Information Technology Reference
In-Depth Information
If possible, establish a separate terminal session by consoling into R2 from another work-
station. Doing this allows you to observe the debug output on R1 when you make changes
on R2. You can also use the
debug ip routing
command on R2.
Step 8.
R2#
debug ip routing
IP routing debugging is on
Enter interface configuration mode for R2's WAN interface connected to R1.
R2#
configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#
interface serial 0/0/0
Configure the IP address as specified in the topology diagram.
R2(config-if)#
ip address 172.16.2.2 255.255.255.0
is_up: 0 state: 6 sub state: 1 line: 0
Enter the command necessary to ensure that the interface is fully configured.
Step 9.
If you are not sure what the correct command is, review the section “Configuring and
Verifying Interfaces Exercise,” earlier in this chapter.
R2(config-if)#
no shutdown
After you enter the correct command, you should see debug output similar to the following
example:
is_up: 0 state: 4 sub state: 1 line: 0
%LINK-3-UPDOWN: Interface Serial0/0/0, changed state to up
is_up: 1 state: 4 sub state: 1 line: 0
RT: add 172.16.2.0/24 via 0.0.0.0, connected metric [0/0]
RT: interface Serial0/0/0 added to routing table
is_up: 1 state: 4 sub state: 1 line: 0
%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/0, changed state
to up
is_up: 1 state: 4 sub state: 1 line: 0
The new network that you configured on the WAN interface is now added to the routing
table, as shown in the highlighted output.
If you do not see the route added to the routing table, the interface did not come up. Use
the following systematic process to troubleshoot your connection:
Check your physical connections between the two WAN interfaces for R1 and R2.
1.
Is the correct interface attached?
yes
Your router has more than one WAN interface. Did you connect the correct WAN
interface?
yes
An interface will not come up unless it detects a link beat at the physical layer from
another device. Is the interface connected to the other router's interface?
yes
