Bridges Advanced Computer Networks Bridges Outline Repeaters Bridges

Bridges Advanced Computer Networks

Bridges Outline Repeaters § Bridges § – Backward learning § Bridge Loops – Spanning trees Advanced Computer Networks Bridges 2

Repeaters S 1 S 2 LAN 1 S 4 S 3 Repeater LAN 2 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. Advanced Computer Networks Bridges 3

Bridges Bridge Leon-Garcia & Widjaja: Communication Networks Advanced 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. Advanced Computer Networks Bridges 5

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

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

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

Bridges S 1 S 2 S 3 S 4 LAN 1 Address Bridge 1 does not forward the frame to LAN 1 LAN 2 B 1 port 1 S 3 S 4 port 2 Port 1 2 2 S 5 S 4 B 2 port 1 Address S 1 S 3 S 4 S 3 LAN 3 port 2 Port 1 1 2 Leon-Garcia & Widjaja: Communication Networks Advanced 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 2 Port port 1 Bridge 2 Address 1 2 2 1 LAN 3 S 1 S 3 S 4 port 2 Port 1 1 2 Leon-Garcia & Widjaja: Communication Networks Advanced 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 Advanced Computer Networks Bridges 12

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