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How to alter the route in an OSPF network

Posted: Thu Dec 16, 2010 6:43 pm
by psycoclan1
Ok guys, here's the problem i have.
I am a member of a metropolitan wireless network in greece and i have 2 backbone links. I want to reach a specific destination which can be reached in 2 ways. The problem is that the route 1 (cost 45) is somehow the "default" route but a link between me and the destination is problematic (high ping, low bw, often timeouts). The 2nd route (cost 35) is great (low ping, high bw). The OSPF is set to route my data from the 1st link but it causes me timeouts. Whenever i disable the 1st link, the data flow great from the 2nd one. I cannot add a static route because i cause conflict between the 2 links. So how can i solve this problem? I want to route from the 2nd link staticly!

Re: How to alter the route in an OSPF network

Posted: Thu Dec 16, 2010 6:55 pm
by fewi
The best thing to do would be to change the cost of the interface the undesirable link goes through. Make that cost very high. At that point the other link will be preferred, but you can still fall back to the worse link when the primary fails.

Re: How to alter the route in an OSPF network

Posted: Sat Dec 18, 2010 6:05 pm
by psycoclan1
The best thing to do would be to change the cost of the interface the undesirable link goes through. Make that cost very high. At that point the other link will be preferred, but you can still fall back to the worse link when the primary fails.

Undesireable link's cost is higher than the other's but still data are sent from there. No idea, i think i have to wait till they fix their APs :) thx anyways!

Re: How to alter the route in an OSPF network

Posted: Sat Dec 18, 2010 6:16 pm
by fewi
Look at the OSPF routing table - what is the cost of the two routes? The undesirable route will still have a lower cost than the one you want.
I should have been more explicit originally: look at the costs and increase the interface cost of the undesirable route by so much that the entire route's cost is higher than the one of the link you want. Route cost is cumulative over the entire path, just like the name of the routing protocol indicates.
You will of course also have the other side adjust their costs for return traffic so you don't have asymmetric routing.
You may find this entire wiki page helpful, though I am linking to the section that is specific to your question: http://wiki.mikrotik.com/wiki/Manual:OS ... alculation

Re: How to alter the route in an OSPF network

Posted: Sat Dec 18, 2010 7:50 pm
by psycoclan1
Look at the OSPF routing table - what is the cost of the two routes? The undesirable route will still have a lower cost than the one you want.
I should have been more explicit originally: look at the costs and increase the interface cost of the undesirable route by so much that the entire route's cost is higher than the one of the link you want. Route cost is cumulative over the entire path, just like the name of the routing protocol indicates.
You will of course also have the other side adjust their costs for return traffic so you don't have asymmetric routing.
You may find this entire wiki page helpful, though I am linking to the section that is specific to your question: http://wiki.mikrotik.com/wiki/Manual:OS ... alculation

oh i understand. No cost in the undesirable link was 45 (both sides) and changed to 70 (both) by me. But you say "whole route's cost must be bigger than the other's cost" right? So typing a cost for example 200 will make the undesirable link not preffered!

Re: How to alter the route in an OSPF network

Posted: Sat Dec 18, 2010 8:06 pm
by psycoclan1
Look at the OSPF routing table - what is the cost of the two routes? The undesirable route will still have a lower cost than the one you want.
I should have been more explicit originally: look at the costs and increase the interface cost of the undesirable route by so much that the entire route's cost is higher than the one of the link you want. Route cost is cumulative over the entire path, just like the name of the routing protocol indicates.
You will of course also have the other side adjust their costs for return traffic so you don't have asymmetric routing.
You may find this entire wiki page helpful, though I am linking to the section that is specific to your question: http://wiki.mikrotik.com/wiki/Manual:OS ... alculation

oh i understand. No cost in the undesirable link was 45 (both sides) and changed to 70 (both) by me. But you say "whole route's cost must be bigger than the other's cost" right? So typing a cost for example 200 will make the undesirable link not preffered!
cheers mate! i fixed it!