251
FIGURE 11.11 Inter-VLAN example 3
Since the hosts don’t list a subnet mask, you have to look for the number of hosts used in each VLAN to figure out the block size. VLAN 1 has 85 hosts and VLAN 2 has 115 hosts. Each of these will fit in a block size of 128, which is a /25 mask, or 255.255.255.128. You should know by now that the subnets are 0 and 128; the 0 subnet (VLAN 1) has a host range of 1–126, and the 128 subnet (VLAN 2) has a range of 129–254. You can almost be fooled since HostA has an IP address of 126, which makes it almost seem that HostA and B are in the same subnet. But they’re not, and you’re way too smart by now to be fooled by this one!
Here is the switch configuration: 2960#config t 2960(config)#int f0/1 2960(config-if)#switchport mode trunk 2960(config-if)#int f0/2 2960(config-if)#switchport access vlan 1 2960(config-if)#int f0/3 2960(config-if)#switchport access vlan 2
Here is the router configuration: ISR#config t ISR(config)#int f0/0 ISR(config-if)#no ip address ISR(config-if)#no shutdown