From: Adam Crisp (adam.crisp@totalise.co.uk)
Date: Wed Oct 23 2002 - 12:00:55 GMT-3
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.
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