Hello, everyone!
This post is about the issue that the protocol status of a PPP interface is down. Please see more details as you read further down.
1.Common Causes
After an interface is configured with PPP, LCP negotiation fails, which causes the protocol status of the interface to be Down.
This fault is commonly caused by one of the following:
l PPP configurations on the two ends of the link are incorrect.
l The physical status of the interface is Down.
l PPP packets are discarded.
l A loop occurs on the link.
l The link delay is too long.
2.Troubleshooting Flowchart
The troubleshooting roadmap is as follows:
l Check that PPP configurations on the two ends of the link are correct.
l Check that the physical status of the interface is Up.
l Check that the interface can sent and receive protocol packets.
l Check that the link is loop-free.
l Check that the link delay is tolerant.
Figure 1-1 shows the troubleshooting flowchart.
Figure 1-1 Troubleshooting flowchart for an LCP negotiation failure
3.Troubleshooting Procedure
Saving the results of each troubleshooting step is recommended. If your troubleshooting fails to correct the fault, you will have a record of your actions to provide Huawei technical support personnel.
Procedure
Step 1 Check that PPP configurations on the two ends of the link are correct.
Run the display this command in the view of the interface whose protocol status is Down to check PPP configurations.
[Huawei-Serial2/0/0] display this
#
interface Serial2/0/0
link-protocol ppp
undo shutdown
ip address 10.10.1.1 255.255.255.0
#
return
l Check whether the following configurations on the two ends match each other. If not, modify the configuration referring to the chapter "PPP and MP Configuration" in the AR100&AR120&AR150&AR160&AR200&AR1200&AR2200&AR3200&AR3600Configuration Guide - WAN Access.
− Check whether the authenticator and authenticatee are configured with the same authentication mode. The ppp authentication-mode authentication-modecommand indicates the authentication mode adopted by the local end that functions as the authenticator. You need to check the authentication mode adopted by the peer. For example, if the ppp pap local-user user-namepassword simple password command has been configured, it means that the peer adopts PAP authentication.
− Check whether both ends are bundled into an MP-group or neither of the two ends is bundled into an MP-group. If one end has been bundled into an MP-group, the other end must be bundled into the same MP-group. If the ppp mp interface-type interface-number command is configured, it means that the interface has been bundled into an MP-group.
− Check whether the authenticator and authenticatee are configured with the same password for PPP authentication.
n If PAP authentication is adopted, do as follows to check the configured user name and password:
Check the user name and password of the authenticatee in the interface view.
[Huawei-Serial2/0/0] display this
#
interface Serial2/0/0
link-protocol ppp
ppp pap local-user huawei password simple huawei
undo shutdown
#
return
Check the user name and password of the authenticator in the AAA view.
[Huawei] aaa
[Huawei-aaa] display this
#
aaa
local-user huawei password cipher
%$%$t"}TJ~\;SKu%wY$mKGdY%*!u%$%$
#
return
n If the authenticator adopts CHAP authentication and is configured with a user name, do as follows to check the user name and password:
Check the user name of the authenticatee in the interface view, and then check the password in the AAA view based on the user name.
[Huawei-Serial2/0/0] display this
#
interface Serial2/0/0
link-protocol ppp
ppp chap user huawei
undo shutdown
#
return
[Huawei-Pos1/0/0] aaa
[Huawei-aaa] display this
#
aaa
local-user huawei password cipher
%$%$t"}TJ~\;SKu%wY$mKGdY%*!u%$%$
#
return
Check the user name and password of the authenticator in the AAA view.
[Huawei] aaa
[Huawei-aaa] display this
#
aaa
local-user huawei password cipher
%$%$t"}TJ~\;SKu%wY$mKGdY%*!u%$%$
#
return
n If the authenticator adopts CHAP authentication but is not configured with a user name, do as follows to check the user name and password:
Check the user name and password of the authenticatee in the interface view.
[Huawei-Serial2/0/0] display this
#
interface Serial2/0/0
link-protocol ppp
ppp chap user huawei
ppp chap password simple huawei
undo shutdown
#
return
Check the user name and password of the authenticator in the AAA view.
[Huawei] aaa
[Huawei-aaa] display this
#
aaa
local-user huawei password cipher
%$%$t"}TJ~\;SKu%wY$mKGdY%*!u%$%$
#
return
l If the preceding configurations are correct but the fault persists, go to Step 2.
Step 2 Check that the physical status of the interface is Up.
Run the display interface interface-type interface-numbercommand to check the physical status of the interface.
l If the physical status of the interface is Down, you need to rectify the physical fault of the interface. For detailed troubleshooting procedures, see "Physical Interconnection Troubleshooting".
l If the physical status of the interface is Up but the fault persists, go to Step 3.
Step 3 Check that the interface can sent and receive protocol packets.
Run the display interface interface-type interface-numbercommand to check the number of sent packets and received packets to determine whether the interface sends and receives protocol packets.
[Huawei] display interface Serial 2/0/0
Serial2/0/0 current state : UP
Line protocol current state : UP
Last line protocol up time : 2010-02-04 22:35
Description:HUAWEI, AR Series, Serial2/0/0 Interface
Route Port,The Maximum Transmit Unit is 4470, Hold timer is 10(sec)
Internet Address is 108.108.1.1/24
Link layer protocol is PPP
LCP opened, IPCP opened
The Vendor PN is HFBR-57E0P
The Vendor Name is AVAGO
Port BW: 155M, Transceiver max BW: 155M, Transceiver Mode: MultiMode
WaveLength: 1310nm, Transmission Distance: 2000m
Physical layer is Packet Over SDH
Scramble enabled, clock master, CRC-32, loopback: none
Flag J0 "NetEngine "
Flag J1 "NetEngine "
Flag C2 22(0x16)
SDH alarm:
section layer: none
line layer:
none
path layer:
none
SDH error:
section layer: B1 0
line layer:
B2 0 REI 44
path layer:
B3 0 REI 23
Statistics last cleared:never
Last 300 seconds input rate 24 bits/sec, 0 packets/sec
Last 300 seconds output rate 24 bits/sec, 0 packets/sec
Input: 70945 packets, 1135144 bytes
Input error: 0 shortpacket, 0 longpacket, 0 CRC, 0
lostpacket
Output: 70945 packets, 1135140 bytes
Output error: 0 lostpackets
Output error: 0 overrunpackets, 0
underrunpackets
l If the number of received or sent packets is 0, or the number does not increase, it indicates that packets are discarded during transmission. Check whether the physical connection is correct. For detailed information, see "Physical Interface Cannot Go Up".
l If the physical connection is correct, you need to locate the cause of packet loss. For detailed troubleshooting procedures, see "Packet Loss Troubleshooting".
l If packets can be received and sent but the fault persists, go toStep 4.
Debugging affects the system performance. Therefore, after debugging, run the undo debugging allcommand to disable it immediately.
In addition, you can run the debugging ppp all interfaceinterface-type interface-number command to check the number of sent and received protocol packets and the status changes of the PPP state machine.
Jun 2 2010 17:19:41.310.1 Huawei
PPP/7/debug2:Slot=1;
PPP Event:
Serial2/0/0 LCP TO+(Timeout with counter >
0) Event
state acksent , Retransmit = 4
Jun 2 2010 17:19:41.310.2 Huawei PPP/7/debug2:Slot=1;
PPP Packet:
Serial2/0/0 Output LCP(c021) Pkt, Len 18
State acksent, code ConfReq(01), id 3, len 14
MRU(1), len 4, val 1176
MagicNumber(5), len 6, val 00abb891
Jun 2 2010 17:19:41.310.1 Huawei PPP/7/debug2:Slot=1;
PPP Packet:
Serial2/0/0 Input LCP(c021) Pkt, Len 18
State acksent, code ConfAck(02), id 3, len 14
MRU(1), len 4, val 1176
MagicNumber(5), len 6, val 00abb891
Jun 2 2010 17:19:41.310.2 Huawei PPP/7/debug2:Slot=1;
PPP Event:
Serial2/0/0 LCP RCA(Receive Config Ack)
Event
state
acksent
Step 4 Check that the link is loop-free.
Run the display interface interface-type interface-numbercommand to check the physical status of the interface.
[Huawei] display interface Serial 2/0/0
Serial2/0/0 current state : UP
Line protocol current state : DOWN
Description:HUAWEI, AR Series, Serial 2/0/0 Interface
Route Port,The Maximum Transmit Unit is 4470, Hold timer is 10(sec)
Internet protocol processing : disabled
Link layer protocol is PPP, loopback is detected
LCP closed
The Vendor PN is HFBR-57E0P
The Vendor Name is AVAGO
Port BW: 155M, Transceiver max BW: 155M, Transceiver Mode: MultiMode
WaveLength: 1310nm, Transmission Distance: 2000m
Physical layer is Packet Over SDH
Scramble enabled, clock master, CRC-32, loopback: local
Flag J0 "NetEngine "
Flag J1 "NetEngine "
Flag C2 22(0x16)
SDH alarm:
section layer: none
line layer:
none
path layer:
none
SDH error:
section layer: B1 22
line layer:
B2 94 REI 145
path layer:
B3 44 REI 86
Statistics last cleared:never
Last 300 seconds input rate 56 bits/sec, 0 packets/sec
Last 300 seconds output rate 56 bits/sec, 0 packets/sec
Input: 40530 packets, 890400 bytes
Input error: 0 shortpacket, 0 longpacket, 2 CRC, 0
lostpacket
Output: 36512 packets, 946612 bytes
Output error: 0 lostpackets
Output error: 0 overrunpackets, 0 underrunpackets
l If loopback is detected is displayed, it indicates that a loop occurs on the link. You need to locate the cause of the loop and eliminate the loop.
l If no loop occurs but the fault persists, go to Step 5.
Step 5 Check that the link delay is tolerant.
Use a tester to test the link delay. On a Huawei router, the transmission of a PPP packet times out in 3 seconds, and the timeout period is configurable. The link delay must be smaller than the timeout period.
l If the link delay is too long, replace or maintain the relevant device.
l If the link delay is tolerant but the fault persists, go to Step 6.
Step 6 Collect the following information and contact technical support personnel.
l Results of the preceding troubleshooting procedure
l Configuration files, log files, and alarm files of the devices
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