Lab Objective
Configure static routes on two routers using the outgoing interface syntax rather than specifying a next-hop IP address, and verify traffic routes correctly across a point-to-point serial link.
Lab Purpose
Static routes, discussed earlier in this series, can be configured pointing to either a next-hop IP address or an outgoing interface. The interface-based syntax works cleanly on point-to-point links but should generally be avoided on multi-access networks, a distinction this lab makes concrete.
Lab Topology
R1 ---- Serial0/0/0 ------ Serial0/0/0 ---- R2
R1: 10.20.20.1/30, LAN 192.168.10.0/24 (Loopback1)
R2: 10.20.20.2/30, LAN 192.168.20.0/24 (Loopback1)Task 1: Configure Basic Addressing
Configure the serial interfaces and a loopback on each router representing its local LAN.
Task 2: Configure a Static Route Using the Outgoing Interface on R1
On R1, configure a static route to R2's LAN using R1's serial interface as the outgoing interface, rather than a next-hop address.
Task 3: Configure the Equivalent Route on R2
On R2, configure a static route to R1's LAN using the same interface-based syntax.
Task 4: Verify Connectivity
Confirm R1 can reach R2's LAN and vice versa.
Task 5: Examine the Routing Table Entry
Note how the route appears differently in the routing table compared to a next-hop-based static route.
Solution and Verification
R1(config)# interface serial0/0/0
R1(config-if)# ip address 10.20.20.1 255.255.255.252
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# interface loopback1
R1(config-if)# ip address 192.168.10.1 255.255.255.0R2(config)# interface serial0/0/0
R2(config-if)# ip address 10.20.20.2 255.255.255.252
R2(config-if)# clock rate 64000
R2(config-if)# no shutdown
R2(config-if)# exit
R2(config)# interface loopback1
R2(config-if)# ip address 192.168.20.1 255.255.255.0R1(config)# ip route 192.168.20.0 255.255.255.0 serial0/0/0
-- The outgoing interface (serial0/0/0) is
-- specified instead of R2's serial IP addressR2(config)# ip route 192.168.10.0 255.255.255.0 serial0/0/0R1# ping 192.168.20.1
!!!!!
Success rate is 100 percent (5/5)R1# show ip route static
S 192.168.20.0/24 is directly connected, Serial0/0/0
-- Notice the route is listed as "directly
-- connected" rather than "via" a next-hop
-- address -- this is a distinguishing
-- characteristic of interface-based static
-- routes, since the router treats the entire
-- destination network as reachable directly
-- out that interfaceKey Takeaway
Interface-based static routes work well on true point-to-point links like this serial connection, since there is only one possible destination for anything sent out that interface. On a multi-access network like Ethernet, however, this same syntax forces the router to ARP for every destination address individually rather than just the next hop, creating unnecessary overhead — next-hop-based static routes are generally preferred except on genuinely point-to-point media.