From: stefan vogt (stefan-uwe_vogt@web.de)
Date: Mon Mar 17 2003 - 19:54:08 GMT-3
David,
Many thanks for your detailed explanation. So I think the practical part of the question is answered. Maybe somebody can explain the theory, the 'protocol mechanics' behind this behavior...
-Stefan
"Voss, David" <dvoss@heidrick.com> schrieb am 17.03.03 23:41:43:
>
> Stephan,
>
> I'm sure Brian will give you an expert answer with regards to ISIS over NBMA
> hub and spoke, but I can offer you some good information based upon what
> I've tested in my lab.
>
> What is really boils down to is that if you are working with NBMA and ISIS
> your interface types (defined by ISIS as broadcast or point-to-point, read
> below) must match. If you are running hub and spoke, then you need to
> either fully mesh your frame-relay ISIS implementation or use point-to-point
> subinterfaces.
>
> In IS-IS there are two types of networks, point-to-point and broadcast.
> PHYSICAL = BROADCAST
> MULTIPOINT = BROADCAST
> POINT-TO-POINT = POINT-TO-POINT
>
> As first glance, you would think that if you created a hub and spoke NBMA
> network without subinterfaces, ISIS should work. But, there are problems as
> you will see.
>
> If I configure a hub and spoke ISIS implementation without using
> subinterfaces on any router, the spoke routers show the following:
>
> System Id Metric Next-Hop Interface SNPA
> Router --
> Router 10 Router Se0 DLCI 304
> Router 10
>
> Notice the missing Next-hop, Int, SNPA information above. No routes are
> being received by the other spoke either. As soon as I connect the hubs via
> frame map clns statements to create a full mesh, everything works fine:
>
> System Id Metric Next-Hop Interface SNPA
> Router --
> Router 10 Router Se0 DLCI 304
> Router 10 Router Se0 DLCI 305
>
> The same thing will happen if you configure your hub with a multipoint
> interface and keep the spokes as physical. ISIS treats physical interfaces
> as multipoint, so you may think it should work, but it does not. You must
> fully mesh.
>
> If you are not allowed/able to fully mesh, then an option is to create
> point-to-point connectivity between the hub and spokes.
>
> interface Serial0.2 point-to-point
> ip address 1.1.1.4 255.255.255.0
> ip router isis
> frame-relay interface-dlci 403
> interface Serial0.3 point-to-point
> ip address 1.1.5.4 255.255.255.0
> ip router isis
> frame-relay interface-dlci 405
>
> The problem is that once I do this on the hub, my interfaces on the hub
> ISIS-POINT-TO-POINT do not match the spokes ISIS-BROADCAST. So I have to
> change the spoke to become point-to-point.
>
> interface Serial0.1 point-to-point
> ip address 1.1.1.3 255.255.255.0
> ip router isis
> frame-relay interface-dlci 304
>
> Now that all interface-types match, everything looks fine on the spoke
> again.
>
> System Id Interface SNPA State Holdtime Type
> Protocol
> Router Se0.1 DLCI 304 Up 25 L1L2 IS-IS
> R3#sh isis top
>
> IS-IS paths to level-1 routers
> System Id Metric Next-Hop Interface SNPA
> Router --
> Router 10 Router Se0.1 DLCI 304
> Router 20 Router Se0.1 DLCI 304
>
> IS-IS paths to level-2 routers
> System Id Metric Next-Hop Interface SNPA
> Router --
> Router 10 Router Se0.1 DLCI 304
> Router 20 Router Se0.1 DLCI 304
>
> Gateway of last resort is not set
>
> 1.0.0.0/24 is subnetted, 2 subnets
> C 1.1.1.0 is directly connected, Serial0
> is directly connected, Serial0.1
> i L1 1.1.5.0 [115/20] via 1.1.1.4, Serial0.1
> 3.0.0.0/24 is subnetted, 1 subnets
> C 3.3.3.0 is directly connected, Loopback0
> 4.0.0.0/24 is subnetted, 1 subnets
> i L1 4.4.4.0 [115/20] via 1.1.1.4, Serial0.1
> 5.0.0.0/24 is subnetted, 1 subnets
> i L1 5.5.5.0 [115/30] via 1.1.1.4, Serial0.1
>
> Again, if you are running hub and spoke, then you need to either fully mesh
> your frame-relay ISIS implementation or use point-to-point subinterfaces.
>
>
>
> -----Original Message-----
> From: stefan vogt [mailto:stefan-uwe_vogt@web.de]
> Sent: Monday, March 17, 2003 2:53 PM
> To: Brian McGahan; ccielab@groupstudy.com
> Subject: Re: RE: ISIS and designated IS (DIS)
>
>
> Hello Brian,
>
> Many thanks for your answers. But your answer rises a new question for me:
>
> >As for Frame-Relay, IS-IS does not run over hub and spoke,
> > therefore DIS election is not really an issue.
>
> Why does IS-IS not run over hub and spoke?
>
> -Stefan
>
>
>
> "Brian McGahan" <brian@cyscoexpert.com> schrieb am 17.03.03 20:53:23:
> >
> > Stefan,
> >
> > The DIS in IS-IS is like the DR/BDR in OSPF. However, the DIS
> > election is preemptive, and there is no backup DIS. There is one DIS
> > per broadcast segment per level.
> >
> > To determine which router is the DIS, 'show clns is-neighbors'.
> > On a broadcast segment, the Circuit ID is the system ID of the DIS. In
> > addition to this, you can see the Pseudonode LSP in the ISIS database.
> > In the following example, there are two routers on a broadcast segment,
> > R1 & R6. DIS election is on a per level basis. Since R6 has a level-1
> > priority of 60, R1 is elected DIS for level-1 (R1 has default of 64).
> > However, since R6 has a level-2 priority of 70, it is elected DIS for
> > level-2.
> >
> > R6#sh run int e0/0
> > Building configuration...
> >
> > Current configuration : 142 bytes
> > !
> > interface Ethernet0/0
> > ip address 16.0.0.6 255.0.0.0
> > ip router isis
> > half-duplex
> > isis priority 60 level-1
> > isis priority 70 level-2
> > end
> >
> > R6#sh isis databas
> >
> > IS-IS Level-1 Link State Database:
> > LSPID LSP Seq Num LSP Checksum LSP Holdtime
> > ATT/P/OL
> > R6.00-00 * 0x00000002 0xCA67 1083 0/0/0
> > R1.00-00 0x00000004 0x9670 1054 0/0/0
> > R1.01-00 0x00000001 0xF2C9 1077 0/0/0
> > IS-IS Level-2 Link State Database:
> > LSPID LSP Seq Num LSP Checksum LSP Holdtime
> > ATT/P/OL
> > R6.00-00 * 0x00000001 0xF075 1078 0/0/0
> > R6.01-00 * 0x00000001 0x4F29 1079 0/0/0
> > R1.00-00 0x00000006 0xB681 1081 0/0/0
> > R6#
> >
> > For the level-1 link state database, you can see that R1
> > generates is own LSP as well as an LSP for the pseudonode, denoted by
> > the R1.01-00 LSPID. For level-2, R6 is the DIS, hence the LSPID of
> > R6.00-00 and R6.01-00.
> >
> > As for Frame-Relay, IS-IS does not run over hub and spoke,
> > therefore DIS election is not really an issue.
> >
> > For more info on DIS election:
> >
> > http://www.cisco.com/en/US/tech/tk472/tk474/technologies_tech_note09186a
> > 0080094b42.shtml
> >
> >
> > HTH
> >
> > Brian McGahan, CCIE #8593
> > Director of Design and Implementation
> > brian@cyscoexpert.com
> >
> > CyscoExpert Corporation
> > Internetwork Consulting & Training
> > Toll Free: 866.CyscoXP
> > Fax: 847.674.2625
> >
> >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> > Of
> > > stefan vogt
> > > Sent: Monday, March 17, 2003 9:20 AM
> > > To: ccielab@groupstudy.com
> > > Subject: ISIS and designated IS (DIS)
> > >
> > > Hi group,
> > >
> > > I have some questions regarding ISIS and designated IS (DIS).
> > >
> > > 1) I know that I can change the isis priority per interface. Is the
> > DIS
> > > eleceted per LAN segment or per area?
> > > 2) Is a DIS elected/required also for FR point-to-multipoint
> > connections?
> > > Which implications does this have to hub-and-spoke type
> > configurations?
> > > 3) What's the easiest way to figure out which router is elected as
> > DIS?
> > >
> > > Any input or link is appreciated.
> > >
> > > -Stefan
> > >
> > ________________________________________________________________________
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>
>
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