From: enginedrive2002 (enginedrive2002@yahoo.ca)
Date: Wed Oct 23 2002 - 12:36:05 GMT-3
Adam,
Thanks for your information.
Regarding command "router isis <a_number_here>", my understanding is like
yours, it's a process number. But if you check the IOS command reference,
the syntax is "router isis <area_tag>".
This comes with my confusion. The first thing I learn about IS-IS is "a
router is completely within an area, and the area borders are on links, not
on routers". If we could configure several "router isis <area_tag>" on a
single router, didn't it bread the rule above, which make the area border on
the routers? If we both accept the rule is true, would this make process
equal to area? Or the rule above is wrong in the very beginning?
Thanks!
E.D.
----- Original Message -----
From: "Adam Crisp" <adam.crisp@totalise.co.uk>
To: "enginedrive2002" <enginedrive2002@yahoo.ca>; <ccielab@groupstudy.com>
Sent: October 23, 2002 11:00 AM
Subject: RE: IS-IS area and process.
> should read at bottom of previous post:
> R1: NSAP net 39.826f.3142.0000.0000.0002.0006.0010.7b38.0001.00
> R2: NSAP net 39.826f.3142.0000.0000.0002.0007.0010.7b38.0002.00
> R3: NSAP#1: net 39.826f.3142.0000.0000.0002.0006.0010.7b38.00de.00
> R3: NSAP#2: net 39.826f.3142.0000.0000.0002.0007.0010.7b38.00de.00
> R3: NSAP#3: net 49.0001.0006.0010.7b38.00de.00
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Adam Crisp
> Sent: 23 October 2002 15:44
> To: enginedrive2002; ccielab@groupstudy.com
> Subject: RE: IS-IS area and process.
>
>
> Hi,
>
> It is possible to run more than one ISIS routing process on a router.
> This is a bit like running more that one OSPF process.
> Actually, you can run more that one ISIS process, but only one process can
> generate and maintain a Level-2 database.
> example:
>
> router isis 10
> !This runs as isis process with a process ID of 10
> !This is NOT an automonous system number - it's a process ID - and never
> leaves the router
> !this is is bit like typing 'router ospf 10'
>
> router isis 20
> !This runs as isis process with a process ID of 10
>
> router isis
> !This runs as isis process with a process ID of NULL - note that you
can't
> do this with OSPF
>
>
> The net statement under isis is a long number that is known as an NSAP
> address. This is a but like an X.500 address.
> this is described at
>
http://www.cisco.com/en/US/products/sw/iosswrel/ps1831/products_configuratio
> n_guide_chapter09186a008007fd45.html#1012605
>
> A very basic description of an NSAP address is:
>
> 1. AFI - Format Identifier - How long is the address, where are the byte
> boundaries atc.
> 2. IDI DFI AAI - Organisation - an attempt at describing the
organisation
> that holds the address
> 3. Domain - a number, a bit like autonomous system
> 4. Area - a number, a bit like an OSPF area ID
> 5. End system ID, a unique ID, can be anything but must be unique,
Ethernet
> MAC addresses are frequently used as these are already unique.
> 6. N-selector - a bit like TCP port number
>
> Different AFI's define different lengths, and different content of the
NSAP
> address. - ie picked from the list above
>
> eg AFI 49 - example 49.0001.0006.0010.7b38.00de.00
> AFI 49 - 49.aaaa.iiii.iiii.iiii.iiii.nn
> where a=area, i=systemID, n=N-sel
>
> eg AFI 39 - example net
39.826f.3142.0000.0000.0002.0006.0010.7b38.00de.00
> 39 net 39.idi .dfi .afi .dddd.aaaa.iiii.iiii.iiii.nn
>
> Does this answer your question?
>
> In practice, we are only intesested in two parts of the NSAP address,
> 1. Area
> 2. System ID
>
> more...
> Routing protocols - ISIS only exits on two levels
> Level-1 - can route between System ID's
> Level-2 - can route between Areas
>
> Level-3 - routing between domains.. well this doesn't exist, Cisco or
> somebody once thought up IDRP - Interdomain Routing Protocol - but this
was
> never implemented. - at least I've never seen it in an IOS release. My
guess
> is that the MBgp development will sort this out.
>
> As ISIS is only L1,L2 aware, we are only interested in AREA and SYSTEM_ID
> The area is all the NSAP address that is NOT the system ID. Therefore
>
>
> ISIS sees the NSAP as two parts, Area and System ID:
> NSAP: 39.826f.3142.0000.0000.0002.0006.0010.7b38.00de.00 will be treated
as:
> NSAP: 39.aaaa.aaaa.aaaa.aaaa.aaaa.iiii.iiii.iiii.00
>
> Back to level-1 again,
> In order for ISIS adjecencies to form, the area must be the same.
>
> It is possible for three different NSAPS to be configured on the same
> routing process
> eg.
> !
> router isis
> net 39.826f.3142.0000.0000.0002.0006.0010.7b38.00de.00
> net 39.826f.3142.0000.0000.0002.0007.0010.7b38.00de.00
> net 49.0001.0006.0010.7b38.00de.00
> !
>
> this has the effect of MERGING the areas together, therefore you could
have:
> R1---R2----R3, connected together with serial interfaces
> the following NSAP addresses configured:
> R1: NSAP net 39.826f.3142.0000.0000.0002.0006.0010.7b38.0001.00
> R2: NSAP net 39.826f.3142.0000.0000.0002.0006.0010.7b38.0002.00
> R3: NSAP#1: net 39.826f.3142.0000.0000.0002.0006.0010.7b38.00de.00
> R3: NSAP#2: net 39.826f.3142.0000.0000.0002.0007.0010.7b38.00de.00
> R3: NSAP#3: net 49.0001.0006.0010.7b38.00de.00
>
> Since r3 above merges the "areas" R1 and R2 WILL form an adjecency.
>
>
> Good luck
>
> Adam
>
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> enginedrive2002
> Sent: 23 October 2002 14:41
> To: ccielab@groupstudy.com
> Subject: IS-IS area and process.
>
>
> Hi, Group
>
>
> The concept of area and process in IS-IS really bothering me, sometimes
they
> look like the same, sometimes they are not. Could someone explain them to
> me?
>
> Thank you!
>
>
> E.D.
This archive was generated by hypermail 2.1.4 : Tue Nov 05 2002 - 08:35:54 GMT-3