The user uses the USG2120BSR to connect to the third-party router through the serial port. The link-layer is Up, but the protocol-layer is Down.
1. Query the information about the port.
Serial2/0/0 current state : UP
Line protocol current state : UP
Description : Huawei Symantec, Secospace Series, Serial2/0/0 Interface
The Maximum Transmit Unit is 1500 bytes, Hold timer is 10(sec)
Internet Address is unnumbered, using address of Vlanif11(184.108.40.206/24)
Link layer protocol is PPP
LCP opened, IPCP acksent
Output queue : (Urgent queue : Size/Length/Discards) 0/50/0
Output queue : (Protocol queue : Size/Length/Discards) 0/1000/0
Output queue : (FIFO queuing : Size/Length/Discards) 0/256/0
Physical layer is synchronous,
Interface is DTE, Clock is DTECLK1, Cable type is V35
Last 300 seconds input rate 0.00 bytes/sec, 0.00 packets/sec
Last 300 seconds output rate 0.00 bytes/sec, 0.00 packets/sec
Input: 679 packets, 9814 bytes
109 non octet_aligned, 2 abort sequence
0 giants, 4 CRC, 0 overruns, 0 carrier lost
Output:666 packets, 10996 bytes
0 underruns, 0 CTS lost errors
DCD=UP DTR=UP DSR=UP RTS=UP CTS=UP
The contents in red indicate that the status of the IPCP is abnormal. Therefore, the PPP negotiation fails.
2. Query the debugging information of the PPP. It is discovered that the peer router cannot identify the negotiation packets sent by the device of Huawei Symantec
2. Configure two commands on the serial port.
undo ppp ipcp nbns request
undo ppp dns nbns request
The problem is solved.
The PPP negotiation fails.