From: Sreeram P Bandakavi (sbandaka@xxxxxxxxx)
Date: Wed Sep 27 2000 - 18:30:14 GMT-3
Some theory on IDB hope this helps..
**********
You are limited by the total number IDBs allowed on the router which is
approximately
260 due to overhead. However, each physical interface and subinterface in
the router
also uses an IDB, so you need to subtract these from the 260. This number is
just
theoretical. The actual number also depends on how much memory you have and
how much
data you are going to transmit on each subinterface.
For example, if your serial port was running at T1 speed (1536KB) and all of
the remotes were 64KB circuits, you probably shouldn't go much above 24
subinterfaces, because if all sites tried sending at once, the T1 couldn't
handle all of the data.
http://www.cisco.com/warp/customer/105/39.html#odr_point this link gives
you some theoretical figures.
***********
Memory consumption for Frame Relay resources occurs in four areas:
1.Each data-link connection identifier (DLCI): 216 bytes
2.Each map statement: 96 bytes (or dynamically built map)
3.Each IDB (hardware interface + encap Frame Relay): 5040 + 8346 = 13,386
bytes
4.Each IDB (software subinterface): 2260 bytes
For example, a Cisco 2501 using two Frame Relay interfaces, each with four
subinterfaces, with a total of eight DLCIs, and
associated maps needs the following:
2-interface hardware IDB x 13,386 = 26,772
8-subinterface IDB x 2260 = 18,080 subinterfaces
8 DLCIs x 216 = 1728 DLCIs
8 map statements x 96 = 768 map statements or dynamics
The total is equal to 47,348 bytes of RAM used.
Note: The values used here are based on Cisco IOS Release 11.1 software.
Values for other releases may vary.
Sreeram
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Scott Morris
Sent: Wednesday, September 27, 2000 9:43 AM
To: 'Andrew'; ccielab@groupstudy.com
Subject: RE: IDB
It's like a memory matrix. In older models (2500's or so), there used to be
a hardware enforced limit of 300, as far as I know. In newer models, it is
solely based on the processor capabilities and the amount of memory
available. Obviously, the spiffier models with lots of memory will be able
to support more virtual interfaces than older models will.
IDB interfaces include any physical or virtual interfaces... So tunnels,
dialers, virtual-profiles, sub-interfaces, etc., etc., etc...
You can use "show idb" to give you an idea of what's up with your current
system. That's a hidden command still as far as I know.
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Andrew
Sent: Wednesday, September 27, 2000 11:45 AM
To: ccielab@groupstudy.com
Subject: IDB
Does anyone have a good description, explaination, or verbose documentation
on interface descriptor blocks? I know WHAT they are but I have never been
able to find a really good document on them, where they live, what makes
them the limiting factor in sub-interfaces, etc.
-Thanks
-A
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