The RID is the dotted decimal value by which other OSPF routers will identify a given OSPF router. There are some interesting defaults for this value, and a command you should know to hardcode the RID. You had also better know what has to happen for this command to take effect, so let's take a more detailed look at the OSPF RID.
In this example, R1 has an adjacency with R2 and R3 over the 172.12.123.0/24 frame network. R1 is the hub, with R2 and R3 as the spokes. No other interfaces are OSPF-enabled on any of the routers. Running show ip ospf neighbor on R1, we see some unusual values under "Neighbor ID", which is another name for the OSPF RID.
Notice the Neighbor ID of each remote address is the loopback address. How can that be if they're not OSPF-enabled?
When determining the Router ID (RID) of an OSPF-enabled router, OSPF will always use the numerically highest IP address on the router's loopback interfaces, regardless of whether that loopback is OSPF-enabled.
What if there is no loopback? OSPF will then use the numerically highest IP address of the physical interfaces, regardless of whether that interface is OSPF-enabled.
BOTTOM LINE: An interface does not have to be running OSPF to have its IP address used as the OSPF RID.
The OSPF RID can be changed, but it requires a restart or to reinitialize the OSPF routing process. Use the router-id command to change the default RID of each router as shown, and clear the OSPF process to do so.
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#router ospf 1
R1(config-router)#router-id 11.11.11.11
Reload or use "clear ip ospf process" command, for this to take effect
R1#clear ip ospf process
Reset ALL OSPF processes? [no]: yes
1d05h: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Serial0 from 2WAY to DOWN, Neighbor Down: Interface down or detached
1d05h: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial0 from 2WAY to DOWN, Neighbor Down: Interface down or detached
After entering the router-id command, the router console informed you that you have to reload the router or reset the OSPF processes for this to take effect. You enter the clear ip ospf process command to do this. Notice that when you're asked if you really want to do this, the prompt is ?no?? That's because all the OSPF adjacencies on this router will be lost and will have to begin the process again. That's OK on a practice rack, not good in a production network. Don't use that one at work.
The OSPF RID is not a complicated concept, but the fact that an interface doesn't have to be OSPF-enabled in order to have its IP address act as the RID takes some getting used to. And remember - when the router or switch asks you a question and the prompted answer is "no", take one step back and make sure you really want to do what you're about to do!
Dialer Watch allows you to configure a route or routes as "watched" when the watched route leaves the routing table and there is no other valid route to that specific destination, the ISDN link will come up. In the following example, R1 and R2 are connected by both a Frame Relay cloud over the 172.12.123.0 /24 network and an ISDN cloud using the 172.12.12.0 /24 network. The routers are running OSPF over the Frame cloud, and R1 is advertising its loopback of 1.1.1.1/32 as well as an Ethernet segment, 10.1.1.0/24, via OSPF. R2 has both of these routes in its OSPF table, as shown below.
R2#show ip route ospf
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/65] via 172.12.123.1, 00:00:07, Serial0
10.0.0.0/24 is subnetted, 1 subnets
O 10.1.1.0 [110/128] via 172.12.123.1, 00:00:08, Serial0
We want R2 to place a call to R1 if either the loopback or Ethernet networks leave R2's routing table, but we don't want to have to depend on interesting traffic. That dictates the use of Dialer Watch.
First, configure the list of watched routes with dialer watch-list. Only one of the watched routes needs to leave the routing table for the ISDN link to come up. In this example, R2 will watch both routes from its OSPF routing table.
Be careful with this command. The entries here need to match exactly the routes and masks being watched. Dialer watch-lists use subnet masks, not wildcard masks.
R2(config)#dialer watch-list 5 ip 10.1.1.0 255.255.255.0
R2(config)#dialer watch-list 5 ip 1.1.1.1 255.255.255.255
Configure the dialer watch-group command on the BRI interface, AND frame map statements for the watched routes. As with dialer-list and dialer-group, the group number referenced in the dialer watch-group command must match the number assigned to the dialer watch-list.
The Dialer Watch configuration will not work without frame map statements for each watched route. I repeat this because this is the step a lot of people leave out.
R2(config)#interface bri0
R2(config-if)#dialer watch-group 5
R2(config-if)# dialer map ip 1.1.1.1 255.255.255.255. name R1 5557777 broadcast
R2(config-if)# dialer map ip 10.1.1.0 255.255.255.0 name R1 5557777 broadcast
To test Dialer Watch, the Serial0 interface on R2 will be shut down. Since we're running OSPF, the route table will be updated almost immediately and the ISDN link should come up right after that.
R2(config)#int s0
R2(config-if)#shut
01:12:47: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial0 from FULL to DOWN, N eighbor Down: Interface down or detached
01:12:47: %LINK-3-UPDOWN: Interface BRI0:1, changed state to up
01:12:48: %SYS-5-CONFIG_I: Configured from console by console
01:12:48: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0:1, changed state to up
01:12:49: %LINK-5-CHANGED: Interface Serial0, changed state to administratively down
01:12:50: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0, changed state to down
01:12:53: %ISDN-6-CONNECT: Interface BRI0:1 is now connected to 5557777 R1
Within five seconds, the ISDN link is up. show dialer verifies that Dialer Watch is the reason the line was brought up.
R2#show dialer
BRI0 - dialer type = ISDN
Dial String Successes Failures Last DNIS Last status
5557777 2 0 00:00:11 successful
0 incoming call(s) have been screened.
0 incoming call(s) rejected for callback.
BRI0:1 - dialer type = ISDN
Idle timer (120 secs), Fast idle timer (20 secs)
Wait for carrier (30 secs), Re-enable (15 secs)
Dialer state is data link layer up
Dial reason: Dialing on watched route loss
Time until disconnect 108 secs
Connected to 5557777 (R1) A final note regarding Dialer Watch ... it will not work with RIP, but will with all our other dynamic IGPs (IGRP, EIGRP, OSPF).
Chris Bryant has sinced written about articles on various topics from CISCO CCNA, Personal Desktop and Cisco CCNP. Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage , home of free and CCNP tutorials! Pass the. Chris Bryant's top article generates over 27100 views. to your Favourites.