"Is there a document explaining the rules of summarization when there are two ABRs on a area?"
I believe you would summarize the same, unless you had special needs. The cumulative cost from the ABR back to the source of the traffic should allow the routers in-between to choose the correct path. So if you had: Ra----Rc----Rd | | | | 5 | 0 | | | | Rb----Rd----Re Routers Rc and Rd would be the ABRs. In summarizing into the backbone, or summarizing out to area 5, you would setup the same summary ranges. Assuming all links were the same cost, Ra would go through Rc in order to get to anything in area 0 (assuming all networks were summarized) and Rb would go through Rd. Similarly, Rd would go through Rc in order to get to anything in area 5, while Re would go through Rd. Now, in the original question (unless I've gotten questions confused, which is definitely possible), there was no link between Ra and Rb (and there never was). So, although they were both "called" area 5, they were in fact two different areas. Ra and Rb never shared the same database (assuming that the link between Rc and Rd was in area 0) at any point in time. If they summarized their whole "area" (including routes off of both Ra and Rb in the misguided thinking that both area 5's were the same area), then Rd would send traffic destined for Rb to Rc, which wouldn't have a more specific route for it. Re would send traffic for Ra towards Rd, which also wouldn't have a more specific route for that traffic. As long as you have your areas properly connected, you shouldn't have to worry about any special summarization requirements, other than if you want traffic to flow a particular way due to bandwidth, cost of service, or some other external consideration. Fred Reimer - CCNA Eclipsys Corporation, 200 Ashford Center North, Atlanta, GA 30338 Phone: 404-847-5177 Cell: 770-490-3071 Pager: 888-260-2050 NOTICE; This email contains confidential or proprietary information which may be legally privileged. It is intended only for the named recipient(s). If an addressing or transmission error has misdirected the email, please notify the author by replying to this message. If you are not the named recipient, you are not authorized to use, disclose, distribute, copy, print or rely on this email, and should immediately delete it from your computer. -----Original Message----- From: alaerte Vidali [mailto:[EMAIL PROTECTED] Sent: Monday, July 21, 2003 3:06 PM To: [EMAIL PROTECTED] Subject: RE: Two ABRs on the same area - requirements [7:72587] Thanks, The challenge I am facing is to improve the OSPF design of a network that is in production, without changing the existing WAN links. The area 5 is bigger than I think it would be ideal (there are 56 routers) and there is no interesting traffic between all the spoke routers in the area, as Howard mentioned. In the beginning I were wondering about transforming R1 in an ABR; but I gave up because the stability of the backbone (R1 is not so powerful as the others, R2 and R3). Also, today there are two ABRs in area 5, and it would have just 1 ABR with this change. Now I am considering to change the spoke routers connected to R3 to a new area. Today there is only one exit point for the spoke routers connected to R3, and it would not be changed. R3 would be connected to R2 (through area 0 and area 5) and to R1 (through area 5), as it is today. R2 and R3 would be the ABR for area 5; no changes here. R1 has an ATM link to its two ABRs, R2 and R3. The main link is to R2; the link to R3 is a backup. R3 would participate in area 5 just because the existing WAN link to R1. R3 would be the ABR for the new area, probably area 6. The benefit is a small database for area 5 and area 6, without flooding information where it is not useful. Is there a document explaining the rules of summarization when there are two ABRs on a area? Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=72719&t=72587 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
