Default Static Route

[Sagar4]

How to determine which next hop interface should be used for configuring default static route on any router if it is connected to multiple routers at its various interfaces? Also, how to choose next hop for configuring static route for any destination route not directly connected to our router's interface?

[David Ruess · Accepted solution]

Hello,

You would probably choose the router that's the closest to getting the network out, being the default. Ideally you'd want a routing protocol to take care of this because it can switch over if one fails. So if the way out of the network is out G0/0 then you would configure the next hop the IP address of the neighbor router connected on that link.

If you wan to load balance you can configure 3 default static routes and since the have the same AD they will load balance.

For the route not directly connected just point it in the right direction. For example:

If the network 192.168.1.0/24 is through R5 but not directly connected to R5 you can just point it to R5. Then once it gets to R5 if it doesn't know then you need another static route to keep pointing it down the line until it gets into its destination. You would also need a route back in order to have traffic flow in both directions.

Hope that helps

-David

[Sagar4]

So that means, in the case of static routes, we should know the network topology so as to make sure we choose right next hop for a particular destination route unless we want to configure static routes across multiple interfaces.

And what about configuring default route, can we choose anyone next hop router's ip address in case we are connected to multiple routers?

[David Ruess · Accepted solution]

You can. However as you mentioned its ideal to know the network so you know where to configure routes, or as I mentioned have a dynamic routing protocol do it for you. If you point the default route to a next hop IP and that device fails then you would have to go in and configure another default route to another next hop.

Also when its next hop its the other sides interface IP connected to the local router. 

[Sagar4]

Thanks for clarifying my doubt. One more thing I would ask related to this is if there is any command we can use on our own router to determine the next hop router's interface ip address which we would use in case we don't have remote login access to that next hop router? Or de we have to figure that out manually via physical connection to that next hop router?

[David Ruess · Accepted solution]

You can try to do a

show cdp neighbor detail

if running CISCO gear and its turned on on the other side and yours. Or if the mask is 255.255.255.252 then there are only 2 IPs it can be and your local router will be one of them. So the remote router would be the other one.

If you can call who owns the device and ask them, that is another option too.

[Sagar4]

Thanks david.

@MHM Cisco World Using egress interface for configuration without next hop ip address is only for P2P link and not broadcast network. But thanks for advice.

[MHM Cisco World]

Yes it not recommend but

If you set next-hop and it down then your static route will not forward traffic

If you use egress then you can use any router relpy to your arp.

[Joseph W. Doherty]

As David notes, CDP (or LLDP), or if using a /30 or /31, might provide the other side's IP, but basically, as David mentioned earlier, we (should somehow) already know were we want certain prefixes to go for their next-hop.  This because we either are managing the whole network and/or we're working with other network operators that can tell us what our next-hop choice is for network prefixes they support.  (The latter case doesn't mean we need to know anything about their [other network's] internal topology, just for prefix 1.2.3.4/24, send the packets to this IP.)

If we're doing dynamic routing, we also need to know what routing protocol to use and the specific parameters to use to "converse" with another router (if not ours - if ours, hopefully, again assuming it's your network, you should have all the needed info).

[MHM Cisco World]

Multi router connect which is case of connect routers to SW you can use only egress interface without next-hop

Next-hop not direct connect, you can use next-hop with track. This scenario is so critical, if you not full know topolgy then blackhole can drop your packet.