Subject: MTU changes

From: Sabrina Minshall <[email-masked]>
Date: Thu, 23 Dec 1999 12:30:39 -0800 (PST)

Hi,
  this pertains to PPP. If the MTU of an interface is changed after
  PPP has negotiated the MRU value should LCP state machine be
  restarted?

  Thanks,

  sabrina

---

From: "W. Mark Townsley" <[email-masked]>
Date: Sun, 26 Dec 1999 02:06:33 -0500

>   PPP has negotiated the MRU value should LCP state machine be

In general, yes. You could also be smart and only restart if the value
was decreased or some such. 

Of course, this is problematic at the LAC. In order to restart LCP, you
essentially have to restart the L2TP session as well. You could do this
transparently to the client, but it would be a bit tricky (e.g. offhand,
it would at least involve spoofing an LCP Confreq from the LAC to the
LNS or client). This is enough of an edge case that it is likely not
addressed specifically by most implementations.

Also, remember, the LAC must *always* be able to handle 1500 byte MRU,
and that this is all we are assured of at the LNS. Best to stay within
these limits.