Bridging, Switching, and Spanning Tree 149
Step 3
If the destination is a unicast and the address is not in the address
table, forward on all ports.
Step 4
If the destination is a unicast and the address is in the address
table, forward the frame out the associated port, unless the MAC
address is associated with the incoming port.
Consider Figure 4-8, which separates LANs with a switch.
Figure 4-8
Example Protocol Flows--Using a Switch
0200.3333.3333
Web
E0
E1
E2
DNS
DMAC = FFFF.FFFF.FFFF
SMAC = 0200.1111.1111
0200.1111.1111
E0
Address Table After Step 1
ARP (DNS)
0200.1111.1111
1
DMAC = 0200.1111.1111
SMAC = 0200.2222.2222
ARP
2
DMAC = 0200.2222.2222
SMAC = 0200.1111.1111
DNS Request
3
DMAC = 0200.1111.1111
SMAC = 0200.2222.2222
DNS Reply
4
DMAC = FFFF.FFFF.FFFF
SMAC = 0200.1111.1111
ARP (Web)
5
DMAC = 0200.1111.1111
SMAC = 0200.3333.3333
ARP
6
DMAC = 0200.3333.3333
SMAC = 0200.1111.1111
Connect to Web
7
0200.2222.2222
0200.1111.1111
E0
0200.2222.2222
E2
Address Table After Step 2
0200.1111.1111
E0
0200.2222.2222
E2
Address Table After Step 3
0200.1111.1111
E0
0200.2222.2222
E2
0200.3333.3333
E1
Address Table After Step 6
ch04.fm Page 149 Monday, March 20, 2000 5:02 PM