Bridges Computer Networks Bridges Outline Repeaters Bridges Backward

Bridges Computer Networks

Bridges Outline Repeaters § Bridges § – Backward learning § Bridge Loops – Spanning trees (transparent bridges) – Source-routing bridges (e. g. , token rings) Computer Networks Bridges 2

Repeaters S 1 S 2 LAN 1 S 4 S 3 LAN 2 Repeater A repeater operates at the physical layer and forwards everything between the two LANs. LAN 1 and LAN 2 are in the same collision domain. Computer Networks Bridges 3

Bridges Bridge Leon-Garcia & Widjaja: Communication Networks Computer Networks Bridges 4

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. Computer Networks Bridges 5

Bridge Network Bridge LLC MAC MAC Physical A bridge is a store and forward device that separates collision domains. Computer Networks Bridges 6

Bridges S 1 S 2 S 3 LAN 1 port 1 B 1 LAN 2 port 2 S 5 S 4 port 1 Address Port B 2 Address LAN 3 port 2 Port Leon-Garcia & Widjaja: Communication Networks Computer Networks Bridges 7

Bridges S 1 S 2 S 3 S 5 S 4 S 5 LAN 1 port 1 B 1 Address S 1 LAN 2 port 2 Port 1 port 1 B 2 Address S 1 LAN 3 port 2 Port 1 Leon-Garcia & Widjaja: Communication Networks Computer Networks Bridges 8

Bridges S 1 S 2 S 3 LAN 1 port 1 Address S 1 S 3 S 2 LAN 2 B 1 port 2 S 5 S 4 B 2 port 1 Port 1 2 Address S 1 S 3 LAN 3 port 2 Port 1 1 Leon-Garcia & Widjaja: Communication Networks Computer Networks Bridges 9

Bridges S 1 S 2 S 3 S 4 LAN 1 port 1 Address Bridge 1 does not forward the frame to LAN 1 S 3 S 4 LAN 2 B 1 port 2 S 5 S 4 B 2 port 1 Port 1 2 2 Address S 1 S 3 S 4 S 3 LAN 3 port 2 Port 1 1 2 Leon-Garcia & Widjaja: Communication Networks Computer Networks Bridges 10

Bridges S 1 S 2 S 3 S 2 S 1 LAN 1 port 1 LAN 2 Bridge 1 Address Bridge 1 does not forward the frame to LAN 2 S 5 S 4 S 1 S 3 S 4 S 2 port 1 Port 1 2 2 1 LAN 3 Bridge 2 Address S 1 S 3 S 4 port 2 Port 1 1 2 Leon-Garcia & Widjaja: Communication Networks Computer Networks Bridges 11

MAN with Bridge Loops LAN 1 (1) B 1 B 2 (1) (2) LAN 2 B 3 (3) (2) (1) B 4 (2) LAN 3 (1) B 5 (2) Leon-Garcia & Widjaja: Communication Networks LAN 4 Computer Networks Bridges 12

MAN with Bridge Loops One solution to bridge loops Build a Spanning Tree! Leon-Garcia & Widjaja: Communication Networks Computer Networks Bridges 13

Bridges Summary Repeaters § Bridges § – Backward learning § Bridge Loops – Spanning trees (transparent bridges) – Source-routing bridges (e. g. , token rings) Computer Networks Bridges 14