Got it! Because of my lack of experience with OSPF, the original
question confused me until I thought through the configuration. Until
then, I still thought of routers or interfaces belonging to areas. What
really helped me to conceptualize this issue was to toss out that idea
and think of only *links* as belonging to areas.
Put into context, I realized that given the original situation, the
link between the two routers would either be in area 0 or in area 1
depending on the configuration. I know, most people probably already
understood that, but for some reason I just hadn't thought of it that
way before.
Thanks for the clarification,
John
>>> "Howard C. Berkowitz" <[EMAIL PROTECTED]> 2/28/01 3:01:58 PM >>>
I haven't seen any of my posts show up for about a day or two -- not
sure they are getting through. Feel free to post this since yours,
clearly are! I'll copy to groupstudy just in case my posts start to
work.
>I think I must be missing something here, or I don't understand the
>concept of ABR.
>
>If you have a 7513 in area 0 connected to a 4500 in area 1, for
>instance, then the 4500 will have one interface in area0 and the rest
>presumably in area 1. By definition, that makes the 4500 an ABR,
>doesn't it?
Yes.
>I don't see how you have any choice in this matter at all,
>but since I've never actually configured OSPF perhaps someone will
>enlighten me.
In the situation described, the choice -- which I often like to do --
is not to put any area interfaces on the 4500.
Assume the 4500 is in area 0.0.0.1, and the WAN link to the core is
192.168.0.0/30. There's another 4500 in area 0.0.0.2, with a WAN
link, 192.168.1.0/30.
Then, a configuration snippet for the 7513 might be:
int s0.1
ip addr 192.168.0.1 255.255.255.252
int s0.2
ip addr 192.168.1.1 255.255.255.252
int fe0
ip addr 172.16.0.1 255.255.255.0
router ospf 1
network 192.168.0.1 0.0.0.0 area 0.0.0.1
network 192.168.1.1 0.0.0.0 area 0.0.0.2
network 172.16.0.1 0.0.0.0 area 0.0.0.0
In this example, I deliberately put area 0.0.0.0 on a Fast Ethernet.
Often, I keep 0.0.0.0 very small. If I have redundant core routers,
I'll connect them to switch ports on a common subnet. I'll usually
connect infrastructure servers such as SNMP, DNS, and DHCP to that
subnet, but I avoid putting any application servers into it.
Even if the core routers are colocated at the same site as the
application servers, I'm quite prone to put the servers in their own
area. One of the advantages of doing so is keeping server-to-server
traffic, such as synchronization and backup, out of the core.
>
>>>> "Hennen, David" <[EMAIL PROTECTED]> 2/28/01 9:32:59 AM >>>
>Hi, I am preparing to bring up a new site in an ospf network. The
new
>site
>will be a training facility connected back to the main office by a
t1.
>Currently we use OSPF and have everything in area 0, around 100
>routers.
>
>I want to make this new site a different area and to make the new
area
>a
>Totally Stubby Area. We have two 7513 routers at the main office
that
>handle all the wan traffic, the new remote office would connect to
one
>of
>these. The remote training office will have a 4500.
>
>One of my coworkers suggested that the 7513 at the main office should
>be the
>Area Border Router, because we should keep area 0 from being spread
out
>over
>a bunch of wan links. I had it in mind that the remote 4500 should
be
>the
>ABR. I don't have a strong reason for thinking that way. The cpu of
>the
>7513 runs between 20-30 % utilization according to snmp info.
>
>Are there any rules of thumb regarding this? I looked through the
>Cisco
>OSPF network design book and can see some examples that support
having
>the
>ABR at the main office. Is that the accepted practice? Are there
any
>gotcha's to look out for?
>
>Thanks if you can help
>dave h
>
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