Routing Question

[sjasmund]

Hello,

I need some direction in integrating a Cisco 1720 router for a T1 line into an existing network. I should say that I'm primarily a programmer but I do some (more lately) networking for my clients. I'm comfortable doing easier stuff but routing is a little over my head.

The company has an existing network, which utilizes static IP addresses that we cannot change. These addresses are 10.241.145.xxx/255.255.255.0

A T1 line was installed to use on the network and we would like to integrate it into the existing network. The router that was supplied for the T1 line is a Cisco 1720 with an IP address of 68.22.0.161/255.255.255.224. Available IP's for the router do not match (either IP or subnet) what we need in the existing network.

Using my notebook to test, if I configure it with an IP in the valid range for the router (68.22.0.162), I have no problems. Using an IP from the existing network obviously doesn't work since it's not withing the available range.

I plugged in an extra Linksys router I have and I could configure the WAN side of it but ran into problems since it only recognizes IP's within a specific range (192.168.1.x)on the LAN side. It's my understanding from the T1 provider that we cannot make changes to the Cisco router.

Can someone please give me a direction to go? I think I need a better router than the Linksys that will allow me to configure both the WAN side and the IP range for the LAN side. However, at this point, I'm just guessing.

Thanks,
Scott

 

[ccie9545]

If you cannot configure the WAN and LAN side of the Linksys router, then you might have some difficulty. However, I would be surprised if you cannot configure these on the Linksys.

Most lower end routers that are similar to the Linksys come with Network Address Translation built in to the default configuration. NAT allows a private IP address to be translated into a public IP address. Normally, you would only have to configure the WAN side of the Linksys with a valid IP address that was given to you by the provider. Similar to what you did on the laptop. Then you would have to configure the LAN side with an address that is within the range of hte company network (10.241.145.0/24). Then set all of the computers on the network to have there default gateway IP address to be that of the Linksys.

This is assuming that you can change the IP addressing on the Linksys. If you cannot, you will have to look into another device. If you have to look into another device, let me know how much money you are willing to invest and I can make a suggestion. There are many relatively inexpensive solutions for these situations.

Erik Rudnick, CCIE No. 9545
mailto:erik@kuriosity.com

 

[sjasmund]

Erik... thanks for the reply. The Linksys router is a BEFSR41. I'll look and see if it has NAT as part of the config.

If not, please feel free to suggest alternatives in several price ranges < $1000.

Thanks,
Scott

 

[ccie9545]

It looks like it does have NAT. What you are going to probably have to do is connect via a web browser. Most of these home/small office routers have a web browser interface for configuration. If you set a PC to DHCP (receive IP addressing information dynamically) the router will most likely have a default setting that will assign an address.

In fact, if I remember correctly the default for the linksys is 192.168.254.254 is the default address, that is racking the brain though...not really sure if that is right.

But you should be able to find the default settings in the documentation. Once you find default address, just type this in the web broswer of the pc that you connected to the router:

http://192.168.254.254

or whatever is the address of the router. that should give you a prompt for a logon. documentation should have default login information.

There should be a WAN page, where you configure the WAN settings, a LAN page where you configure the LAN settings, and a NAT page if you would like to give any outside access to an internal box.

here is the link to the documentation.

http://www.linksys.com/products/product.asp?prid=20&grid=23

i didn't have time to look at it. but if you have questions don't hesitate to ask.....

Erik Rudnick, CCIE No. 9545
mailto:erik@kuriosity.com

 

[sjasmund]

Erik,

I have no problem getting into the setup for the Linksys router (FWIW, the IP is 192.168.1.1) but there are no references to NAT within the configuration screens.

I follow what you've described needs to happen... there is a &quot;Dynamic Routing&quot; and a &quot;Static Routing&quot; tab within the setup but I'm not sure what to set up here.

The &quot;Dynamic Routing&quot; tab shows Working Mode (Gateway or Router), TX (Disabled, RIP1, RIP1-Compatible and RIP2)and RX (Disabled, RIP1, RIP2).

The &quot;Static Routing&quot; tab shows a Route #, Destination LAN IP, Subnet mask, Default Gateway, Hop Count, and Interface (LAN or WAN).

Thanks,
Scott

 

[ccie2bee]

It can be done with the Links it just needs extra work. You need DHCP disabled, static enabled, asign IPs.

Linksys FAQ > step by step

http://kb.linksys.com/cgi-bin/om_is...ev.nfo&record={406}&softpage=IKW_ENU_JDocView

hope this helps

 

[sjasmund]

I've already done that... I changed the Linksys LAN IP to one that is friendly on the network. I set the WAN IP to one that is acceptable by the router.

On my notebook, if I use an IP from the range that the Cisco router will allow, everything works fine. However, if I change the IP on my notebook to one that will be used in the LAN, I'm dead. I can still ping the Linksys router as well as the Cisco... I just can't get anything on the Internet.

Scott

 

[ccie9545]

did you change the default gateway on the computer as well? (just to make sure).

If there is a utility on the linksys that allows you to ping, you might want to try pinging the cisco router from the linksys. if this works, try pinging past the cisco router to the internet. if this doesn't work make sure that you have a default gateway set up on the linksys router. The default gateway should point to the IP address of the cisco router.

After looking at the manual for the linksys it looks like the forwarding section is actually the section that configures NAT. You might also want to check the filtering section and make sure that there are not any filters that would be blocking your access.

Let me know the status..... Erik Rudnick, CCIE No. 9545
mailto:erik@kuriosity.com

 

[matt95gsr]

DNS. Did you configure DNS server addresses on your laptop or on the computers in the network? If not, you need to get DNS server addresses from your ISP and configure your PC's accordingly.

 

[ccie2bee]

Links wan set to 68.22.0.161/255.255.255.224
Disable DHCP
NAT is automatic
Static routing <on Links>
Assign ip and mask >> hop if going to another router
Gatway will be 192.168.1.1 for each route you create 10.241.x.x
<<this will need to be asigned on Pc's as well>>
Under port forwarding Disable Wan request this will solve the pinging.
Also you will need to open some ports for the apps you are running.>> ie 80 http 21 ftp 23 telnet etc
Assign ip for all pc and gateway.

Links router will allow up to 20 routes.

Hope this helps

 

[sjasmund]

Hi guys... thanks for all the tips. I've tried many of the suggestions here without success.

I'm beginning to wonder if there is a problem with the router. I picked up a couple replacement routers and will be heading back out to the client today with another set of eyes to look at it with me.

Thanks,
Scott

 

[sjasmund]

Thanks again guys... it was the router. I plugged in a different one and it was plug-n-play!

Thanks,
Scott