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Re: [Pppext] Re: Last Call: 'Accommodating an MTU/MRU greater than 1492 in PPPoE' to Informational RFC

2006-02-21 13:37:44
Pekka Savola writes:
This doc seems to define a PPPoE option 'PPP-Max-Payload'.  It talks 
of using PPP MRU option.  There is no PPP MTU option that I could see.

My question here is, should there be a PPP MTU option instead of a 
PPPoE option?  This would be a more generic solution to this part of 

I don't follow.  PPP is symmetric -- there are two MRUs negotiated,
one for each direction.  Your peer's MRU is your maximum (and default)
MTU.

How could we need another option for this?  Or how could one help?

What's really going on here is negotiation about the existence of a
usable path.  Unfortunately, the underlying protocol itself (other
than LLDP) doesn't provide a way to do this.  This new mechanism thus
doesn't solve the actual problem, but does at least allow consenting
peers to identify each other.  (In other words, I view it as just a
boolean.)

MRU test procedure using MRU-sized Echo-Requests is disabled by 
default and to be used for debug purposes only.  I'm questioning 
whether this is wise.  The protocol would be much more robust against 

I don't think it is.  But we did discuss that during the document
review.

==> first off, a major clarification request:  RFC1661 does not 
mention 'MTU' anywhere,

It doesn't need to, I think.

-- 
James Carlson, KISS Network                    
<james(_dot_)d(_dot_)carlson(_at_)sun(_dot_)com>
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

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