[cisco-bba] Multilink PPP over L2TP

Oliver Boehmer (oboehmer) oboehmer at cisco.com
Wed Mar 3 03:49:04 EST 2004

> I guess what I'm driving at with the first question is that, will each
> individual member link count only the size fragment it sends and
> hence the total of all the member links should equal (within reason)
> the multilink bundle interface?

yes, should be, at least when it comes to byte count..
> Can IOS use the unique endpoint discriminator to tie calls into a
> multilink bundle before the authenticated username? (ie using the
> command "multilink bundle-name endpoint")

Yes, it can, but if ppp authentication is configured, IOS will always
authenticate first before forwarding the call.

Can't you do the address allocation on the LNS via local pools (possibly
downloaded from Radius)? If you're running low on IP addresses and can't
afford to provision large-enough pools for every LNS, maybe you can use
on-demand address-pools instead?


> -----Original Message-----
> From: Oliver Boehmer (oboehmer) [mailto:oboehmer at cisco.com]
> Sent: Tuesday, 2 March 2004 6:04 PM
> To: Ash Garg
> Cc: cisco-bba at puck.nether.net
> Subject: RE: [cisco-bba] Multilink PPP over L2TP
> Hi Ash,
> > Guys, I have tested this variety of multilink and connectivity seem
> > to be fine. However I have a few questions:
> > 
> > 1) Each session in the MLP bundle is given a virtual access
> > interface. What do the counters of this interface hold?
> what do you mean specifically? the multilink bundle interface (MLP
> bundle) sees IP packets, the individual member links only see the
> (possibly fragmented) MLP L2 packets (including PPP keepalives, etc.)
> > 2) Each ppp session is authenticated against the radius server when
> > it comes up. How can you get the router to send multilink attributes
> > (or something similar) to the RADIUS server so that it does not
> > allocate more dynamic IP address from its local pool which don't get
> > used?
> Unfortunately this is not possible. By the time the link is
> authenticated, IOS doesn't know yet if this is part of a multilink
> bundle. Forwarding a link (to join a multilink bundle, possibly on
> another LNS via multi-chassis multilink-ppp) happens after
> authentication phase.
> You can process the accounting packet (using the non-standard
> "Ascend-Num-In-Multilink" attribute 188) to see if this link is the
> first or a subsequent link in a bundle.
> 	oli

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