Redistributing static routes into OSPF and applying path costs

[BruteForce]

Hey there,

I have situation where I need to redistribute static routes into OSPF and apply a cost to prefer one path over another, but I don't really know how admin distance of a static route being

redistributed

is going to affect OSPF. 

My situation is this. Lets say I have a computer with an IP of 192.168.10.1. This computer connects to an AN which then is trunked over to a DN that hosts that subnet. That DN has an uplink to CN1 and CN2 for redundancy. CN1 has an uplink to a boundary type device that has an IP of 192.168.5.5 /28. CN2 goes up to a different boundary type device, and that device's IP is 192.168.5.20 /28. 

192.168.10.1 (the computer) can go through either CN1 or CN2 to hit the boundary. The two CNs advertise OSPF routes to each other. I would like to put a static route on CN1 that send traffic from 192.168.10.1 to 192.168.5.5. This static route needs to be

redistributed

into OSPF as the primary route. CN2 will send the computer to 192.168.5.20 if 192.168.5.5 is detected as down. How can I configure this?

CN1:

router ospf 1

redistribute static metric-type 1 subnets

(I'm unsure if this command is applied correctly)

ip route

192.168.10.1 255.255.255.255 192.168.5.5 (I'm unsure what to put for distance metric here)

CN2:

router ospf 1

redistribute static metric-type 1 subnets 

(I'm unsure if this command is applied correctly)

ip route 

192.168.10.1 255.255.255.255 192.168.5.20 (I'm unsure what to put for distance metric here)

-----

Any help would be appreciated. 

[David Ruess · Accepted solution]

Hello,

When

redistributing

routes the metric is taken over by the

redistributed

protocol. So if you put a metric or AD on a

static route

its overwritten during

 redistribution

to the protocols metric. For OSPF this is a metric type-2 (E2) and a cost of 20. You can influence this with a

route map

and

prefix-list 

or within the

 redistribution 

statement itself.

You can accomplish this a couple ways. 

1. Leave the matric type as Type-2 for both routes and adjust the cost during

redistribution

to prefer CN1. (this is the example demonstrated below)

2. Configure CN1 route as type-1 when being

redistributed 

and leave CN2

static route

as the

default Type-2 route

. OSPF chooses Type-1 over Type-2 routes.

CN1:

router ospf 1
redistribute static subnets metric <lower number than CN2>

ip route 192.168.10.1 255.255.255.255 192.168.5.5 (I'm unsure what to put for distance metric here)



CN2:

router ospf 1
redistribute static subnets metric <higher number than CN1>

ip route 192.168.10.1 255.255.255.255 192.168.5.20 (I'm unsure what to put for distance metric here)

*Note: if you have multiple

static routes

and you only want those specific ones

redistributed

in you will need to create a

prefix list 

identifying them and applying it to a

route-map

. Then you can configure the

route-map

as part of the

redistribution 

like the example below:

redistribute static subnets route-map OSPF metric

<#>

Make sure the

route-map

references the

static routes

you want to

redistribute.

Hope that helps

-David

[BruteForce]

Thank you. I'm looking into

 ip prefix-lists

and

route-maps

now.