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dedicated links for specific prefix in ospf

[ Edited ]
‎02-09-2017 12:26 AM

juniper question.png

ospf is running in these devices,

want to make the red line for specifix prefix 3.3.3.0/24 and 4.4.4.4/0

 

is a way  to achieve this?

JNCIE-SP/JNCIP-SEC/CCNP
5 REPLIES 5
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Routing

Re: dedicated links for specific prefix in ospf

‎02-09-2017 08:36 AM

Hello,

 

You could configure static routes in s1, s2, s3 and s4 for 3.3.3.0/24 and 4.4.4.0/24 with the dedicated links as next-hops. You should not configure ospf in those links, and the static routes should be configured with no-readvertise. Also make sure that in case of a link failure the interfaces will go down, if not configure bfd for static routes. The subnets 3.3.3.0/24 and 4.4.4.0/24 should be redistributed into OSPF, so this way in case the dedicated links go down, you will still have reachability through the other links.

 

The reason for this proposal is because you cannot modify ospf routing behaviour inside an area. So there is no way to have ospf in that link and make it only advertise/accept a certain IP subnet. The protocol static preference is lower than ospf, hence the static route will be preferred, and in case the link fails, static route will be removed from the RIB and the ospf route will be used.

 

If you have any doubts please share them.

Regards.
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Re: dedicated links for specific prefix in ospf

‎02-11-2017 04:49 AM

If I understand this correctly you need two links instead of one for the router connections.

 

If so, you simplest solution is to create an AE interface. 

 

Add AE to the configuration

Move the ip address on the current link to the ae.0 interface

move the current physical link to be a member of teh ae.0 interface

add your new second physical link to the ae.0 interface

 

Now you have two physical links that behave as a single one.  And you can add more physical links as needed in the future.

http://www.juniper.net/documentation/en_US/junos/topics/task/configuration/link-aggregation-cli.html

Steve Puluka BSEET - Juniper Ambassador
IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP)
http://puluka.com/home
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Re: dedicated links for specific prefix in ospf

‎02-13-2017 05:21 PM

hello Steve

We don't want to use AE

 

any other suggestion for it?

JNCIE-SP/JNCIP-SEC/CCNP
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Re: dedicated links for specific prefix in ospf

‎02-14-2017 03:14 AM

As mentioned above, OSPF will not allow the behavior you want.  So you will need to change routing protocols for the links.

 

Besides the static routes mentioned above you could switch to BGP.  You would use local preference and your export policies to insure that the link you want to use as the primary path for prefixes is the preferred one on each side.

Steve Puluka BSEET - Juniper Ambassador
IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP)
http://puluka.com/home
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Re: dedicated links for specific prefix in ospf

‎02-16-2017 01:23 PM

Hello there,

 

One way to achieve this requirement is to run dedicated OSPF process over red links. JUNOS calls it "routing-instance type no-forwarding". If 3.3.3/24 and 4.4.4/24 are in default OSPF process, redistribute only those prefixes into that dedicated process.

Example config here http://www.juniper.net/documentation/en_US/junos12.3/topics/topic-map/ospf-routing-instances.html#jd...

Another way is to use OSPF multi-topology routing (MTR) with FBF

http://www.juniper.net/documentation/en_US/junos/topics/concept/multitopology-routing-overview.html

HTH

Thx
Alex

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