>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.
Yep. There are several subtleties to this, until you really get an
emotional understanding of "link." The idea that a router link
(i.e., type 1 LSA) is different than a physical router, and that it
can involve such weirdnesses as being a router link in each area to
which the physical router (or the OSPF process) connects.
Warnings though: OSPF and ISIS look at things a little differently.
In OSPF, it is the interfaces of the single router that go into
different areas. In OSPF, it is more the concept of the physical
router being aware of its own area alone (i.e., type 1) or of other
areas and the backbone (type 2).
My new white paper on certificationzone.com, which should be up
tomorrow, compares link state protocols and scalable routing in
general. A set of OSPF and ISIS specific papers will follow.
>
>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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>>
>>
>>
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