One reason the routing protocol terminology is confusing is that different
groups of engineers at Cisco implement the protocols, and they use
terminology in inconsistent ways. We've had a few questions lately about
how to learn Cisco concepts logically. Sometimes you just can't apply
logic! &;-)
EIGRP doesn't run between autonomous systems since it's an interior routing
protocol. I think it's a misnomer that the parameter used to identify an
EIGRP group of networks is called an autonomous system number, (although it
is sometimes recommended that one use an actual autonomous system number,
simply for documentation reasons.) It's also a misnomer to call the
parameter a process ID, although I've seen it called that also. It has more
significance than simply an identifier for software running on a single
router. The number must be the same for all EIGRP routers in an
internetwork that share information.
OSPF is an exterior routing protocol, so it has a need to identify a group
of routers in one domain, under one administrative control. These routers
are identified with an autonomous system number. OSPF also has the concept
of an area, which is a subset of neighbor routers within a domain. Routers
in an area share identical, detailed information about each other's links,
but have only summarized information about links outside their area.
The OSPF process ID simply identifies the instance of the OSPF software
running on a single router. It's like a UNIX process ID. It's just a local
housekeeping variable. It has no significance outside the router on which
it is configured, unlike the area and autonomous system numbers for OSPF
(and EIGRP) which have non-local significance. An interesting feature with
Cisco's OSPF implementation is that you can run OSPF multiple times on a
single router by using a different process ID for each instance.
Hope that makes some sense. Howard has written some good responses about
autonomous systems (which he says is not supposed to be abbreviated as ASS,
by the way &;-). Check the archives.
Priscilla
At 08:13 AM 12/27/00, [EMAIL PROTECTED] wrote:
>Hi folks,
>
>Can you help
>I 'm curently preparing for the BSCN exam which I hope to take end Jan
>beginning Feb. But I seem to be confused on some terminology on OSPF
>configuration. Consider the following line router ospf 1
>I know 1 is the proccess ID. The problem is how does this differ from the AS
>or area ?
>In contrast, in the following command router eigrp 200. 200 is the AS
>Is there a reason for this?
>I'll appreciate any help.
>Peace
>
>
>
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