Simple Ethernet to Ethernet setup (cisco 1605R) But I can't get it to work.

I am trying to replace a netgear router which has a very simple setup with a cisco 1605 router. (I have to reboot the netgear every day)

My setup with netgear (Which works): Cable coming in from Time Warner connects to Time Warners router LAN port from the Time Warner Router connected to WAN port on netgear LAN port on netgear connected to my hub.

IP of netgear router: XX.XX.XX.54 subnet Gateway:xx.xx.xx.53 (This is the cable router) LAN IP of netgear router

I bought a 1605 because it has 2 ethernet ports so my plan was have Ethernet0 connect to my LAN and Ethernet1 connect to the Internet.

under config of Ethernet0 I tried to add: ip address xx.xx.xx.54 secondary and get the error: ip address xx.xx.xx.54 xx.xx.xx.52 overlaps with Ethernet1

If I change the subnet to I get the error: ip address xx.xx.xx.54 Bad mask /31 for address xx.xx.xx.54

I only have on static ip address: xx.xx.xx.54, the xx.xx.xx.53 is Time warners cable modem.

Does any one have any ideas of what I should try? The key to me is that it does not like xx.xx.xx.52 which is NOT one of the numbers I typed in. So it must have something to do with the subnet mask. But I don't know what. I took most of this from a working T1 (1601R) and substituted Ethernet1 for Serial0.

Thanks in advance, Rob

hostname cisco1605 ! ip subnet-zero no ip finger ! interface Ethernet0 description connected to LAN ip address ip nat inside ! interface Ethernet1 description connected to Internet ip address xx.xx.xx.53 ip nat outside ! router rip version 2 passive-interface Ethernet1 network no auto-summary ! ip classless ip route Ethernet1 no ip http server ! ! line con 0 transport input none line vty 0 4 login ! end

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Why are you creating a secondary interface? Are you using a real public IP or is this a private IP address on the outside interface?

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Networking is not what I do for a living (I am one of the programmers here) So I am not sure what you are asking.

I want the router to have both a static public IP address that can be accessed by the outside world, and an inside ( number for us inside. Once I get this working I will add port forwarding to send any thing that comes in on port 25 to our mail server, and anything on 1433 to our MS-SQL server.

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Not really. Try entering the IP address on the outside interface but do NOT put seconadary on the end of it and make sure that the /30 range that you are configuring is not part of any network on any other interface.

interface eth0 ip address x.x.x.53 no shut ! ip route x.x.x.54


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You don't want to do this. Each interface gets one address, you will then use NAT to translate from the 192.168.x.x network to your real IP address. The 52 is refering to the network address.

xx.xx.xx.52 - Network address xx.xx.xx.53 - Host 1 xx.xx.xx.54 - Host 2 xx.xx.xx.55 - Broadcast address is a network that cannot have any hosts. It would only have a network address and a broadcast address, pretty useless.

xx.xx.xx.54 - Network address xx.xx.xx.55 - Broadcast address

No room for hosts there...

What you have in the config portion is close. You need to define NAT next. First you will need to define which hosts or networks will be allowed to be NATed with an access-list. something like this...

router(config)#access-list 5 permit router(config)#access-list 5 permit

...assuming you are using the old classfull networks, which you may or may not be since you are using RIPv2 which allows for variable length subnet masks (VLSM). If you are using VLSM you will need to look into wildcard masks in access-lists.

After you define who can be NATed, you need to setup the NAT.

router(config)#ip nat inside source list 1 interface e0 overload

If I remember right, that should do it.

One word of advice though...a 1605 isn't exactly the fastest router on earth. If I were you I would go with a PIX 501 or 506e. It's more secure and it's tons faster. The config is a bear if you don't have PIX experience, but there is a GUI that is somewhat helpful. There are also other SOHO class firewalls out there that will do a better job than a 1600 series router.

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Thanks for you help,

I kept the Ethernet1 (outside) as:

interface Ethernet1 description connected to Internet ip address ip nat outside

Is that correct?

I still get: ip address overlaps with Ethernet0

You did mean 54 for E0, right? (i tried it both ways)

I didn't get this far because the E0 failure above.

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Thanks for you help,

Close but I am still confused as what to do. What would seem right to me is: interface Ethernet0 ip address ! interface Ethernet1 ip address ! But I can not enter this because of the error message: ip address overlaps with Ethernet1

What specifically should I put in E0 and E1?

I guess I was planning to get the NAT working after I could at least get connected to the Internet.

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Gah! Why are you putting the same network on both Eth0 and Eth1 interfaces. I thought that you said that the Cisco is just replacing the Netgear and connecting to the Time Warner router?

"IP of netgear router: XX.XX.XX.54 subnet Gateway:xx.xx.xx.53 (This is the cable router)"

So, you have ---- --- LAN. Yes?

The Time Warner router will have /30 on it's interface that connects to the Cisco and the Cisco Eth1 will have /30. Eth0 will then have an RFC1918 address range such as /24 or something similar. What you are trying to do is configure two interfaces with the same IP range,

"Close but I am still confused as what to do. What would seem right to me is:

No! If your Time Warner router has then you can't also configure it on the Cisco. You should have;

< Time Warner - /30> ----< /30 - Cisco - /24> --- LAN

! interface eth1 ip address ip nat outside ! interface eth0 ip address ip nat inside ! # set up NAT for the LAN clients ip nat inside source list 120 pool NAT-POOL overload ip nat pool NAT-POOL netmask ! # match traffic that is to be NATed access-list 120 permit ip any ! # send all traffic destined for the outside to the Time Warner router ip route


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You have to get NAT working BEFORE you can connect to the internet. That's pretty much all the Netgear box was doing.

Eth1 and Eth0 MUST be on different networks. That's what a router does, connects networks together. mask for one interface, xx.xx.xx.54 mask for the other. make sure IP routing is enabled. Configure NAT. Set the static default route (redistribute into RIP if you need to) and have a blast.

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