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STP Timers, BPDU Comparing Principle in STP mode

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 Port: Port 3 is the root port of switch B and port 5 is the root port of switch C; port 1 is the designated port of switch A and port 4 is the designated port of switch B; port 6 is the blocked port of switch C. Figure 7-1 Basic STP diagram  STP Timers Hello Time: Hello Time ranges from 1 to 10 seconds. It specifies the interval to send BPDU packets. It is used to test the links. Max. Age: Max. Age ranges from 6 to 40 seconds. It specifies the maximum time the switch can wait without receiving a BPDU before attempting to reconfigure. Forward Delay: Forward Delay ranges from 4 to 30 seconds. It specifies the time for the port to transit its state after the network topology is changed. When the STP regeneration caused by network malfunction occurs, the STP structure will get some corresponding change. However, as the new configuration BPDUs cannot be spread in the whole network at once, the temporal loop will occur if the port transits its state immediately. Therefore, STP adopts a state transit mechanism, that is, the new root port and the designated port begins to forward data after twice forward delay, which ensures the new configuration BPDUs are spread in the whole network.  BPDU Comparing Principle in STP mode Assuming two BPDUs: BPDU X and BPDU Y If the root bridge ID of X is smaller than that of Y, X is superior to Y. If the root bridge ID of X equals that of Y, but the root path cost of X is smaller than that of Y, X is superior to Y. If the root bridge ID and the root path cost of X equal those of Y, but the bridge ID of X is smaller than that of Y, X is superior to Y. If the root bridge ID, the root path cost and bridge ID of X equal those of Y, but the port ID of X is smaller than that of Y, X is superior to Y. 64

Section	Page
Package Contents	9
Chapter 1 About this Guide	10
1.1 Intended Readers	10
1.2 Conventions	10
1.3 Overview of This Guide	10
Chapter 2 Introduction	13
2.1 Overview of the Switch	13
2.2 Main Features	13
2.3 Appearance Description	14
2.3.1 Front Panel	14
2.3.2 Rear Panel	15
Chapter 3 Login to the Switch	16
3.1 Login	16
3.2 Configuration	16
Chapter 4 System	18
4.1 System Info	18
4.1.1 System Summary	18
4.1.2 Device Description	20
4.1.3 System Time	20
4.1.4 Daylight Saving Time	21
4.1.5 System IP	23
4.2 User Management	24
4.2.1 User Table	24
4.2.2 User Config	24
4.3 System Tools	26
4.3.1 Config Restore	26
4.3.2 Config Backup	26
4.3.3 Firmware Upgrade	27
4.3.4 System Reboot	28
4.3.5 System Reset	28
4.4 Access Security	28
4.4.1 Access Control	29
4.4.2 SSL Config	30
4.4.3 SSH Config	31
Chapter 5 Switching	37
5.1 Port	37
5.1.1 Port Config	37
5.1.2 Port Mirror	38
5.1.3 Port Security	40
5.1.4 Port Isolation	42
5.1.5 Loopback Detection	43
5.2 LAG	44
5.2.1 LAG Table	45
5.2.2 Static LAG	46
5.2.3 LACP Config	47
5.3 Traffic Monitor	49
5.3.1 Traffic Summary	49
5.3.2 Traffic Statistics	50
5.4 MAC Address	52
5.4.1 Address Table	53
5.4.2 Static Address	54
5.4.3 Dynamic Address	55
5.4.4 Filtering Address	57
5.5 DHCP Filtering	58
Chapter 6 VLAN	62
6.1 802.1Q VLAN	63
6.1.1 VLAN Config	65
6.1.2 Port Config	67
6.2 Application Example for 802.1Q VLAN	69
Chapter 7 Spanning Tree	71
7.1 STP Config	76
7.1.1 STP Config	76
7.1.2 STP Summary	78
7.2 Port Config	78
7.3 MSTP Instance	80
7.3.1 Region Config	80
7.3.2 Instance Config	81
7.3.3 Instance Port Config	82
7.4 STP Security	84
7.4.1 Port Protect	84
7.4.2 TC Protect	87
7.5 Application Example for STP Function	87
Chapter 8 Multicast	91
8.1 IGMP Snooping	93
8.1.1 Snooping Config	94
8.1.2 Port Config	95
8.1.3 VLAN Config	96
8.1.4 Multicast VLAN	98
8.2 Multicast IP	101
8.2.1 Multicast IP Table	101
8.2.2 Static Multicast IP	102
8.3 Multicast Filter	103
8.3.1 IP-Range	103
8.3.2 Port Filter	104
8.4 Packet Statistics	106
Chapter 9 QoS	108
9.1 DiffServ	111
9.1.1 Port Priority	111
9.1.2 DSCP Priority	112
9.1.3 802.1P/CoS mapping	113
9.1.4 Schedule Mode	114
9.2 Bandwidth Control	115
9.2.1 Rate Limit	115
9.2.2 Storm Control	116
9.3 Voice VLAN	118
9.3.1 Global Config	120
9.3.2 Port Config	120
9.3.3 OUI Config	122
Chapter 10 PoE	124
10.1 PoE Config	124
10.1.1 PoE Config	125
10.1.2 PoE Profile	126
10.2 PoE Time-Range	127
10.2.1 Time-Range Summary	127
10.2.2 PoE Time-Range Create	128
10.2.3 PoE Holiday Config	129
Chapter 11 SNMP	130
11.1 SNMP Config	132
11.1.1 Global Config	132
11.1.2 SNMP View	133
11.1.3 SNMP Group	134
11.1.4 SNMP User	135
11.1.5 SNMP Community	137
11.2 Notification	139
11.3 RMON	141
11.3.1 History Control	142
11.3.2 Event Config	142
11.3.3 Alarm Config	143
Chapter 12 LLDP	146
12.1 Basic Config	150
12.1.1 Global Config	150
12.1.2 Port Config	151
12.2 Device Info	152
12.2.1 Local Info	152
12.2.2 Neighbor Info	153
12.3 Device Statistics	153
12.4 LLDP-MED	155
12.4.1 Global Config	156
12.4.2 Port Config	156
12.4.3 Local Info	158
12.4.4 Neighbor Info	159
Chapter 13 Maintenance	161
13.1 System Monitor	161
13.1.1 CPU Monitor	161
13.1.2 Memory Monitor	162
13.2 Log	162
13.2.1 Log Table	163
13.2.2 Local Log	164
13.2.3 Remote Log	165
13.2.4 Backup Log	165
13.3 Device Diagnostics	166
13.3.1 Cable Test	166
13.3.2 Loopback	167
13.4 Network Diagnostics	168
13.4.1 Ping	168
13.4.2 Tracert	168
Appendix A: Specifications	170
Appendix B: Configuring the PCs	171

Match case Limit results 1 per page



Port: Port 3 is the root port of switch B and port 5 is the root port of switch C; port 1 is the

designated port of switch A and port 4 is the designated port of switch B; port 6 is the blocked

port of switch C.

Figure 7-1 Basic STP diagram



STP Timers

Hello Time:

Hello Time ranges from 1 to 10 seconds. It specifies the interval to send BPDU packets. It is used

to test the links.

Max. Age:

Max. Age ranges from 6 to 40 seconds. It specifies the maximum time the switch can wait without

receiving a BPDU before attempting to reconfigure.

Forward Delay:

Forward Delay ranges from 4 to 30 seconds. It specifies the time for the port to transit its state

after the network topology is changed.

When the STP regeneration caused by network malfunction occurs, the STP structure will get

some corresponding change. However, as the new configuration BPDUs cannot be spread in the

whole network at once, the temporal loop will occur if the port transits its state immediately.

Therefore, STP adopts a state transit mechanism, that is, the new root port and the designated

port begins to forward data after twice forward delay, which ensures the new configuration BPDUs

are spread in the whole network.



BPDU Comparing Principle in STP mode

Assuming two BPDUs: BPDU X and BPDU Y

If the root bridge ID of X is smaller than that of Y, X is superior to Y.

If the root bridge ID of X equals that of Y, but the root path cost of X is smaller than that of Y, X is

superior to Y.

If the root bridge ID and the root path cost of X equal those of Y, but the bridge ID of X is smaller

than that of Y, X is superior to Y.

If the root bridge ID, the root path cost and bridge ID of X equal those of Y, but the port ID of X is

smaller than that of Y, X is superior to Y.