3Com MSR 50 Series Configuration Manual page 629

Network diagram
Figure 188 Network diagram for IP unnumbered configuration
DDN
S 2 / 1
Router A
Eth 1 / 1
172 . 16 . 10 . 1 / 24
Configuration procedure
1 Configure Router A
# Assign a primary IP address to Ethernet1/1.
<RouterA> system-view
[RouterA] interface ethernet 1/1
[RouterA-Ethernet1/1] ip address 172.16.10.1 255.255.255.0
[RouterA-Ethernet1/1] quit
# Configure Serial2/1 to borrow an IP address from Ethernet1/1.
[RouterA] interface serial 2/1
[RouterA-Serial2/1] ip address unnumbered interface ethernet 1/1
[RouterA-Serial2/1] quit
# Create a route to the Ethernet segment attached to Router B, specifying
interface Serial2/1 as the outgoing interface.
[RouterA] ip route-static 172.16.20.0 255.255.255.0 serial 2/1
2 Configure Router B
# Assign a primary IP address to Ethernet1/1.
<RouterB> system-view
[RouterB] interface ethernet 1/1
[RouterB-Ethernet1/1] ip address 172.16.20.1 255.255.255.0
[RouterB-Ethernet1/1] quit
# Configure interface Serial2/1 to borrow an IP address from Ethernet1/1.
[RouterB] interface serial 2/1
[RouterB-Serial2/1] ip address unnumbered interface ethernet 1/1
[RouterB-Serial2/1] quit
# Create a route to the Ethernet segment attached to Router A, specifying
interface Serial2/1 as the outgoing interface.
[RouterB] ip route-static 172.16.10.0 255.255.255.0 serial 2/1
S 2 / 1
Router B
Eth 1 / 1
172 . 16 . 20 . 1 / 24
Configuring IP Unnumbered 629