From: Adam Crisp (adam.crisp@totalise.co.uk)
Date: Wed Oct 23 2002 - 13:51:48 GMT-3
NO,
the rule of a router being completely within an area is true of ISIS - OSI,
or TCP/IP is irrelevent.
I am sorry to confuse you with Multi ISIS processes, but I was trying to
explain why Cisco call the ISIS process the Area_tag.
The ISIS area changes on the wire, not withing the router.
You can run Multi-ISIS processes, but an interface can only exist within ONE
isis process.
The sentence " a router is completely within an area" could be written:
"A router is completly within an area and you enable which interfaces run
the ISIS protocol."
hope I haven't confused you.
You just need to remember:
1. Address the router, not the interfacs
2. LSA's are generated for each interface that is enabled for ISIS routing.
3. There are two sorts of adjecency:
3a. L1 is used between routers in the same Area
3b. L2 is used between routers in different Areas ( where area is not the
systems id - see way below!) and optionally between Routers in the local
Area.
4. L2 IP routes carry all IP information
5. L1 IP routes only carry IP information about the local ISIS area
6. If a router with a L2 database is a neigbour with a L1_ONLY router, then
it will inject a default router to the local ISIS topology
Enjoy ;-)
Adam
-----Original Message-----
From: enginedrive2002 [mailto:enginedrive2002@yahoo.ca]
Sent: 23 October 2002 17:30
To: Adam Crisp; ccielab@groupstudy.com
Subject: Re: IS-IS area and process.
Thank you very much, Adam!
It's getting clearer and clearer now. Based on your explanation, can I say
"the rule of a router is completely within an area is true for TCP/IP, but
false for CLNS"?
I have so little knowledge about CLNS, hope this conclusion doesn't sound
funny to you guys. :-)
E.D.
----- Original Message -----
From: "Adam Crisp" <adam.crisp@totalise.co.uk>
To: "enginedrive2002" <enginedrive2002@yahoo.ca>; <ccielab@groupstudy.com>
Sent: October 23, 2002 12:02 PM
Subject: RE: IS-IS area and process.
>
>
> yes, I see your problem.
>
> the Area Tag is definitely a Process ID.
> this is because if you were to have a router with more than one ISIS
routing
> process, then you would support more that one NSAP Area.
> eg
> !
> router isis 1
> net 49.0001.1111.1111.1111.00
> !
> router isis 2
> net 49.0002.1111.1111.1111.00
> is-type level-1
> !
> Router2#show clns
> Global CLNS Information:
> 0 Interfaces Enabled for CLNS
> NET: 49.0001.1111.1111.1111.00
> NET: 49.0002.1111.1111.1111.00
> Configuration Timer: 60, Default Holding Timer: 300, Packet Lifetime 64
> ERPDU's requested on locally generated packets
> Intermediate system operation enabled (CLNS forwarding allowed)
> IS-IS level-1-2 Router: 1
> Routing for Area: 49.0001
> IS-IS level-1 Router: 2
> Routing for Area: 49.0002
> Router2#
>
>
>
>
> This is all about OSI and network management
> ISIS can router OSI traffic - ie OSI clns
>
> OSI CLNS/CLNP is used in optical network management land, where devices
like
> Optical Add and Drop Multiplexors need to me managed, and the network
> protocol used is OSI - NOT TCP/IP!!
>
> The ADM's route OSI traffic between them using ISIS - and you can imaging
> that physically the devices can be hundreds of miles apart if they're
> connected via optical fibres.
>
> There is a limit to the number of Network Elements in any one Area, (ISIS
L1
> area) -
> The ADM network would therefore be split up into a number of L1 Areas.
>
> At some point the OSI traffic need to get back to a Network management
> center - and there is a gateway to a regular Cisco Router.
> Instead of having one router for every OSI Area (connected together via L2
> links), a Cisco router can support more that one Area (upto 26)
>
> More than one Area -------- More that one ISIS process
>
> hense the "router isis <area_tag>" ==== "router isis <process Id>
>
> In the scenario I've just tried to outline, the Cisco router would have a
L2
> link to the Telco's core network.
> Only one ISIS process can support L2 LSP's
>
> Hope this helps
>
> Adam
>
>
> -----Original Message-----
> From: enginedrive2002 [mailto:enginedrive2002@yahoo.ca]
> Sent: 23 October 2002 16:36
> To: Adam Crisp; ccielab@groupstudy.com
> Subject: Re: IS-IS area and process.
>
>
> 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.
>
> ______________________________________________________________________
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