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Can a router use one IP address for more than one Interface?

Chris Snape
Level 1
Level 1

Hi People,

Basically I need a router to 'pass through' traffic without it changing the ip subnet. I have live IP addresses behind the router, attached to fa0, and they have the same ip range/subnet as the routers atm0 interface (I purchased a Non-NAT setup from my ISP).

My question is how to setup the router interfaces so they use the same IP address for the ATM interface and the Ethernet interface?

On standard consumer products you can simply turn off the NAT and it disables the LAN setup allowing live IPs behind the router.

I am using a /29 setup so have 6 ips. Everything I have looked at shows the usage of NAT but I guess I don't need that.

If I try to ping the IP behind the router from the command prompt it gets stuck in a loop between itself and my ISPs gateway.

Is that because of this - ip route 0.0.0.0 0.0.0.0 dialer 0 ??? I guess so but what is the alternative?

Oh, I am using an SR520 series router with an ADSL over POTS Wan link.

Regards,

Chris Snape (UK)

1 Accepted Solution

Accepted Solutions

Mlman1965
Level 1
Level 1

I thought I had a solution for you, but didn't look at the capabilities of the router first.

It is possible in the entreprise series routers (72XX, 76XX, 65XX), but I don't think the SR520 will support it.

I recently did a BGP exercise where we assigned a router IP adress to a loopback & then configured the ports to use the loopback.

Ex:

interface Loopback0

ip address XX.XX.XX.XX 255.255.255.248

interface ATMY/Y

ip unnumbered loopback0

interface FastEthernetZZ

ip unnumbered loopback0

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