Labbing ODR
Djerk | 8 Aug 2007 13:32ODR (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
Categories: CCIE R&S, Main blog
2 Comments »
2 Responses to “Labbing ODR”
Hi buddy….ODR is an interesting topic. in your above post i cant get the clear picture of where those routers are positioned and how. I have one setup matching your description R5 hub(point-to-multipoint) , R2 R2 spokes. R5 is running ospf with R1, and running ODR with R2. Also R2 is running eigrp. So obviously as R2 is not a spoke anymore it wont receive the default route nor it will send its connected networks to R5. But assume if there was no igp running on spoke , how will making R5 R1 ospf area nssa affect the scenario ? will it have any effect on production of default route in ODR?
Thnx
Alex,
Interesting indeed 🙂 , ODR is often overlooked as a simple way of stub routing. Anyway, about your question; my test scenario did have R5 connected as OSPF nssa. With regards to ODR this doesn’t change a thing as ODR is not dependant upon OSPF, it just advertises a default route to the (ODR) stub router even if itself doesn’t have a default route. The curious thing to me was whether ODR was capable of advertising anything other than a default-route, as shown it can’t; there’s no need for more than the default for a stub router.
Which in turn bring me to the most likely reason that ODR isn’t normally used: If the stub router only has one route out (default-route) then why use ODR when you can use a static route and be independent from CDP. The answer I suppose would be that the stub router does advertise it’s routes and as such negates the need for a fully fledged routing protocol like RIP/EIGRP/OSPF or BGP.
I’m just thinking back to the ISP CPE considerations I had to make when at Easynet. Most prominently preventing us from using ODR was the lack of support of CDP over ATM. Though I seem to recall something about Cisco supporting that now, not sure if the non-cisco dslams etc. in the path would have. Pondering this a little longer I’m curious how to limit ODR route advertisement from the stub router, the CPE in case of (single homed) ISP terminology. I suppose this would be completely up to the PE, would this be controllable via Radius via av-pairs? Hmmm, will have to see if I can test that sometime somewhere…
Thank you for your post, admittedly I’ve not been very active here lately. Which will change soon as I really should get back to my studies soon… The matter of fact is that life has kinda claimed back most of my non work time after moving to the UK in January. Good to know the info here is still read and appreciated.
Djerk