http://www.cisco.com/univercd/cc/td...m#xtocid1794737

"Router# show ip ospf interface ethernet 0
(...)
AS 201, (...)
(...)

Table 54: show ip ospf interface Field Descriptions:
AS: AUTONOMOUS SYSTEM NUMBER (OSPF PROCESS ID), (...)"

QUESTION:
i didn't expect the OSPF PROCESS ID to be the AUTONOMOUS SYSTEM NUMBER.

assuming that the description for PROCESS ID is:
"INTERNALLY used identification parameter for an OSPF routing process. It is locally assigned and can be ANY positive integer. A unique value is assigned for each OSPF routing process"...

->at which level the concept of "AUTONOMOUS SYSTEM" does apply when using OSPF?

thanks for your comments
frans

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quote:

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Originally posted by emo francois:
QUESTION:
i didn't expect the OSPF PROCESS ID to be the AUTONOMOUS SYSTEM NUMBER.

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The "ospf process id" and "autonomous system number" are simply different names for a unique id among ospf processes on the same router. I don't know how clear the above statement is, so let me try a bit harder.

I enabled ospf on one of my routers with "router ospf 12". You would expect to see an ospf process with process is 12, right? Such is not the case. A "sh process cpu" shows TWO ospf processes: an "ospf hello" process with pid 73, and an "ospf router" process with pid 80. So 12 is not THE "ospf process id"; 12 happens to be a "Entity MIB API". So much for process id...

As for the AS number, assume you're the administrator of an autonomous system that is given a unique number by somebody (I don't know who, maybe InterNIC). Say that number is 111. You would assume you have to do "router ospf 111", but that's not true; you may use whatever number you want, it doesn't have to be 111. As it turns out, ospf routers don't exchange AS numbers (take a look at Hello packets, used to establish adjacencies; hmm, no "as_number" field). You may very well put three ospf routers in the same AS with "router ospf 1", "router ospf 2" and "router ospf 3", respectively (provided you configure them properly, so that they become neighbors).

Now, you know you may have multiple ospf processes running on the same router. You (and the IOS) need to be able to differentiate between them. That's where the "x" in "router ospf x" comes into play.

As an aside, global AS numbers DO make sense in BGP, where you need to construct the AS_PATH.

Hope this helps!


[This message has been edited by dmaftei (edited 12-22-2000).]

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quote:

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Originally posted by dmaftei:
As for the AS number, assume you're the administrator of an autonomous system that is given a unique number by somebody (I don't know who, maybe InterNIC.

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quote:

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Originally posted by MadChef:
In the States it would be the American Registry for Inernet Numbers at www.arin.net.

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Good to know. Bookmarked already. Thanks!

quote:

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It turns out that as soon as someone stops paying me to think (I'm on vacation right now) I stop thinking. Hah.
Others would argue that I stopped thinking long ago.

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Hmm, I wouldn't take it so hard. It's obvious you know your stuff, and something extra. So, you missed one -- big deal. You have the power to admit it, and the ability to learn from it, that's what's important. You earned the respect of everybody (well, almost...) here, and you absolutely deserve it. Maybe I should stop before I become pathetic...

Enjoy your vacation!

The Big Bad Wolf

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