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Secondary IP Address

I need to understand how secondary ip address configure on router work when it is two different network


ip address 1xx.xx.7.2 secondary

ip address 1xx.xx.6.2



ip route 1xx.xx.6.0 FastEthernet0/1

ip route 1xx.xx.7.0 FastEthernet0/1

Now what should be the switch port configration for the port connected to FastEthernet 0/1 of the router. If i want keep two different network by mean of vlan ( say vlan 6 and vlan 7 ) how it will work ? How to set up the dhcp server and relay on the L3 router?


Re: Secondary IP Address

If your router interface with a primary IP subnet and a secondary IP subnet, then they must be on the same VLAN on your switch. In that case, there is no way to distinguish between the two subnets as far as DHCP is concerned, unless you want to do static mapping.

It sounds to me like what you really want to do is have two seperate VLANs and two seperate subinterfaces on your router. So, set up the router connection to the switch as a dot1q trunk, and make two seperate sub-interfaces on your router:

interface FastEth 0/1.6

 encapsulation dot1q 6

 ip address


interface FastEth 0/1.7

 encapsulation dot1q 7

 ip address

Then you can put your switch access ports on VLAN 6 or VLAN 7 as you want. Furthermore, the DHCP pools for the two VLANs will work independently.

Kevin Dorrell