Could someone please explain to me why some OSPF summary routes are more expensive than other routes (even if the cheaper route is accessed via the more expensive route)?
To illustrate my point, picture the following scenario: RouterA is connected to RouterB via network 1. Network 1 has a cost of 1. RouterB is connected to RouterC via network 2. Network 2 has a cost of 4. RouterC is connected to RouterD via network3. Network 3 has a cost of 16. Network 4 (which has a cost of 64) is only connected to RouterD. Network 1 is in OSPF area 1 (RouterA is an internal router and RouterB is the ABR for area 1) Network 2 is the only network in backbone area (area 0). Network 3 and network 4 is in area 2 (RouterD is an internal router and RouterC is the ABR for area 2) If you now perform a "show ip route" on RouterA, the cost to network 3 is 149 and the cost to network 4 is 85 !!! Even though network 4 is accessed via network 3, it is less expensive than network 3. The only rational explanation that I can find for this is that the ABR for Area2 adds an extra cost-factor for network 3 when it advertised it to other areas (but I cannot figure out why???). And if this is the case, why does it not add on an extra cost-factor for network 4 as well??? If someone had an answer to this, please enlighten me. I have to explain the OSPF costing concepts to some students (and how do you explain things if you do not understand it yourself?). Thanking you for your support on this forum. Abraham de Villiers (Diffy) Teltraswitch Facilitator Telkom Centre for Learning Tel : (021) 550 1855 or (021) 550 1800 Fax: (021) 551 4193 Cell: 082 824 9724 eMail : devilla1@telkom. Please Note: The information contained in this message may be confidential and is intended to be exclusively for the addressee. Should you receive this message unintentionally, please do not use the contents herein and notify the sender by return e-mail. This document could contain proprietary information. The dissemination, copying, disclosure, use or the taking of any action in reliance on the contents thereof without the written consent of Telkom SA Ltd is strictly prohibited. [GroupStudy.com removed an attachment of type text/x-vcard] Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=29876&t=29876 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
