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I am configuring a router to three different subnet as follow.




In my cisco router I am doing the following.


(config-if)# ip address

This works. However, when i go to configure my fa1/0. i got the following.

(config-if)# ip address
% overlaps with FastEthernet0/0

How do i resolve this problem?

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up vote 4 down vote accepted

The router is correct, because with that subnet mask those addresses do overlap., which is what your command tries to configure, is part of a subnet that includes everything from through What you mean to configure is which is a mask of

You may find it useful to use a subnet calculator (ex: or on my Linux workstations I use the "sipcalc" package).

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You have a /21 mask (

The first interface ( is then in this subnet:

Address:          11000000.10101000.00000 001.00000001
Netmask: = 21   11111111.11111111.11111 000.00000000
Wildcard:            00000000.00000000.00000 111.11111111

Network:       11000000.10101000.00000 000.00000000
HostMin:          11000000.10101000.00000 000.00000001
HostMax:        11000000.10101000.00000 111.11111110
Broadcast:        11000000.10101000.00000 111.11111111

As can be seen from above, this network includes* the 192.168.2.x range, so the IP on the second interface, is already within the range on the first interface.

If you need only IPs, consider using /24 mask, or use for the second interface, and for the third.

*actually goes from to

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