ISIS - OSPF redistribution

[avosdo]

Hello everybody

We are currently running ISIS and recently we have purchased 2 WS-C3750X-24.

Unfortunately 3750 do not support ISIS and we have decide to use redistribution between ISIS and OSPF.

We are using Stack feature so consider 3750 as one chassis.            

Router A and Router B are ISIS neighbors. As first step we have setup redistribution between Router A and Switch 3750

Router A Configuration

router isis

net 49.0000.0000.0000.0001.00

metric-style wide

log-adjacency-changes

redistribute ospf 1 metric 100 match internal

router ospf 1

router-id 192.168.0.1

redistribute connected subnets

redistribute isis level-1-2 metric 30 subnets

passive-interface Loopback0

default-information originate always

redistribute ospf 1 metric 100 match internal

Switch 3750 Configuration

router ospf 1

router-id 192.168.2.1

passive-interface Vlan3

passive-interface Loopback0

interface Vlan3

ip address 192.168.10.65 255.255.255.224

ip ospf 1 area 0

From Router's A routing table we see the ospf routes life is good Switch routing table has E2 - OSPF external type 2 routes and is reachable from the rest of the network.

RouterA#show ip route ospf 1

Gateway of last resort is not set     

O        192.168.10.64/27 [110/2] via 172.17.1.3, 2d01h, GigabitEthernet1/20                          

                                     [110/2] via 172.17.1.1, 2d00h, GigabitEthernet1/19

When we bring up the ospf adjacencies with Router B the whole ISIS routes are replaced with E2 - OSPF external type 2 which is not desirable.

Router B Configuration

router isis

net 49.0000.0000.0002.00

metric-style wide

log-adjacency-changes

redistribute ospf 1 metric 100 match internal

router ospf 1

router-id 192.168.1.1

redistribute connected subnets

redistribute isis level-1-2 metric 30 subnets

passive-interface Loopback0

We have tried change the OSPF administrative distance from 115 to 120 on Switch and Router B and we have form routing loop.

In our scenario we would like the use the 2 routers A-B as default gateways for the switch and we also want the switch to advertise only the 192.168.10.64/27 subnet and not the routes learned from Router A.  

Please advise.

Regards

Antonis.     

[Muhammad Thanveer]

Hello Friend,

i am not sure about this but you can try it in a test scenario.

What I am thinking is when you redistribute the isis routes in to ospf you can tag them and stop them at router B.

Ex in router A

Router ospf 1

redistribute isis level-1-2 tag 11 subnets ( number after tag command can be <0-4294967295>  32-bit tag value, I have taken 11 here)

Now switch will learn all the isis routes in to ospf.

in Router B

There must be a route map and you can match the tag there

route-map deny-ospf-in deny 5

match tag 11

route-map deny-ospf-in permit 10

exit

router ospf 1

redistribute isis level-1-2 route-map deny-ospf-in subnets

by this we can avoid to learn the isis routes of Router A to be learnt by Router B via Ospf.

Please rate the post if you find informative.

Regards
Thanveer
"Everybody is genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is a stupid."

[Giuseppe Larosa · Accepted solution]

Hello Antonis,

sometimes too much information is simply too much.

There is no need to redistribute ISIS routes detail into the OSPF domain you just need to send a default route into OSPF domain to the 3750 stack and you have finished

On the other hand the OSPF route(s) have to be imported in core routing protocol ISIS to make them reachable from everywhere else in the ISIS domain.

So simply on each of RA, RB do

router ospf 1

no redistribute isis level-1-2 metric 30 subnets

Hope to help

Giuseppe

[Muhammad Thanveer]

Ha Ha Ha,

Nice Giuseppe,

Its done in a simple way.....!!!!

Regards
Thanveer
"Everybody is genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is a stupid."

[avosdo]

Giuseppe

You are right. Sometimes things are very simple.

I have made the changes that you have suggested and everything went well.

Many Thanks

Antonis.