  Hello
> I have a question regarding the ability to adapt the MTU for a PPPoE
> session.
> 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
> similar
> 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
> advertised
> by the LNS?
> Kind Regards
> ------------------------------
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