Floating Static into BGP for ISDN Backup

[eunsonrd]

Hi , I have a network with a private BGP AS per site , through Carrier mpls BGP Cloud. I have a requirement to set up ISDN Backup from one of these sites to a few others.In the event of the MPLS going down this ISDN interface should be raised to the remote site that is down.  I plan to use dialer interface per ISDN remote site and static route ( floating admin distance 200 ) to that site via the dialer interface.

I need to then advertise that on eBGP to other sites.

Now I am wondering if the MPLS sites are normally up and running , then the floating static will not be in the routing table , therfor wont be redistributed into BGP by the redistribute static comand until the MPLS route is lost?

or

Would I need to use something like a  redistribute static routemap , then in the routemap add prepended AS to make sure the as path is longer for ISDN backup than it would be for existing MPLS normal route?

Or maybe there is a simpler way?

I probably only get one go at this so I need to be sure.

[Edison Ortiz]

Now I am wondering if the MPLS sites are normally up and running , then the floating static will not be in the routing table , therfor wont be redistributed into BGP by the redistribute static comand until the MPLS route is lost?

If the static prefix is in the BGP routing table, then it won't be redistributed into BGP as BGP has a better AD. If the static prefix isn't in the BGP routing table, then redistribution will occur.

Do a show ip route [ip address] and tell us what protocol that prefix is associated - BGP or static.

[meperuma]

Hi,

I would like to understand how you are planning to do this? I mean the ISDN setup? R u going to use ISDN dialout from remote site to the ISDN hub router router ( may be at your main site) . The reason I am asking is that do u consider interesting traffic I.e dialer on demand Or always on ISDN

My suggestion is choose igp routing protocol On the ISDN network and redistribute on ebgp. When the ISDN connection become active, routing protocol establish over ISDN and route redistributed from hub.this will be more dynamic

You still need to use a floating static on the remote side this floating static can be a summary.

A careful consideration of your setup to be taken into this. Poor design might cause unnecessary ISDN charges, routing loop due to backdoor

Also, you can explore the possibility of using object tracking if ip reachablity and use EEM to perform certain action I.e adding a static route

HTH

Sent from Cisco Technical Support iPhone App

[eunsonrd]

Ok so normally sites are available via MPLS ( and BGP)  so there will be routes available to that remote site normally , via eBGP.

In the event of a remote router MPLS failing I intended to have ISDN at central SITE1 and remote site SITEA going up. ( any one of 5 remote sites actually). When this is up other remote sites need to see this route ( via BGP ).

So the intention was to create Dialer inteface at both central SITE1 and remote sites SITEA. dialer list for interesting traffic ( to ensure not falsely put up as you say), and a floating static ( admin distance 240 etc).  So when the MPLS for any SITEA goes down,BGP route is removed for the remote SITEA,  a floating static will be installed in the routing table , dialer list applied , and the dialer interface will bring up the ISDN connection to the remote SITEA. At this point the central router SITE1 and the remote router SITEA will see each other via ISDN , I am happy with this to this point, fairly standard.

However I need this new ISDN route to also be available to other remote sites, which are still connected via Central router via eBGP. So suggestion is to redistribute static ( the floating static) into BGP.  So my question is if this floating static will be redistributed into BGP even when the MPLS BGP link to SITE A is up ? Obviously I dont want this I only want the route when real MPLS and BGP path are down. ( Im not sure if the floating static is added to BGP if there is already a BGP path in there?)

So if I do redistribute , and the floating static is in BGP even when Real MPLS/BGP route is available, then perhaps if I add a routemap to the static redistribution and append the BGP AS number many times , it can never be preferable if there is an alternative proper MPLS BGP Path.  

So in summary 2 questions , will the floating static be redistributed into BGP even when not active , in that event could I apply AS prepending via routemap to them to make less preferable?

Or some other simpler way?

Note this is a live network , I dont have a lab to work this out on, so need to do it on paper unfortunately.

[meperuma · Accepted solution]

Ok,   to answer your question "will the floating static be redistributed into BGP even when not active " , NO, only if static route is higher AD than eBGP / IGP. The reason is that RIB (routing Information base) will choose the lower AD as the best exit to reach a prefix. If the prefix is lost, then rib calculate the next  next available prefix and send update to the respective protocols (here eBGP)

HTH

[eunsonrd]

Thanks , that was my assumption, only redistribute if in the routing table. Good to check now rather than halfway through a change! Thanks for your help.