3Com 3C17300A Implementation Guide - Page 46

STP Configurations, Configuration 1 - Redundancy for Backbone Link

Get 3Com 3C17300A - Switch 4200 PDF manuals and user guides
UPC - 662705493169
View all 3Com 3C17300A manuals
Add to My Manuals
Save this manual to your list of manuals

Page 46 highlights

46 CHAPTER 4: USING RESILIENCE FEATURES ■ Because Bridge A is the Root Bridge, it is also the Designated Bridge for LAN segment 1. Port 1 on Bridge A is therefore selected as the Designated Bridge Port for LAN Segment 1. ■ Port 1 of Bridges B, C, X and Y have been defined as Root Ports because they are the nearest to the Root Bridge and therefore have the most efficient path. ■ Bridges B and X offer the same Root Path Cost for LAN segment 2, however, Bridge B has been selected as the Designated Bridge for the segment because it has a lower Bridge Identifier. Port 2 on Bridge B is therefore selected as the Designated Bridge Port for LAN Segment 2. ■ Bridge C has been selected as the Designated Bridge for LAN segment 3, because it offers the lowest Root Path Cost for LAN Segment 3: ■ the route through Bridges C and B costs 200 (C to B=100, B to A=100) ■ the route through Bridges Y and B costs 300 (Y to B=200, B to A=100). Port 2 on Bridge C is therefore selected as the Designated Bridge Port for LAN Segment 3. STP Configurations Figure 11 shows three possible STP configurations using SuperStack 3 Switch units. ■ Configuration 1 - Redundancy for Backbone Link In this configuration, the Switches both have STP enabled and are connected by two links. STP discovers a duplicate path and blocks one of the links. If the enabled link breaks, the disabled link becomes re-enabled, therefore maintaining connectivity. ■ Configuration 2 - Redundancy through Meshed Backbone In this configuration, four Switch units are connected in a way that creates multiple paths between each one. STP discovers the duplicate paths and blocks two of the links. If an enabled link breaks, one of the disabled links becomes re-enabled, therefore maintaining connectivity. ■ Configuration 3 - Redundancy for Cabling Error In this configuration, a Switch has STP enabled and is accidentally connected to a hub using two links. STP discovers a duplicate path and blocks one of the links, therefore avoiding a loop.

  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10
  • 11
  • 12
  • 13
  • 14
  • 15
  • 16
  • 17
  • 18
  • 19
  • 20
  • 21
  • 22
  • 23
  • 24
  • 25
  • 26
  • 27
  • 28
  • 29
  • 30
  • 31
  • 32
  • 33
  • 34
  • 35
  • 36
  • 37
  • 38
  • 39
  • 40
  • 41
  • 42
  • 43
  • 44
  • 45
  • 46
  • 47
  • 48
  • 49
  • 50
  • 51
  • 52
  • 53
  • 54
  • 55
  • 56
  • 57
  • 58
  • 59
  • 60
  • 61
  • 62
  • 63
  • 64
  • 65
  • 66
  • 67
  • 68
  • 69
  • 70
  • 71
  • 72
  • 73
  • 74
  • 75
  • 76
  • 77
  • 78
  • 79
  • 80
  • 81
  • 82
  • 83
  • 84
  • 85
  • 86
  • 87
  • 88
  • 89
  • 90
  • 91
  • 92
  • 93
  • 94
  • 95
  • 96
  • 97
  • 98
  • 99
  • 100
  • 101
  • 102
  • 103
  • 104
  • 105
  • 106
  • 107
  • 108
  • 109
  • 110
  • 111
  • 112
  • 113
  • 114
  • 115
  • 116
  • 117
  • 118
  • 119
  • 120
  • 121
  • 122
46
C
HAPTER
4: U
SING
R
ESILIENCE
F
EATURES
■
Because Bridge A is the Root Bridge, it is also the Designated Bridge
for LAN segment 1. Port 1 on Bridge A is therefore selected as the
Designated Bridge Port for LAN Segment 1.
■
Port 1 of Bridges B, C, X and Y have been defined as Root Ports
because they are the nearest to the Root Bridge and therefore have
the most efficient path.
■
Bridges B and X offer the same Root Path Cost for LAN segment 2,
however, Bridge B has been selected as the Designated Bridge for the
segment because it has a lower Bridge Identifier. Port 2 on Bridge B is
therefore selected as the Designated Bridge Port for LAN Segment 2.
■
Bridge C has been selected as the Designated Bridge for LAN segment
3, because it offers the lowest Root Path Cost for LAN Segment 3:
■
the route through Bridges C and B costs 200 (C to B=100, B to
A=100)
■
the route through Bridges Y and B costs 300 (Y to B=200, B to
A=100).
Port 2 on Bridge C is therefore selected as the Designated Bridge Port
for LAN Segment 3.
STP Configurations
Figure 11
shows three possible STP configurations using SuperStack 3
Switch units.
■
Configuration 1 — Redundancy for Backbone Link
In this configuration, the Switches both have STP enabled and are
connected by two links. STP discovers a duplicate path and blocks one
of the links. If the enabled link breaks, the disabled link becomes
re-enabled, therefore maintaining connectivity.
■
Configuration 2 — Redundancy through Meshed Backbone
In this configuration, four Switch units are connected in a way that
creates multiple paths between each one. STP discovers the duplicate
paths and blocks two of the links. If an enabled link breaks, one of the
disabled links becomes re-enabled, therefore maintaining connectivity.
■
Configuration 3 — Redundancy for Cabling Error
In this configuration, a Switch has STP enabled and is accidentally
connected to a hub using two links. STP discovers a duplicate path
and blocks one of the links, therefore avoiding a loop.