对于RT1的配置：

<RT1>display interface Serial 0/1/0
Serial0/1/0 current state: UP
Line protocol current state: UP
Description: Serial0/1/0 Interface
The Maximum Transmit Unit is 1500, Hold timer is 10(sec)
Internet protocol processing : disabled
Link layer protocol is PPP
LCP opened
Output queue : (Urgent queuing : Size/Length/Discards)  0/100/0
Output queue : (Protocol queuing : Size/Length/Discards)  0/500/0
Output queue : (FIFO queuing : Size/Length/Discards)  0/75/0
Interface is V35
    17 packets input,  210 bytes
    18 packets output,  224 bytes

<RT1>system-view

System View: return to User View with Ctrl+Z.

[RT1]interface serial 0/1/0

[RT1-serial0/1/0]link-protocol HDLC

%Dec  7 20:39:53:852 2014 RT1 IFNET/3/LINK_UPDOWN: Serial0/1/0 link status is DOWN.
%Dec  7 20:39:53:868 2014 RT1 IFNET/5/LINEPROTO_UPDOWN: Line protocol on the interface Serial0/1/0 is DOWN.
%Dec  7 20:39:53:868 2014 RT1 IFNET/3/LINK_UPDOWN: Serial0/1/0 link status is UP.

[RT1-Serial0/1/0]ip address 10.1.1.1 30 

[RT1-Serial0/1/0]return

<RT1>display interface Serial 0/1/0

Serial0/1/0 current state: UP
Line protocol current state: DOWN
Description: Serial0/1/0 Interface
The Maximum Transmit Unit is 1500, Hold timer is 10(sec)
Internet Address is 10.1.1.1/30 Primary
Link layer protocol is HDLC
Output queue : (Urgent queuing : Size/Length/Discards)  0/100/0
Output queue : (Protocol queuing : Size/Length/Discards)  0/500/0
Output queue : (FIFO queuing : Size/Length/Discards)  0/75/0
Interface is V35
    107 packets input,  1318 bytes
    86 packets output,  1340 bytes

此时类似的配置RT2，接口IP设置10.1.1.2   在输入<RT2>display interface Serial 0/1/0会看到此时的Line protocol current state 再次UP

Serial0/1/0 current state: UP
Line protocol current state: UP
Description: Serial0/1/0 Interface
The Maximum Transmit Unit is 1500, Hold timer is 10(sec)
Internet Address is 10.1.1.2/30 Primary
Link layer protocol is HDLC
Output queue : (Urgent queuing : Size/Length/Discards)  0/100/0
Output queue : (Protocol queuing : Size/Length/Discards)  0/500/0
Output queue : (FIFO queuing : Size/Length/Discards)  0/75/0
Interface is V35
    127 packets input,  2250 bytes
    163 packets output,  2310 bytes

然后在RT1中输入ping命令看是否与RT2连通

<RT1>ping 10.1.1.2

PING 10.1.1.2: 56  data bytes, press CTRL_C to break
    Reply from 10.1.1.2: bytes=56 Sequence=1 ttl=255 time=20 ms
    Request time out
    Reply from 10.1.1.2: bytes=56 Sequence=3 ttl=255 time=10 ms
    Reply from 10.1.1.2: bytes=56 Sequence=4 ttl=255 time=10 ms
    Reply from 10.1.1.2: bytes=56 Sequence=5 ttl=255 time=4 ms


  --- 10.1.1.2 ping statistics ---
    5 packet(s) transmitted
    4 packet(s) received
    20.00% packet loss
    round-trip min/avg/max = 4/11/20 ms