Network Traffic from one end to another with static routes configured

[kennethsali]

Hi there,

I have got a query in regards to two routers that are configured with EIGRP across the Frame Relay network.

Router A is configured as follows:

LAN: 192.168.100.1 /29

WAN Sub-interface: 10.220.18.37 /30

Router B is configured as follows:

LAN: 10.240.86.253 /29

WAN Sub-interface: 10.220.18.38 /30

Both Routers are directly connected via the serial connection over Frame Relay.

In Router A's routing table there is a route to the network 10.240.86.248 /29 (at the back of Router B)known via eigrp.

On that same network is a couple of other routers with addresses 10.240.86.253 & 251.

However, there are static routes on both routers as follows:

ip route 10.10.16.0 255.255.255.0 10.240.86.253

ip route 10.55.0.0 255.255.0.0 10.240.86.253

Both networks 10.10.16.0 & 10.55.0.0 are at the back of Router B's LAN somewhere and can be accessed from Router A through Router B.

Now the next hop stated is presumably invalid on Router Aas 10.240.86.253 is not an address on any of the directly connected devices, however a traceroute from these networks works perfectly OK.

Does the router discard the static route and use EIGRP or does it then look for the next hop netowrk in its routing table and uses it because this router will not bring up an error command stating that the next hop is invlaid.

Please help out as I am totally confused.

Many Thanks

Ken

[Richard Burts]

Ken

Your question is based on an assumption:

Now the next hop stated is presumably invalid on Router Aas 10.240.86.253 is not an address on any of the directly connected devices,

But your assumption is flawed. It is not required that the next hop of the static route be directly connected, it is only required that the next hop be reachable via something known in the routing table. This is known as recursive routing lookup. So router A has the static routes with next hop 10.240.86.253 and router A looks in its routing table and asks can I get to that address? And the answer is that router A does have an entry in its routing table that the address is reachable via 10.220.18.38, so router A will happily (and successfully) forward traffic using those static routes.

HTH

Rick