Conditional Route advertising?

[trilerian1]

Hello,

I would like a specific subnet to see a route in the routing table where other subnets are not able to see it.  For example, let's say I want 10.1.1.0/24 to be able to route to 192.168.1.0 255.255.255.0 via next hop 1, but all other networks use the default route to a different router.  The reason I need to do this is because this is between 2 sites that have ip conflicts that I need to clean up.  Between the 2 sites is an ipsec tunnel that some networks use.  I have a new dark fiber connection to this site though and I want specific networks to be able to access through the fiber without hindering the ipsec tunnel.  Eventually the ipsec tunnel will go away and everything will go over the fiber, but not until I get the ip conflicts resolved.  

Thanks

[MHM Cisco World]

https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/16137-cond-adv.html

This will help you

[trilerian1]

Thanks, I wasn't sure if what I wanted to accomplish could be done with BGP.  It will be something I look into for the future. 

[MHM Cisco World]

Conditional Route advertising? <<- this what make me confuse, 
anyway check @paul driver solution. 

[paul driver · Accepted solution]

Hello

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@trilerian1 wrote:
 For example, let's say I want 10.1.1.0/24 to be able to route to 192.168.1.0 255.255.255.0 via next hop 1, but all other networks use the default route to a different router.  

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Policy Based Routing (PBR) would be applicable to do this, which when applied on a routers interface that the source traffic originates from would policy route that certain source based traffic via a different next hop other than the specific/default next-hop specified in the Global Route Table (GRT)

In the below example the next-hop address is considered reachable if the tracked object is up in that case the specified traffic stated in the access-list will be policy routed via the specified next-hop in the route-map, if the tracked object is not reachable that same traffic will be routed via the GRT specific or default route

Example:
ip sla 1
icmp-echo x.x.x.x ( tracked destination)
fre 5
ip sla schedule 1 life forever start-time now
track 10 sla 1 reachability

access-list 100 permit 10.1.1.0 0.0.0.255 192.168.1.0 0.0.0.255
route-map PBR
match ip adddress 100
set ip next-hop verify-availability x.x.x.x track 1 10

interface x/x
ip policy route-map PBR

[trilerian1]

This seems like a pretty easy solution.  I assume the route needs to be in the table for this to work and other networks will not use it based on the ACL.

Thanks, I'll update as the solution once I get it applied.  May take a bit, lots of projects...  

[trilerian1]

I was able to get this done today.  I used an extended ACL because this was only for specific networks to specific network.  I didn't use the sla.  So far so good.

Thanks

[MHM Cisco World]

@paul driver mention use IP SLA because if for some reason the next-hop is unreachable the traffic will drop to blackhole, so we need IP SLA to check next-hop when it not reachable the SW/R will use default RIB. 
it depend on you friend. 

[trilerian1]

For these networks if the traffic can't hit that next hop IP, it is destined to nowhere anyway.  But I will remember the SLA for a later time.

Thanks