Test lab question

On a 2801, we have one ethernet interface that will serve as a gateway for internet access for the rest of our network that has a 255.255.255.240 mask. The other ethernet interface connects to the "public" network where we will gain internet access that has a 255.255.240.0 mask.

We can ping both interfaces from the console port, but cannot pass traffic between the two ethernet interfaces.

Is there a NAT/PAT command that we are missing somewhere? Perhaps we are overlooking something else?

Your thoughts and suggestions please.

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EdTheLad

Your question is too vague, i suggest you post the running-configs!

Judd

If I want to pass traffic between two different networks with two different masks, will I need to configure NAT or PAT on the 2801 to do so? If so, could someone please get me started on the proper commands? It would be a similar setup to a standard perimeter router that connects a public network to a private network.

If this isn't enough info, I can post the configs but it will be next Monday before I can do so.

EdTheLad

A router doesnt need any special config to route between to different networks with different masks.The length of the mask is only an issue if your using classful routing protocols like RIPv1 and IGRP.Do you have dynamic routing setup? have u configured static routes? Have you been asigned a public IP address? NAT is used to translate your private source IP address to a public source IP address, do you need to do this?

Judd

We are using static routes. We are using a static address from the "public" network and have configured a static address for the "private" interface as well. Both addresses are using the reserved 172.16 network. The "public" network providing the internet is a 172.16.160.x address with a 255.255.240.0 mask and our private network is a 172.16.173.x address with a 255.255.255.240 mask.

We can't get internet to pass between the two interfaces and are wondering if it's a command that we were missing or if it's possibly a NAT or PAT issue. My first guess was NAT but as you mentioned that's only necessary to translate private addresses to public addresses.

Any other thoughts without seeing the configs?

EdTheLad

Judd wrote:

We are using static routes. We are using a static address from the "public" network and have configured a static address for the "private" interface as well. Both addresses are using the reserved 172.16 network. The "public" network providing the internet is a 172.16.160.x address with a 255.255.240.0 mask and our private network is a 172.16.173.x address with a 255.255.255.240 mask.

We can't get internet to pass between the two interfaces and are wondering if it's a command that we were missing or if it's possibly a NAT or PAT issue. My first guess was NAT but as you mentioned that's only necessary to translate private addresses to public addresses.

Any other thoughts without seeing the configs?

A picure would be a help because im still a little confused with your setup.
"The public network providing the internet is a 172.16.160.x address with a 255.255.240.0 mask".Is this an ISP or has this address range been assigned to your company bye an ISP?Im assuming this address range has been assigned to you because you are using a subnet of it for your private addressing.
Can you ping your ISPs gateway ?
Is the 172.16.173.x/28 network configured on the gateway router or are there other routers in between ?

Humper

I am lost with this question Judd, you are going to have to explain alot better, show us a picture or configs!

Judd

I'm sorry guys; I'll post the configs next week if we can't figure it out. It's somewhat difficult to explain I guess.

Basically, we have a private network within another private network that we wish to give internet access to. Visualize 3 rings with the outermost ring being the ISP, the middle ring being the "host" network-which has internet access already, and the inner ring being our little private network that we want to give internet access to but cannot because we can't get the two ethernet interfaces that connect the middle ring and inner ring to pass traffic.

It's physical connections are: middle ring switch > inner ring router e0/0 > inner ring router e0/1 > inner ring switch

Anything?

EdTheLad

The only thing i can you you can have a problem with at the moment is your routing between the middle ring and inner ring.The ISP will have a route to your 172.16.160.x/20 network as internet is currently working.Since your address 172.16.173.x/28 is a portion of 172.16.160.x/20 the ISP will also be able to reach your inner ring if your internal routing is correct.On your
gateway router to the ISP are there routes for the 172.16.173.x ?
Use the "show ip route" to check routes to and from the internet for network 172.16.173.x for all routers involved.

Judd

ed_the_lad wrote:

On your
gateway router to the ISP are there routes for the 172.16.173.x ?

Since we are a little network within a bigger network, we don't have access to the internet router. We are essentially trying to "plug" a Cisco 2801 into a switch on the middle ring so that we can provide access to the internet for the inner ring. We have been given a static address for the router interface that faces the middle ring, and we have statically assigned an address to the other router interface for the inner ring.

This seems simple enough but we can't figure out why we aren't getting internet. Hopefully we aren't having a colossal brain fart, but it's beginning to look that way...