QUICK OSPF QUESTION...

I am trying to verify my simple OSPF configuration on the Boson Sim. and I have a question about the Router ID (RID). While viewing the "show ip ospf" command, I noticed that the router ID for one of my routers was the highest IP in the area. Lammle says the RID should be the highest IP on the router's loopback interface and if no loopback is configured then it is the highest IP of all active interfaces. Does that mean all active interfaces in the area or on the physical router's interfaces? Notice the RID is a OSPF learned subnet and not directly connected. Here is the output:

lab_A#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route

Gateway of last resort is not set

C 192.168.10.0 is directly connected, FastEthernet0/0
C 192.168.20.0 is directly connected, Serial0
O 192.168.30.0 [110/65] via 192.168.20.2, 00:00:28, Serial0
O 192.168.40.0 [110/65] via 192.168.20.2, 00:00:31, Serial0
O 192.168.50.0 [110/193] via 192.168.20.2, 00:00:18, Serial0

lab_A#show ip ospf
Routing Process "ospf 112" with ID 192.168.50.1 Supports only single TOS(TOS0) routes
SPF schedule delay 5 secs, Hold time between two SPFs 10 secs
Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs
Number of external LSA 0. Checksum Sum 0x0
Number of DCbitless external LSA 0
Number of DoNotAge external LSA 0
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
area BACKBONE(0)
Number of interfaces in this area is 2
Area has no authentication
SPF algorithm executed 4 times
Area ranges are
Number of LSA 4. Checksum Sum 0x2212D
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0

Lab_A#show ip ospf data

OSPF Router with ID (192.168.20.1) (Process ID 112)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count
192.168.20.2 192.168.20.2 1418 0x80000003 0x9084 1

Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum
192.168.20.2 192.168.20.2 1418 0x80000003 0x9084

But here it says the RID is 20.1 I can just see it now, a question on the test asking "How is the RID defined in OSPF?" Is the SIM buggy or is there more to it than what Lammle defines? Maybe the 50.1 in the show ip ospf output is the ID for the running process and not the Router ID?

Clarification would be appreciated. Thanks

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Comments

NightShade1

Look the router ID is defined this way

All ospf routers have their Router IDs
Now you can set them the router id by issuing router-id <ip address> in the OSPF process
OR
if you dont have any set for the router the router itseft will pick his router ID
How?
Well he will look for the highest ip address of any loopback interface configured on THAT router and pick it as router ID... if he doent have any loopback then he will pick the highest physical interface address to be his router ID

When a router pick his router ID he just look between his interfaces... he doestn look interface of other routers O_o

Anyways stop using BosonBugSim use Dynamips... or buy the real thing...

Does this answer your question ?

Netstudent

Well I kinda knew that already because thats what Lammle said in sybex. But I was just wanting to make sure because I got a different output for my RID than Lammle did for the "Sho ip ospf" command and I set up the lab in Boson exactly like he did in Sybex. But I know what the definition is so if I get asked on the test about it I'll use the definition. If its a scenario based question I'll use the "Show ip ospf database" and in the real world I'll manually configure it like you just showed me.

YA I know what you mean, I call it Bugson Simulator sometimes. I have been looking for some gear a lot lately with much interest. I have the money to get some nice equipment, I just haven't committed to dropping 800 or 900 bucks yet. I want something that will be adequate for CCNP as well.

NightShade1

just get dynamips.....

techman-aka-Format

remember the highest RID is the highest ip on the router of "active" loopbacks, or loopbacks that are up and up.
then if that is tied it looks to highest "active" interfaces.

if the interfaces are administratively shutdown,or down and down, they will not be considered in the RID process.

each RID is unique to each router.

Netstudent

Cool, Thanks guys...

NightShade1

DarbyWeaver wrote:

I love the command:

router ospf 1
router-id 150.150.150.150

Nice to make it a static value and damn the highest ip or highest loopback.

We call this nailing it down.

Lol thanks Darby was about to say that.. guess he didnt pay attention to what i have explained above tho....in which i mention that part

Netstudent

Netstudent wrote:

Well I kinda knew that already because thats what Lammle said in sybex. But I was just wanting to make sure because I got a different output for my RID than Lammle did for the "Sho ip ospf" command and I set up the lab in Boson exactly like he did in Sybex. But I know what the definition is so if I get asked on the test about it I'll use the definition. If its a scenario based question I'll use the "Show ip ospf database" and in the real world I'll manually configure it like you just showed me.

YA I know what you mean, I call it Bugson Simulator sometimes. I have been looking for some gear a lot lately with much interest. I have the money to get some nice equipment, I just haven't committed to dropping 800 or 900 bucks yet. I want something that will be adequate for CCNP as well.

Actually nightshade I pay very good attention. If you notice the last sentence in this paragraph where I said "in the real world I will manually configure it like you showed me". Maybe you should read the threads a little better before you assume someone isn't paying attention to what others have to say.

NightShade1

I wasnt even talking to you.... i was talking to techman-aka-Format
because he said

remember the highest RID is the highest ip on the router of "active" loopbacks, or loopbacks that are up and up.

This is not always like that... for example if i set the router ID instead letting the router picking it then the highest ip address of the loopback and blah blah blah will be not the router ID
Likei said before i could have a loopback address of 192.168.1.1 but if iset the router ID of 2.2.2.2 the router ID will be 2.2.2.2 and not the highest ip address of the logicals interfaces of that router....

You should put more attention to who the ppl are refering to :P

Netstudent

oh sorry it looked like you were referring to me..