FR hub and spoke and ISIS

[ziutek]

Greetings to all:

I've got an interesting ISIS problem that I can't seem to solve.

Here's the situation, basic FR hub and spoke. Hub router (call it R1) is the DIS using the priority of 127, all routers are in the same area, and configured using the is-type level-1 command. Down each spoke there are two routers. The first spoke consists of one router (call it R2) connected to the hub using FR, and the next router down the spoke (R5) is attached using a serial HDLC connection. The other spoke uses all FR, R3 is conncted to R1 using FR subint multipoint, and R3 is attached to R4 using another subint multipoint. All routers have contacted their clns neighbor.

Here is the problem. Of course R1 has all routes in it's routing table. R2 only has R1 and R5 in it's table, and the same on the other spoke R3 has only R1 and R4. But, at the end of the spokes, on routers R4 and R5, both of these routers have routes to all routes in the network. Unfortunately R4 cannot ping R5 because the intermediate routers do not have routes to the other side ot the spoke, black-holing pings.

Now, if I take the is-type level-1 command off of R1, R2, and R3, which makes the default IS type both L1 and L2 for these three routers, all routes show up in the forwarding table for all three of these routers, the other spoke shows up as L2 routes, but only temporarily.

Below is a ping from R4 up the spoke to the hub, and down the other spoke to R5.

R4#ping

Protocol [ip]:

Target IP address: 10.5.5.1

Repeat count [5]: 1000

Datagram size [100]:

Timeout in seconds [2]:

Extended commands [n]:

Sweep range of sizes [n]:

Type escape sequence to abort.

Sending 1000, 100-byte ICMP Echos to 10.5.5.1, timeout is 2 seconds:

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.UU.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.UU.U.U.U.U.U.U.U

.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U.U

.U.U.U.U.U.U.UU.U.U.U.U.U.U.U.U.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Success rate is 46 percent (467/1000), round-trip min/avg/max = 200/380/1280 ms

As you can see, the routes in betwen disappear and then reappear. I'm geussing that they timeout?

Any thoughts on this would be seriously appreciated.

Joe

[ruwhite]

I would think they are flapping because of issues with the "blind terminal," being able to see LSP's from some attached IS' on what appears to be a broadcast link, and sometimes seeing those LSP's through a different direction, etc. IS-IS doesn't really support point-to-multipoint interfaces like this, and I don't know anyone who actually has gotten it to work, even using the priorities and such. The way the PSNPs and such work, I would think that it won't work.

:-)

Russ.W

[ziutek]

Thanks for the reply.

When the is-type level-1 is in place, I just find it very strange that the ends of the spokes can see all the routes in the network, but the router in between cannot. It can't be split horizon since the ends of the spoke see the updates. Any ideas why the intermediate routers would not install the routes from the other spoke?

Joe

[ruwhite]

Can you see the routes in the IS-IS database when it's configured as all level 1? Are the remote rotuers set to priority 0, or just the default?

Could you get the output of show isis data when it's all configured as level 1? As for the level 2 configuration, I would guess what's happening is that R1 receives R3's LSP, for instance, and installs it in it's table. It then sends out an SNP to make certain it's neighbors are sync'd, and finds that R4 doesn't have R3's LSP, so it drops those routes. When it receives a retransmitted LSP from R3, it again installs it, and the next time an SNP goes out from R1, the same thing happens again. In fact, I would venture to guess that this is a matter of R4 getting LSPs and SNPs destined for R3, rather than a strict problem with the DIS mechanism.

I'd just reconfigure the links to be point-to-point, which IS-IS supports.

:-)

Russ.W

[ziutek]

The spoek routers adjacent top the hub ae configured with a ptiority of 0.

The output from show isis dat is the same whether or not the three routers are L1 or L1/L2.

Configuring a full mesh between these three routers solves the problem, but then it's not really a hub and spoke topology.

I will configure the spokes with point-to-popint, and see how that works.

Once again thanks for your input.

Joe

[#6]

Joe,

I would be very interested to know if you ever gotthis working in a point-to-multipoint environment. I am working on the same problem and cannot seem to get this to work either. I get conflicting answers on whether a multipoint hub and spoke Frame relay configuration is supported with ISIS or not. There seems to be plenty of information indicating that it is supported.

[ziutek]

I never could get this to work. i ended up using point-to-point subinterfaces, and this seemed to work. I also got conflicting info about whether this is possible or not. Let me know if you find out ottherwise.

Joe

[msdonahue]

I have this running now and it works fine. I would take a look at the following link.

http://www.cisco.com/warp/public/97/isis-frint.html

If you have any other questions about this let me know.

[#9]

Do you have a frame relay network running point-to- multipoint with a full mesh, or hub and spoke? If you have it running in hub and spoke, how are your interfaces configured (physical or sub), and do you have inverse arp running at the hub or map statements? Same question on the remotes; map or inarp? The only way I was able to get this to work was with a full mesh environment. Then it didn't seem to matter if I had inarp or map statements.

[msdonahue]

I am runnning hub and spoke with inverse arp disabled. I am using Physical interfaces on most of the spoke routers with a few exceptions. On the Hub I am using Subs because I have a few different point-to-multi-point networks.

Here are my configs:

Hub:

interface Serial0

no ip address

encapsulation frame-relay

no frame-relay inverse-arp

frame-relay lmi-type ansi

!

interface Serial0.110 multipoint

ip address 189.18.110.2 255.255.255.248

ip router isis

frame-relay map clns 204 broadcast

frame-relay map clns 206 broadcast

frame-relay map ip 189.18.110.4 204 broadcast

frame-relay map ip 189.18.110.6 206 broadcast

no frame-relay inverse-arp

clns router isis

isis metric 31

isis password ciscoL2 level-2

isis hello-interval 30

!

router isis

net 8d.0000.0001.0002.00

summary-address 196.5.128.0 255.255.192.0

domain-password ciscodomain

Spoke 1:

interface Serial0/0

ip address 189.18.110.4 255.255.255.248

ip router isis

ip nbar protocol-discovery

encapsulation frame-relay

service-policy output CCIE

isis metric 31

isis password ciscoL2 level-2

isis priority 0

isis hello-interval 30

frame-relay map clns 402 broadcast

frame-relay map ip 189.18.110.6 402

frame-relay map ip 189.18.110.2 402 broadcast

no frame-relay inverse-arp

frame-relay lmi-type ansi

frame-relay ip rtp header-compression

!

router isis

net 00.0000.0001.0004.00

is-type level-2-only

domain-password ciscodomain

Spoke 2:

!

interface Serial0/0

no ip address

encapsulation frame-relay

no frame-relay inverse-arp

frame-relay lmi-type ansi

!

interface Serial0/0.110 multipoint

ip address 189.18.110.6 255.255.255.248

ip nat inside

ip router isis

isis metric 31

isis password ciscoL2 level-2

isis priority 0

isis hello-interval 30

frame-relay map clns 602 broadcast

frame-relay map ip 189.18.110.4 602

frame-relay map ip 189.18.110.2 602 broadcast

no frame-relay inverse-arp

!

!

router isis

summary-address 196.5.128.0 255.255.192.0

redistribute connected route-map IS-IS-R6

redistribute static ip

net 8d.0000.0001.0006.00

domain-password ciscodomain

[ziutek]

Could you possibly post the output from the sh isis topo command? Are you establishing only level-2 adjacencies? Does your routing table remain stable? I found that wne I initially started ISIS, the table would be fine, but after a couple of updates, it would get corrupted, and the other spoke route would disappear, almost as if Split horizon was preventing the updates from reaching the spokes.

Joe

[ziutek]

Maybe you could also post which IOS version and on which routers you have this working. This may or may not be a factor.

Joe

[msdonahue]

I am running 2621XMs with 12.3(4)T2 ENTERPRISE/SNASW PLUS IPSEC 3DES, image c2600-a3jk9s-mz.12.3-4.T2.

and 3745s with 12.3(4)T2 ENTERPRISE/SNASW PLUS IPSEC 3DES, image c3745-a3jk9s-mz.12.3-4.T2.

[ziutek]

Does this still work if all routers are in the same area? Of course then that pretty much means getting rid of your level-2 adjacencies only. Try putting all routers in one area with a common net, something like 49.0001.xxxx.xxxx.xxxx.00.

Joe

[ziutek]

Does this still work if all routers are in the same area? Of course then that pretty much means getting rid of your level-2 adjacencies only. Try putting all routers in one area with a common net, something like 49.0001.xxxx.xxxx.xxxx.00.

Joe