Labbing ODR

 | 8 Aug 2007 13:32

ODR (On Demand Routing) is part of the R&S lab blueprint and the univercd has only one page on it. Can’t be too hard can it? Well that’s right but still it’s good to have done it once and see it in action. My first try failed as I didn’t know that ODR doesn’t work if there’s a routing protocol active on the stub router.

Some ODR characteristics:

  • Hub and spoke (stub) network
    • ODR is only enabled on the hub
    • Hub automatically advertises a default-route to the spoke
  • Uses CDP, so CDP neighborship must be established between hub and spoke
    • Enable CDP on F/R links and make sure the IP mappings support broadcasts
    • Vlans: Ensure that the routers can see each other rather than the switch they’re connected to (use l2protocol-tunnel or dot1q tunnelling)
  • No dynamic routing allowed on the spoke
  • Redistribution into ODR doesn’t work (not allowed)

My lab test:

R5 is an OSPF router connected via a NSSA (no-summary) area to some other routers. Be careful as even if R5 has no default-route ODR will advertise a default-route to R6 (the lab often explicitly prohibits default-routes). R5 and R6 are serially connected (HDLC) as I had trouble getting a l2protocol-tunnel working on my 3550, my 3548 doesn’t support l2protocol-tunnels.

R5 = C3661 ; R6 = C2691

Verify CDP on the interfaces:

C2691(config-if)#do sh cdp int
Serial0/0 is up, line protocol is up
_ Encapsulation HDLC
_ Sending CDP packets every 60 seconds
_ Holdtime is 180 seconds

C3661#sh cdp int s2/0
Serial2/0 is up, line protocol is up
_ Encapsulation HDLC
_ Sending CDP packets every 60 seconds
_ Holdtime is 180 seconds

Can they see each other?

C2691#show cdp nei s0/0 detail
-------------------------
Device ID: C3661
Entry address(es):
_ IP address: 10.1.56.5
Platform: Cisco 3660, Capabilities: Router Switch IGMP
Interface: Serial0/0, Port ID (outgoing port): Serial2/0
Holdtime : 135 sec
Version :
Cisco IOS Software, 3600 Software (C3660-IK9S-M), Version 12.4(10b), RELEASE SOFTWARE (fc3)
...

C3661#show cdp entry C2691
-------------------------
Device ID: C2691
Entry address(es):
_ IP address: 10.5.56.6
Platform: Cisco 2691, Capabilities: Router Switch IGMP
Interface: Serial2/0, Port ID (outgoing port): Serial0/0
Holdtime : 162 sec
Version :
Cisco IOS Software, 2600 Software (C2691-ADVENTERPRISEK9-M), Version 12.4(8c), RELEASE SOFTWARE (fc3)
...

Do they exchange routing information?

C2691(config-if)#do i
______ ...
______ o - ODR, P - periodic downloaded static route
Gateway of last resort is 10.1.56.5 to network 0.0.0.0
____ 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C _____ 10.1.6.6/32 is directly connected, Loopback0
C _____ 10.5.56.0/24 is directly connected, Serial0/0
o* _ 0.0.0.0/0 [160/1] via 10.1.56.5, 00:00:20

C3661(config-router)#do i
______ ...
______ o - ODR, P - periodic downloaded static route
Gateway of last resort is 10.1.25.2 to network 0.0.0.0
____ 10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
o _____ 10.1.6.6/32 [160/1] via 10.5.56.6, 00:00:16
C _____ 10.1.5.5/32 is directly connected, Loopback0
C _____ 10.1.25.0/24 is directly connected, Ethernet1/1
C _____ 10.1.56.0/24 is directly connected, Serial2/0
O*IA 0.0.0.0/0 [110/11] via 10.1.25.2, 00:06:51, Ethernet1/1

The stub router learned a default-route and the hub router learned the loopback interface of the spoke. I didn’t test the filtering of advertised and accepted routes. what I did trywas redistributing OSPF, statics and connected routes into ODR, this was not accepted:

C3661(config-router)#redistribute ospf 1 match internal
redistribution of "ospf" via "odr" not allowed

Hub configuration

Remember that the stub router has no ODR configuration.

C3661(config-router)#do srr
router odr
router ospf 1
_router-id 10.1.5.5
_log-adjacency-changes
_area 5 nssa
_network 10.1.25.5 0.0.0.0 area 5