324 CHAPTER 20: CONFIGURING IP ADDRESS
2Configure router R1 of Shenzhen subsidiary:
[Router-Ethernet0] ip address 172.16.20.1 255.255.255.0
aBorrow IP address of Ethernet
[Router-Serial0] ip address unnumbered Ethernet0
[Router-Serial0] link-protocol ppp
bConfigure routing to Ethernet segment on Beijing router R, this routing is
default routing
[Router] ip route-static 0.0.0.0 0.0.0.0 172.16.10.1
cConfigure interface routing to serial port of Beijing router R
[Router] ip route-static 172.16.10.1 255.255.255.255 serial0
Two static routing must be configured on Beijing headquarters router R to ensure
access to Ethernet host of Shenzhen router R1.
The first static routing is to Ethernet segment of R1: the next hop is the IP address
of serial port of R1 (or an unnumbered IP address)
ip route-static 172.16.20.1 255.255.255.0 172.16.20.1
The second static route is an interface route to the serial port of R1, and the next
hop is the serial port of R
ip route-static 172.16.20.1 255.255.255.255 serial 0
After the two routes are added, router R will be able to forward the IP message to
R1 correctly
Similarly, two static routes must be configured on R1 to access the Ethernet
segment of router R. The first static routing is to Ethernet segment of R: the next
hop is the IP address of serial port of R (or an unnumbered IP address)
ip route-static 0.0.0.0 0.0.0.0 172.16.10.1
The second static route is an interface route to the serial port of R, and the next
hop is the serial port of R1.
ip route-static 172.16.10.1 255.255.255.255 serial0
The configuration of R2 and R3 is similar to that of R1.
Troubleshooting IP
Address Configuration A router is a network interconnection device. So when IP address for an interface
is configured, networking requirements and sub-net classification should be
known. Normally, the following rules should be observed:
■The master IP address of a router Ethernet interface must be in the same
network segment with the LAN to which this Ethernet interface is connected.
■Serial port IP addresses of the routers at both ends of WAN must be in the
same network segment.
Fault 1: The router cannot ping through a certain host in LAN
Troubleshooting; First check if the IP address configuration of the router's Ethernet
interface and the host in LAN are in the same network segment
If the configuration is correct, turn on the arp debugging switch on the router, and
check if the router can correctly send and receive arp messages. If it can send but