Running Cable Broadband with a cisco 1720 1

[bussche]

I am trying to setup my Cisco 1720 with 2 ethernet interfaces to connect to the internet via a Motorola Surfboard cable modem.
Basically the setup is I have Ethernet0 connected to my cable modem and FastEthernet0 running to the switch for the LAN. From what I remember I should just have to setup a static route so that any traffic coming from the lan is shot out to the Wan network, and any traffic coming from the Wan is shot back into the Lan network. I was doing some reading on the internet and I configure PAT as well to translate all the internal Lan ip’s to that external wan Ip.

From a host on the inside I can ping the routers internal 192.168.1.3 interface as well as the external 216.36.150.18 interface but not the 216.36.150.18 wan gateway.

Is there another step I’m missing? Here is my config:



User Access Verification
version 12.2
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname yr
!
enable secret (removed)
enable password (removed)
!
memory-size iomem 25
ip subnet-zero
!
!
!
!
interface Ethernet0
ip address 216.36.150.18 255.255.255.0
ip nat outside
half-duplex
!
interface FastEthernet0
ip address 192.168.1.3 255.255.255.0
ip nat inside
speed auto
half-duplex
no cdp enable
!
ip nat inside source list 1 interface Ethernet0 overload
ip classless
ip route 0.0.0.0 0.0.0.0 216.36.150.1
ip route 216.36.150.0 255.255.255.0 FastEthernet0
no ip http server
!
!
access-list 1 permit 192.168.1.0 0.0.0.255
dialer-list 1 protocol ip permit
dialer-list 1 protocol ipx permit
!
line con 0
line aux 0
line vty 0 4
password (removed)
login
!
end


Any Ideas? Thanks in advance, I appreciate any insight.

 

[IPKONFIG]

1) Did you setup the outside address with a DHCP that you got from the broadband provider or do you subscribe to get static IP addresses?

2) If you have DHCP from cable modem, change the IP address of the E0 interface to: ip address dhcp

3) Route statement for the 0.0.0.0 network should point to E0 instead of the IP address if you change to the DHCP option

4) Get rid of the IP route to 216.36.150.0 to the Fa0 interface, as it's not right. You don't need to point your internal routes to the inside unless you have multiple subnets besides what's configured on the router. I'm sure you have just the one.

"I can picture a world without war. A world without hate. A world without fear. And I can picture us attacking that world, because they'd never expect it."
- Jack Handey, Deep Thoughts

 

[bussche]

Yes we have a static Ip address from our provider.

 

[bussche]

4) Get rid of the IP route to 216.36.150.0 to the Fa0 interface, as it's not right. You don't need to point your internal routes to the inside unless you have multiple subnets besides what's configured on the router. I'm sure you have just the one. "

Do you mean I don't need to point external traffic to the internal network?

 

[burtsbees]

Your modem does not appear to be in bridge mode---it may be NATting...

Burt

 

[IPKONFIG]

Routers know about all directly connected interfaces by default, so you don't need that route in the router. If you had other subnets behind your router you'd need to advertise those. Such as 172.16.x.x or 10.x.x.x

Also, Burtsbees points out another good point. You're cable modem could be doing the NAT for you and not bridging this could cause you issues as well.


"I can picture a world without war. A world without hate. A world without fear. And I can picture us attacking that world, because they'd never expect it."
- Jack Handey, Deep Thoughts

 

[bussche]

I am running it through a Motorola SB5101 cable modem, which does not NAT I believe.

 

[IPKONFIG]

interface Ethernet0
ip address 216.36.150.18 255.255.255.0
ip nat outside
half-duplex <--change this if it will support full duplex
!
interface FastEthernet0
ip address 192.168.1.3 255.255.255.0
ip nat inside
speed auto
half-duplex <--change this as well for full duplex
no cdp enable
!
ip nat inside source list 1 interface Ethernet0 overload
ip classless
ip route 0.0.0.0 0.0.0.0 216.36.150.1 <--address of modem, then this is good
ip route 216.36.150.0 255.255.255.0 FastEthernet0 <--Delete this as you don't need it
no ip http server
!
!
access-list 1 permit 192.168.1.0 0.0.0.255 <--If this is the subnet that is sourcing all the traffic then your PAT should work, if you want to make sure you can use this:

access-list 1 permit 0.0.0.0 0.0.0.0


You're configuration is spot on for PAT overload


"I can picture a world without war. A world without hate. A world without fear. And I can picture us attacking that world, because they'd never expect it."
- Jack Handey, Deep Thoughts

 

[bussche]

216.36.150.1 is the address of the gateway that the modem connects to, 216.36.150.18 is the modems address, so I should change it that then?

 

[IPKONFIG]

Yes, always the next hop address should be used.

"I can picture a world without war. A world without hate. A world without fear. And I can picture us attacking that world, because they'd never expect it."
- Jack Handey, Deep Thoughts

 

[bussche]

Thats what I though, if I have my Ethernet0 interface configured with "216.36.150.18" then wouldn't the next hop be the gateway of 216.36.150.1?

 

[IPKONFIG]

If your router is .18 and the connection between the router and the cable modem is L3 and the modem (which should be the gateway) is .1 then that's where you point it. Remember that by default routers know about all directly connected networks. If you want to go outside of what the routers knows, you have to tell it how to do it. So if you want something outside of the two addresses that it knows about, then these routes must be entered into the router as static routes.

i.e. ip route 10.0.0.1 255.0.0.0 FastEthernet 0

That would point that RFC 1918 address to the inside of your network. I'd suggest to keep things simple you do this:

ip route 0.0.0.0 0.0.0.0 ethernet 0

The only difference (which shouldn't affect you) is that it will show as a directly connected route instead of having an AD of 1. (Big whoop in this situation) Won't affect you.

"I can picture a world without war. A world without hate. A world without fear. And I can picture us attacking that world, because they'd never expect it."
- Jack Handey, Deep Thoughts

 

[IPKONFIG]

Oh, also if .18 is the modems address, you can't use it as your outside interface i.e. Ethernet 0

What static IP range did your broadband provider give you? Give me this and we'll get this working.

"I can picture a world without war. A world without hate. A world without fear. And I can picture us attacking that world, because they'd never expect it."
- Jack Handey, Deep Thoughts

 

[bussche]

216.36.150.18 is the static IP we were assigned by our ISP.

 

[IPKONFIG]

Yes, but what was the mask? /24, /29 This is important to make this work.

"I can picture a world without war. A world without hate. A world without fear. And I can picture us attacking that world, because they'd never expect it."
- Jack Handey, Deep Thoughts

 

[bussche]

oh sorry I mistunderstood you, it is 255.255.255.0

 

[IPKONFIG]

Ok, so you have a /24, if the modem is .18, then your router can be anything from .1 -.254 excluding the modems address.

If they told you the Gateway was .18, then I'd change the IP address of E0 to anything but .18, if they said the Gateway is .1, then you shouldn't have to make a change.

Ping the Gateway from the router..does it work?

"I can picture a world without war. A world without hate. A world without fear. And I can picture us attacking that world, because they'd never expect it."
- Jack Handey, Deep Thoughts

 

[bussche]

Okay so if im understanding you correctly the in the 216.36.150.0 /24 network, the gateway at the isp's end will have a ip address (obviously) but the modem as well as the ethernet interface on my router will both hav they're own ips? I thought that the modem just modulated the signal to go over the cable lines?

 

[IPKONFIG]

You are correct. If the Gateway is not the modem then it shouldn't have an IP address. It should be a layer 2 device that bridges the traffic between your router and the gateway. Only layer 3 devices will have IP addresses. If you have the order from the broadband company all the addressing information should be listed. DNS, Static IP range, Gateway and Subnet information. You're router must be on the same subnet as the Gateway. And your static route should point to that Gateway out of the E0 interface.

"I can picture a world without war. A world without hate. A world without fear. And I can picture us attacking that world, because they'd never expect it."
- Jack Handey, Deep Thoughts

 

[bussche]

Okay so based on what you've just confirmed, shouldn't the E0 interface ben the .18 address, and the next hop for the staic route will be the .1 gateway address?