Bridges
Networks: Bridges
1
S1
S2
S3
LAN1
S4
LAN2
Repeater
A repeater operates at the physical layer and forwards
everything between the two LANs.
LAN1 and LAN2 are in the same collision domain.
Networks: Bridges
2
S1
S2
S3
LAN1
Bridge
LAN2
S4
Copyright ©2000 The McGraw Hill Companies
S5
Leon-Garcia & Widjaja: Communication Networks
Networks: Bridges
S6
Figure 6.79
3
Bridges
• Operate at the data link layer.
• Bridges use backward learning in recording source
address on transmissions.
• Unlike repeaters, bridges will not forward a frame
onto another LAN segment if it knows about the
location of the destination node.
• Bridge management gets more complicated when
loops are possible in the frame route.
Networks: Bridges
4
Bridge
Network
Network
Bridge
LLC
LLC
MAC
MAC
MAC
MAC
Physical
Physical
Physical
Physical
A bridge is a store and forward device that separates collision domains.
Copyright ©2000 The McGraw Hill Companies
Leon-Garcia & Widjaja: Communication Networks
Networks: Bridges
Figure 6.80
5
S1
S2
S3
LAN1
LAN2
port 1
B1
Address
Copyright ©2000 The McGraw Hill Companies
port 2
S5
S4
LAN3
port 1
Port
B2
Address
Leon-Garcia & Widjaja: Communication Networks
Networks: Bridges
port 2
Port
Figure 6.81
6
S1
S1
S2
S3
S5
S4
S5
LAN1
LAN2
B1
port 1
Address
S1
Copyright ©2000 The McGraw Hill Companies
port 2
Port
1
LAN3
B2
port 1
Address
S1
Leon-Garcia & Widjaja: Communication Networks
Networks: Bridges
port 2
Port
1
Figure 6.82
7
S1
S2
S3
S3
LAN1
S2
LAN2
LAN3
B1
B2
port 1
port 2
port 1
port 2
Address
Port
Address
Port
S1
S3
1
2
S1
S3
1
1
Copyright ©2000 The McGraw Hill Companies
S5
S4
Leon-Garcia & Widjaja: Communication Networks
Networks: Bridges
Figure 6.83
8
S1
S2
S3
S4
LAN1
LAN2
B2
port 2
S1
S3
S4
Copyright ©2000 The McGraw Hill Companies
S3
LAN3
B1
port 1
Address
S5
S4
port 1
Port
1
2
2
port 2
Address
Port
S1
S3
S4
1
1
2
Leon-Garcia & Widjaja: Communication Networks
Networks: Bridges
Figure 6.84
9
S1
S2
S3
S2
S5
S4
S1
LAN1
LAN2
LAN3
Bridge1
Bridge 2
port 1
port 2
port 1
port 2
Address
Port
Address
Port
S1
S3
S4
S2
1
2
2
1
S1
S3
S4
1
1
2
Copyright ©2000 The McGraw Hill Companies
Leon-Garcia & Widjaja: Communication Networks
Networks: Bridges
Figure 6.85
10
MANs with Bridge Loops
LAN1
(1)
(1)
B1
B2
(1)
(2)
LAN2
(2)
B3
(3)
(2)
(1)
B4
(2)
LAN3
(1)
B5
(2)
Copyright ©2000 The McGraw Hill Companies
LAN4
Figure 6.86
Leon-Garcia & Widjaja: Communication Networks
Networks: Bridges
11
MANs with Bridge Loops
LAN1
D (1)
R (1)
B1
B2
R (1)
D (2)
(2)
B3
LAN2
Solution to bridge loops
(3)
D
D (2)
R (1)
Build a Spanning Tree!
B4
(2)
LAN3
R (1)
B5
(2)
LAN4
Copyright ©2000 The McGraw Hill Companies
Leon-Garcia & Widjaja: Communication Networks
Networks: Bridges
Figure 6.87
12