topic Re: Select route with shorther prefix length in General Topics

Select route with shorther prefix length

COM-UCO — Wed, 08 Feb 2017 18:00:28 GMT

I have a static route for 172.16.0.0/12 but my PA is also learning through OSPF a route for 172.16.0.0/24.

As these routes have different prefix length both are installed in the routing table and the dynamic route for 172.16.0.0/24 learnt through OSFP takes precedence over static route for 172.16.0.0/12 without having in consideration the administrative distance.

I would like to avoid this situation and force my PA to select the static route with a shorter prefix length. Any suggestion?.

Thanks in advance!!!

Re: Select route with shorther prefix length

pulukas — Wed, 08 Feb 2017 23:06:27 GMT

More specific routes will always win over larger prefixes. This is the nature of the route selection process and is considered before the protocol of the route in question.

You will need to install the /24 as a static to override the OSPF learned route.

Re: Select route with shorther prefix length

COM-UCO — Thu, 09 Feb 2017 08:37:51 GMT

Steve, thank you for your answer. The problem is that my PA is learning a lot of routes with larger prefixes. So I would have to install a lot of static routes to solve the problem with the workarround that you suggest. Moreover, I would have to keep an eye on for new routes learnt by OSPF and install new static routes.

The ideal solution would be to filter the routes learnt by OSPF but, as far as I know, PA doesn't support this feature. I opened another thread about this:

https://live.paloaltonetworks.com/t5/General-Topics/How-to-ignore-routes-learned-by-OSPF/m-p/139314

Re: Select route with shorther prefix length

pulukas — Sun, 12 Feb 2017 14:01:55 GMT

Right, if you need that level of route filtering you will need to switch to BGP from OSPF.

Bear in mind that Palo Alto is a security company that provides networking features on their devices. The introduction pace of new networking features can be slow. We just got BFD for example last year. So don't count on networking feature requests showing up soon.