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Cisco 1721 router configuration

Hi all, Can anyone please assisst with configuration of a Cisco 1721 router. I need to set up two private LANs that are within 100 meter apart. Both these LANs are Class C and they have the same gateway address. The router has two interfaces (Ethernet 0 and FastEthernet 0) and must be configured with the following information:

LAN A - IP address: 172.16.0.110

            Mask: 255.255.255.0

            Gateway: 172.16.0.100

            DNS: 172.16.0.31

            Alternate DNS: 172.16.0.32

LAN B - IP address: 172.16.200.1

             Mask: 255.255.255.0

             Gateway: 172.16.0.100

             DNS: 172.16.200.2

For the internal addresses I must use 10.1.1.1 and 10.1.1.2 with a mask of 255.255.255.252.

Thank you in advance.

7 REPLIES
Cisco Employee

Re: Cisco 1721 router configuration

With a mask of 255.255.255.0, The gateway for LAN B is invalid.

Also, you are describing 3 LANs on a device with two LAN interfaces.

Are you routing?  NAT?  What is the topology?

Re: Cisco 1721 router configuration

Hi Phillip

Thanks for the reply, I am trying to use class c address with a NAT. There are two LANs at the moment. The network 192.168.0.0 and 192.168.200.0 with a mask of 255.255.255.0 on both LANs can be use to qualify for class c.

Bronze

Re: Cisco 1721 router configuration

Hi,

     You can use following config.

192.168.0.0 ---||RouterA||---10.11.1.1---<>----10.11.1.2---||RouterB||----192.168.200.0

RouterA:

#conf t

(config)#interface fastethernet0

(config-if)#ip addr 192.168.0.1 255.255.255.0

(config-if)#exit

(config)#interface fastethernet1

(config-if)#ip addr 10.11.1.1 255.255.255.252

(config-if)#exit

(config)#ip route 192.168.200.0 255.255.255.0 10.11.1.2

Side A client:

ip:192.168.0.x/24

gw: 192.168.0.1

RouterB:

#conf t

(config)#interface fastethernet0

(config-if)#ip addr 192.168.200.1 255.255.255.0

(config-if)#exit

(config)#interface fastethernet1

(config-if)#ip addr 10.11.1.2 255.255.255.252

(config-if)#exit

(config)#ip route 192.168.0.0 255.255.255.0 10.11.1.1

Side B client:

ip:192.168.200.x/24

gw: 192.168.200.1

Regards

Muammer

Re: Cisco 1721 router configuration

Hi Muammer

Thanks for the configs you've just brought me light. Is it possible to make use of one router to connect the two networks?, if so how can I do that?.

Thanks again in advance.

Cisco Employee

Re: Cisco 1721 router configuration

Are the two LANs on the same hub/switch, are are they on separate VLANs?

If they are sharing the same wire, you can just add a secondary address to the router interface, otehrwise you want to create a trunk to your switch the the multiple VLANs.

Re: Cisco 1721 router configuration

Hi  Phillip

The two LANs are on the seperate hub/switch (3 Comm) and no VLANs have been defined yet. The idea is to connect the two LANs with a copper cable.

Thank you.

Cisco Employee

Re: Cisco 1721 router configuration

There are two ways to do it:

- Make separate VLANs (best isolation)

- Use a secondary address

The fast fix is the secondary address:

interface fastethernet 0

ip address 172.16.0.100 255.255.255.0

ip address 172.16.200.100 255.255.255.0 secondary

interface fastethernet 1

ip address 10.1.1.1 255.255.255.252

ip address 10.1.1.2 255.255.255.252 secondary

Based on what you provided below, assuming that you meant "172.16.200.100" when you typed "172.16.0.100" and that 10.1.1.1 and 10.1.1.2 are the intended addresses of the roouter interface and not the destinations.  The data you have provided does not make complete sense.  You can just attach both switches to the fastethernet 0 interface.

(What you originally provided:)

LAN A - IP address: 172.16.0.110

            Mask: 255.255.255.0

            Gateway: 172.16.0.100

            DNS: 172.16.0.31

            Alternate DNS: 172.16.0.32

LAN B - IP address: 172.16.200.1

             Mask: 255.255.255.0

             Gateway: 172.16.0.100

             DNS: 172.16.200.2

For the internal addresses I must use 10.1.1.1 and 10.1.1.2 with a mask of 255.255.255.252.

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