[c-nsp] PPPoE termination on 2620

Robert E.Seastrom rs at seastrom.com
Mon Oct 11 17:16:52 EDT 2004

Dennis Peng <dpeng at cisco.com> writes:

>> Does a PPPoE(oE) interface eat one IDB, or two?  I'm doing some
>> similar stuff (running PPPoE(oE) on
>> non-supported-but-the-code-is-there platforms) and watching my CPU, so
>> I'm kinda curious...  "show idb" shows that it eats a hardware IDB,
>> but is there a software IDB in play too?
> It uses one hwidb and one swidb. The IDB limit applies to the swidb,
> and since the number of swidb is always equal or greater then hwidb's,
> swidb's are the ones you need to worry about.

So, I guess I'm unclear on the concept of IDBs - do hardware IDBs
exist in the shadow of the software IDB that is associated with the
interface, or am I getting that wrong?  Has anyone done a Powerpoint
for Networkers that shows how that part of the equation goes together?

Speaking of things that I may not be entirely right on, I've been
operating under the supposition that the majority of the sizing
equation for PPPoE terminations was the amount of bandwidth (both bps
and pps) one was pushing being the biggest deciding factor, with the
number of sessions one is terminating playing a minor (but possibly
non-linearly more significant as the number grows) role in terms of
resource exhaustion.  I've also assumed that this assumption is
correct not only in straight up PPPoE terminations but in LAC and LNS
L2TP terminations as well.  Am I off in the weeds here, or am I
substantially correct?

Any recommended reading, lessons-learned white papers, or anything of
that ilk would be appreciated.



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