The fault phenomenon

There are multiple users in a dormitory building applying for repair , After the field survey, it was found that the indoor incoming line connecting host could not obtain the address , Physical circuit connection . Because during the holiday , Only a few users stay in school , It is uncertain whether all users of the building are unable to access the Internet .

Networking information

Pictured , Two access switches are cascaded , Models for H3C S5152-EI

Check the information

stay H3C-1 Check the following information on ：

View interface status （display interface brief）, There is no interface ADM Down（ managed Down）;

Check two devices dhcp And dhcp snooping Enabling situation , All normal ;

View the... Of two devices Vlan And Trunk Mouth cutting , Business Vlan And management Vlan All released ;

see LLDP Information ：

[XXXX-H3C-1]dis lldp nei li
Chassis ID : * -- -- Nearest nontpmr bridge neighbor
             # -- -- Nearest customer bridge neighbor
             Default -- -- Nearest bridge neighbor
System Name          Local Interface Chassis ID      Port ID
XXXX-H3C-2           GE1/0/16        0440-a93b-9a98  GigabitEthernet1/0/42            
XXXXXXX-HJ-5750H-02  GE1/0/50        5869-6c63-712b  Gi0/22                     
XXXX-H3C-2           GE1/0/52        0440-a93b-9a98  GigabitEthernet1/0/49      
[XXXX-H3C-1]

Except for the upper level convergence , There are actually two neighbors at the next level Local Interface

among Gigabitethernet 1/0/52 Gigabit optical port , Therefore, there must be other cables between the two switches to cause the loop .

Check the relevant port logs （ And Baidu notes ）：

H3C-1：

[XXXX-H3C-1]dis log | inc 1/0/16
STP/6/STP_DETECTED_TC: Instance 0's port GigabitEthernet1/0/16 detected a topology change.
// It indicates that the spanning tree topology changes on this port （ Added new devices ）

LLDP/5/LLDP_PVID_INCONSISTENT: PVID mismatch discovered on GigabitEthernet1/0/16 (PVID 1121), with NY02-H3C-2 GigabitEthernet1/0/42 (PVID 1194).
// This port is the same as the port of the neighbor device Vlan ID atypism 

LLDP/6/LLDP_CREATE_NEIGHBOR: Nearest bridge agent neighbor created on port GigabitEthernet1/0/16 (IfIndex 16), neighbor's chassis ID is 0440-a93b-9a98, port ID is GigabitEthernet1/0/42.
//LLDP Add new neighbors to the table 

STP/6/STP_NOTIFIED_TC: Instance 0's port GigabitEthernet1/0/16 was notified a topology change.
// Topology change under this port 

Deleted time （ Because Ya is not allowed at all ,dis clock still 2013-01-01, In connection with NTP Please be spicy ）

Interface and protocol are deleted up/down Log entries

Keep only one frequently occurring log entry , Such as Instance 0's port GigabitEthernet1/0/16 detected a topology change.

H3C Does the official website not provide log query function now …… Give keywords and don't return results , It's still unclear STP/6/STP_DETECTED_TC And STP/6/STP_NOTIFIED_TC The relationship between

H3C-2：

[XXXX-H3C-2]dis log | inc 1/0/42
STP/6/STP_DETECTED_TC: Instance 0's port GigabitEthernet1/0/42 detected a topology change.

STP/6/STP_NOTIFIED_TC: Instance 0's port GigabitEthernet1/0/42 was notified a topology change.

LLDP/5/LLDP_PVID_INCONSISTENT: PVID mismatch discovered on GigabitEthernet1/0/42 (PVID 1194), with NY02-H3C-1 GigabitEthernet1/0/16 (PVID 1121).

LLDP/6/LLDP_CREATE_NEIGHBOR: Nearest bridge agent neighbor created on port GigabitEthernet1/0/42 (IfIndex 42), neighbor's chassis ID is 0440-a93b-93d8, port ID is GigabitEthernet1/0/16.

LLDP/6/LLDP_DELETE_NEIGHBOR: Nearest bridge agent neighbor deleted on port GigabitEthernet1/0/42 (IfIndex 42), neighbor's chassis ID is 0440-a93b-93d8, port ID is GigabitEthernet1/0/16.

STP/5/STP_BPDU_RECEIVE_EXPIRY: Instance 0's port GigabitEthernet1/0/42 received no BPDU within the rcvdInfoWhile interval. Information of the port aged out.
// The unspecified port is BPDU No... Was received before the timeout BPDU message , The port state changes , It is recommended to check the uplink device STP Status and whether there is malicious attack 

speculation

2 In addition to the normal optical fiber cascade between switches , There is also a line cascade , Probably ：

H3C-1-Gigabitethernet1/0/16- Distribution frame - Dormitory incoming line - Dormitory branch exchange - Another dormitory incoming line （？）- Distribution frame -H3C-2-Gigabitethernet1/0/42

It sounds ridiculous , I don't know exactly how to wire or how to network in the user room , But as far as the current information is concerned , Such speculation seems to be the most reasonable

Handle

take H3C-1 Of Gigabitethernet1/0/16 Mouth closed

[XXXX-H3C-1]int GigabitEthernet 1/0/16
[XXXX-H3C-1-GigabitEthernet1/0/16]shutdown

After that , Look again LLDP state , normal , Ask the repair user of the building , The network has been restored

[XXXX-H3C-1]dis lldp nei li
Chassis ID : * -- -- Nearest nontpmr bridge neighbor
             # -- -- Nearest customer bridge neighbor
             Default -- -- Nearest bridge neighbor
System Name          Local Interface Chassis ID      Port ID         
XXXXXXX-HJ-5750H-02  GE1/0/50        5869-6c63-712b  Gi0/22                     
XXXX-H3C-2           GE1/0/52        0440-a93b-9a98  GigabitEthernet1/0/49  

Observe H3C-2 Of Gigabitethernet 1/0/42 mouth , The status light remains on

At this time, it is speculated that the cable enters the branch exchange in the user's room , Only keep the line unobstructed , Users can also use the network normally

Check the lines of the relevant ports of the two devices VCT

H3C-1

[XXXX-H3C-1]int GigabitEthernet 1/0/16
[XXXX-H3C-1-GigabitEthernet1/0/16]virtual-cable-test 
Cable status: abnormal(open), 11 metre(s) // Open the way , The port to the abnormal position is 11m
Pair Impedance mismatch: no
Pair skew: - ns
Pair swap: -
Pair polarity: -
Insertion loss: - db
Return loss: - db
Near-end crosstalk: - db

H3C-2

[XXXX-H3C-2]int GigabitEthernet 1/0/42
[XXXX-H3C-2-GigabitEthernet1/0/42]virtual-cable-test 
Cable status: normal, 55 metre(s)
Pair Impedance mismatch: no
Pair skew: - ns
Pair swap: -
Pair polarity: -
Insertion loss: - db
Return loss: - db
Near-end crosstalk: - db

Although this command is not very useful , But the author thought that if these two lines lead to a small switch , The cable length should be consistent , One of the results turned out to be Abnormal……

Let's quote briefly ：

“ Open circuit refers to the partial disconnection of one or more wires in the network cable , This phenomenon is generally caused by physical external forces ; There are two cases of short circuit , One is to short circuit two wires in one wire pair , One is a short circuit between two wires ; Reverse connection refers to the process of termination , Connect the same pair of wires reversely at the needle positions at both ends of the network cable ; Wrong or right refers to connecting a pair of wires to the opposite end of the line ; Crosstalk refers to the separation of the original two pairs of wires , Reconstitute the pair , In this case , Whether the copper cable has on-off fault , The multimeter can't detect , It is necessary to use a dedicated network cable tester to detect , The crosstalk signal passes through the cable , It will cause serious near end crosstalk .”

come from The network tester detects the cause of network cable failure

Reference resources Ethernet cable RJ45 When wiring 5 Detailed explanation of all kinds of faults

I don't know where to study after thinking about it , If open circuit is displayed , Estimation is 4、5、7、8 The wired core is blocked ？（ It's a pity not to have a test , Have a chance to test again ）

Add

Let's take a brief look at the user oriented port configuration of these two access switches ：

[XXXX-H3C-1]int GigabitEthernet 1/0/16
[XXXX-H3C-1-GigabitEthernet1/0/16]dis this
#
interface GigabitEthernet1/0/16
 port access vlan 1121
 shutdown
 port-isolate enable group 1
 loopback-detection action shutdown
#
return

（ Actually, I have seen the configuration for a long time , Just put it later ）

It must be mentioned that loopback-detection action shutdown、stp edged-port、stp bpdu protection The relationship and difference between

In two devices , It's all enabled

 loopback-detection global action shutdown
 loopback-detection interval-time 35

stp bpdu-protection
stp global enable

Loop detection technology Loopback Detection It sends a special message periodically from the interface Detection message , Then check whether the message is returned to the device （ Don't ask for it 、 The sending interface is the same interface ）, And then judge the interface 、 Whether there is a loop between the network or equipment under the equipment and the dual interfaces of the equipment Loopback Detection To configure - S2750, S5700, S6700 V200R005(C00&C01&C02&C03) Configuration Guide - Ethernet switching - Huawei

This command can only query this device Whether it is self looping （ Only associated with broadcast storms , Spanning tree calculation is not involved ） , and stp edged-port Applicable to the service port of the access switch （ Connecting terminals ）, Coordinate with the overall situation stp bpdu-protection Break the ring .

Strangely, both devices are enabled globally BPDU Protect , However, in the above case, there is no trigger mechanism to close the port , It's really strange , If you want to check carefully again, it is estimated that you will have to grab the bag or repeat the experiment , At present, we have to set all business interfaces as edge ports .

It can only be said that it is difficult to solve the problem , It is not easy to see the essence through problems , If a big man sees this article , Comments and criticisms are welcome , If the younger brother makes progress in technology in the future or repeats the phenomenon , Just write another blog post as a supplement to this article , First BiliBili Watch the house dance .