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Odd OSPF route selection

Tue Jul 15, 2014 12:52 am

Please see attached screenshot. This is of a router, say R2, which is sandwiched between 2 other MT routers , R1 & R3 directly connected to interfaces ether_1, and ether_6 on R2

ISP1 <- >R1< - > R2 < - >R3< - >ISP2.

Ospf is running across all 3 routers, R1, 2 & 3. BGP is running on R1 and R3 only.

What seems to be happening to R2 is that its preferred gateway is ether_6, which ip/routes correctly indicates. but traffic is almost symmetrical, which it should not be. It also seem to be receiving traffic from ether_1, which I have weighted higher to stop R2 from using this interface unless ether_6 goes down.

How would I go about diagnosing this problem?
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jkarras
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Re: Odd OSPF route selection

Tue Jul 15, 2014 6:15 am

You will need to know what type of traffic is coming in. Is it traffic to/from a directly connected route e.g. non ISP traffic?
 
CelticComms
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Re: Odd OSPF route selection

Tue Jul 15, 2014 7:05 am

What does the routing table look like on R2 and exactly what did you "weight"?
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Re: Odd OSPF route selection

Fri Jul 18, 2014 12:21 pm

What does the routing table look like on R2 and exactly what did you "weight"?
Here is a snipet of the routing table in R2. its gateway is 10.12.130.1 which is exactly where I want it to go...
I changed the weights or costs in routing/ospf/interfaces.
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Re: Odd OSPF route selection

Fri Jul 18, 2014 12:31 pm

Actually, now that I look at the routes again, everything seems to be destined for 10.12.129.1, which is R3. I do not want it to go out through this router, so I have increased the costs of the ospf interfaces on both R2 and R3 to stop this.

But yet at the top of the routes it says everything, 0.0.0.0/0 is destined for 10.12.130.1 which is R1
 
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Re: Odd OSPF route selection

Fri Jul 18, 2014 2:40 pm

Check the settings for default route redistribution from both your WAN routers including the cost for the default route. From your screenshot the router attached to Ether 6 is offering a more attractive default route than the other router while the explicit routes offered by the router on Ether 1 are being favoured.
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Re: Odd OSPF route selection

Sat Jul 19, 2014 12:01 am

Check the settings for default route redistribution from both your WAN routers including the cost for the default route. From your screenshot the router attached to Ether 6 is offering a more attractive default route than the other router while the explicit routes offered by the router on Ether 1 are being favoured.
On both WAN routers, Redistribute Default Route if installed (as type 1) is selected.
Default Route Metric is 1 on both routers.
 
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Re: Odd OSPF route selection

Sat Jul 19, 2014 12:12 pm

On both my BGP routers, should I have any of the Redistributes ticked under BGP/INSTANCES?
I had Redistribute Ospf ticked, but I removed it and now none of the redistributes are ticked, but the internet is still working.

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