> -----Original Message----- > From: James Carlson [mailto:james.d.carlson@xxxxxxx] > Sent: Monday, February 20, 2006 10:50 AM > To: Pekka Savola > Cc: pppext@xxxxxxxx; iesg@xxxxxxxx; ietf@xxxxxxxx > Subject: Re: [Pppext] Re: Last Call: 'Accommodating an MTU/MRU greater > than1492 in PPPoE' to Informational RFC > > Pekka Savola writes: > > I guess the problem I was having here is that I didn't understand why > > a PPPoE MTU options would be useful (still don't). After all, if both > > PPP endpoins would signal MRU = 2000 (for example), then PPPoE could > > just use that with no need for an extra option? Looking back at the > > archives, it appears others have had related concerns, so I guess this > > is beating a dead horse.. > > I think it is. What's really needed is some end-to-end mechanism > within 802 itself for making sure that the MTU on the path is > correct. That mechanism doesn't really exist. > > There are several problems here. First of all, there are several > PPPoE implementations that will assume a fixed limit of 1492 (based on > requirements of the 802 the standards), no matter what PPP attempts to > negotiate. So merely having the LCP MRU option show something larger > won't help -- the peer already "knows" that the path can't possibly be > that wide. > > Now, it'd be reasonable to have LCP negotiate an MRU > 1492, and then > use LCP Echo-Request (in parallel with IPCP start-up) to verify that > the path really supports packets that large. If it doesn't, then > restart LCP and negotiate a fixed 1492. That wouldn't require any > protocol changes at all. That can be done but then that means for PPPoE sessions to go beyond 1492 BRAS always have to incur this cost of verification; as BRAS may not be able to turn off that verification selectively either as it wouldn't be certain which clients really are asking for 1500 MRU (due to underlying network really supporting it) or which are asking 1500 MRU due to their config/implementation being broken. Seems fixing these broken clients would be a much overhead for Service provider. Veera > > I think something like that is what you're suggesting. It seems > reasonable to me, except that I think the draft authors wanted > explicit signaling between the peers to enable the new mode of > operation. > > -- > James Carlson, KISS Network <james.d.carlson@xxxxxxx> > Sun Microsystems / 1 Network Drive 71.232W Vox +1 781 442 2084 > MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677 > > _______________________________________________ > Pppext mailing list > Pppext@xxxxxxxx > https://www1.ietf.org/mailman/listinfo/pppext _______________________________________________ Ietf@xxxxxxxx https://www1.ietf.org/mailman/listinfo/ietf
