From: Peter van Oene (pvo@usermail.com)
Date: Thu Oct 24 2002 - 09:59:00 GMT-3
Michael,
At 03:07 PM 10/23/2002 -0700, michael schwarz wrote:
>Does anyone know exactly what IOS feature set/version that supports
>multi-area isis? It seems 12.0 enterprise plus.... can anyone confirm?
I don't recall multi-area ISIS requiring any special train. However, I
can't say that I've ever used it either outside of labs.
>Am i correct in saying that the area-tag does not have any significance
>outside of an isis router- it merely is used to 'map' an interface to a
>particular NET address? And a router can run many of these NETs, either
>under the same process (area-tag), or under separate processes.
Area tag is used to differentiate multiple ISIS processes used on the same
router. Cisco actually supports 29 ISIS processes on the same box, with
all of them being L1 except for a single L2 (if required). Per level one
areas, the restrictions on NET's are as normal; ie unique sys-id per IS in
an area, and unique area-id per area. Each interface can only participate
in one area.
Per ISIS process, I believe the net limit of 3 areas still exists.
In summary, per process, you can assign up to 3 area IDs in 3 NETs, however
these areas will be considered as a single area (1 LSDB) from a routing
perspective. Per router, you can have up to 29 processes, and each will be
considered separately. IE the router itself would belong to 29 different
areas and maintain separate LSDBs per area.
Abe Martey in his new IS-IS book, "IS-IS Design Solutions" from Cisco
Press covers this pretty well. This usage though is really more CLNS
oriented and in IP networks, there is really little reason to use multi-area.
>It is the NET address alone, not the process/area-tag which is used to
>assign a link to an area. The first part of the NET identifies the area id,
>the latter part needs to be unique in the area as it identifies the "host"
>id. This is ALWAYS the case- atleast for any scenario you may see on the
>lab. Right?
Specifically, the tag in the interface command ip router isis <tag> refers
the interface to an ISIS process where the NET is found. Sys-ID's always
have to be unique per area, lab or otherwise.
>2 more questions to clear things up-
>When would you want to run multiple NETs under the same process?
When you are merging a networking, or otherwise migrating it from one area
addressing scheme to another. As long as to neighboring routers share at
least one Area-ID, they will form an adjacency and flood LSPs normal.
>And, if configuring multi-area isis MUST you configure multiple isis
>processes?
If you have devices that restrict the number of IS's in an area and you
need a given router to collect more devices than those devices would
support in a single area, then you would require multiple, distinct areas
which multi-area would support. In that case, yes, you need multiple
processes with unique Area-IDs.
>----- Original Message -----
>From: "Adam Crisp" <adam.crisp@totalise.co.uk>
>To: "enginedrive2002" <enginedrive2002@yahoo.ca>; <ccielab@groupstudy.com>
>Sent: Wednesday, October 23, 2002 9:51 AM
>Subject: RE: IS-IS area and process.
>
>
> > 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.
> > >
> > > ______________________________________________________________________
> > Post
> > > your free ad now! http://personals.yahoo.ca
> >
> > ______________________________________________________________________
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