The best way to transition from our switched network to routed that I can figure is to set up the existing VLANs for our geographic areas as OSPF areas and start dividing off our existing tower sites with mikrotiks on-site. I've had a backbone area set up between our Riverstone (ASBR) and mikrotik routers (ABRs), and now I've created the additional areas for the three vlans.

The riverstone has the default route out of the network and is DR for backbone area 0 and is only a member of area 0, so it should be the ASBR. By my reckoning, the backbone mikrotiks should be ABRs (members of area 0 and 1, 2, 3), then the tower site mikrotiks will be members of 1, 2, OR 3.

But, they're all showing as ASBRs, and I'm not understanding why. They're all only running OSPF, and there is only one router (only in area 0) with a static default route out of the network. Any thoughts why I'm seeing this?

Here is a simple example of my OSPF configuration. In reality the IPs are different and there will be more routers in each zone, but first things first...:

Area 0 (broadcast), 10.0.0.0/27, riverstone-1 ASBR is 10.0.0.1 and mikrotik-1 ABR is 10.0.0.2
Area 1 (NBMA), 10.0.0.32/27, mikrotik-1 ABR is 10.0.0.33 and mikrotik-2 @ tower A is 10.0.0.34
Area 2 (NBMA), 10.0.0.64/27, mikrotik-1 ABR is 10.0.0.65 and mikrotik-3 @ tower B is 10.0.0.66
Area 3 (NBMA), 10.0.0.96/27, mikrotik-1 ABR is 10.0.0.97 and mikrotik-4 @ tower C is 10.0.0.98

Thanks!

-Paul

Do you perhaps have redistribute connected or static enabled? Any kind of redistribution into OSPF (perhaps even if it is just enabled but not actively redistributing any) will cause a router to be an ASBR.

I do have redistribution on. I need to have that since these routers are PPPoE servers, correct?

That sounds likely. As awsmith noted, all redistributing routers are per definition ASBR, since they, by OSPF's point of view route on the boundary of the OSPF Autonomous System.

Eising is exactly right. Are you just curious as to why your routers are showing up as ASBRs, or do you have a specific reason for not wanting them to be ASBRs?

If you have some need for them not to be ASBRs, and if you assign netblocks for pools for PPPoE customers per router, you could put a "catchall" address on a bridge interface (ie, 192.168.200.1/24 if you assign /32s out of 192.168.200.0/24 for your PPPoE links) with arp turned off , add it to your OSPF network and set the interface to passive, turn off redistribution, and, advertise, as a native OSPF network, the /24. Then, your routers would not become ASBRs and the /24s would be native OSPF routes that got packets to the router, where they would either direct traffic to the more specific /32s of connected PPPoE clients, or send an ICMP host unreachable (or silently drop, depending on your firewall settings) for the not-connected destination addresses.

If your question was more along the lines of "why are my routers becoming ASBRs", I hope this answered your question and assures you that it isn't a bad thing.