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Need help big time making internet out of Comcast/AT&T

Hello,

I've been CCNA certified for 5 months.

Just got a CISCO891-K9 RT and trying to get WAN off ISPs like Comcast Xfinity / AT&T U-Verse.

These ISPs provide a modem+router equipment that does both WAN and wireless access point (DHCP as well).

I'm trying to feed one of LAN off of ISP routers to my CISCO router as a WAN.

I've been struggling past 3 hours trying to make this happens and deserves to be shot since I still can't figure it out.

Any help would be appreciated.

(So far, I've set VLAN tied to a DHCP. Also "ip nat out" on the port that gets feed from ISP router. etc etc).

1 ACCEPTED SOLUTION

Accepted Solutions
Purple

Need help big time making internet out of Comcast/AT&T

Hi,

No,you should never configure a default route with an outgoing interface if this interface is multipoint(like ethernet) but rather configure a default route with a next-hop which will be the ip address of the modem/router( the one you type in your browser to access the GUI of this modem/router). So if for example your modem/router IP is 192.168.1.1 then you should configure like this on Cisco: ip route 0.0.0.0 0.0.0.0 192.168.1.1

For NAT:

1)

-on LAN interface: ip nat inside

-on WAN interface: ip nat outside

2) create your NAT ACL, I suppose your LAN is 192.168.2.0/24

    access-list 1 permit 192.168.2.0 0.0.0.255

3) create your dynamic PAT

ip nat inside source list 1 interface x/x   where x/x is your WAN interface

Regards

Alain

Don't forget to rate helpful posts.

Don't forget to rate helpful posts.
6 REPLIES
Hall of Fame Super Gold

Re: Need help big time making internet out of Comcast/AT&T

  Post config.

New Member

Re: Need help big time making internet out of Comcast/AT&T

I'll post a config later today.

By the way, I am using U-Verse 3800HGV-B modem as a WAN bridge connection.

I have used other small routers to get WAN feed off of 3800HGV-B and worked fine.

But problme is when I plug in the Cisco router, 3800HGV-B configuraiton page indicates that the device not even picked up.

Does Cisco router invovle more manual config to get this? Or do I need that small router as another bridge in between?

Thanks.

Re: Need help big time making internet out of Comcast/AT&T

Setup One (Modem in bridge mode) : -

                                            20.30.40.5/30 ---> GW 20.30.40.1

LAN----------------------Cisco-----------------------Modem(Bridge)----------------------Internet

         192.168.1.0/24                                                                         

Cisco needs to have a default route to internet. NAT needs to be configured on cisco with LAN interface as nat inside and WAN as nat outside.

No special config will be required on modem as it will be a layer 2 bridge.

Setup Two (Modem acting as a router) : -

                                           .100                     .1                         20.30.40.5/30 ---> GW 20.30.40.1

LAN----------------------Cisco-----------------------Modem(Router)----------------------Internet

         192.168.1.0/24               10.0.0.0/24                                                          

Cisco can NAT 192.168.1.0/24 --> 10.0.0.100.  Cisco need default route with next-hop 10.0.0.1.

As modem is a router now - Modem will NAT 10.0.0.100 --> 20.30.40.5. Modem need a default route with nex-hop 20.30.40.1

In this very same setup if you do not NAT on the Cisco then you can NAT on Modem 192.168.1.0/24 --> 20.30.40.5. However in this case you need to add a route for 192.168.1.0/24 on modem with next hop 10.0.0.100

New Member

Re: Need help big time making internet out of Comcast/AT&T

I greatly appreciate your time and effort in creating this diagram and such.

If Cisco's WAN slot (Cisco's port-8) is connected to the Modem(Router)'s port-4, would it be then "ip route 0.0.0.0 0.0.0.0 it fa8"

Thanks.

Purple

Need help big time making internet out of Comcast/AT&T

Hi,

No,you should never configure a default route with an outgoing interface if this interface is multipoint(like ethernet) but rather configure a default route with a next-hop which will be the ip address of the modem/router( the one you type in your browser to access the GUI of this modem/router). So if for example your modem/router IP is 192.168.1.1 then you should configure like this on Cisco: ip route 0.0.0.0 0.0.0.0 192.168.1.1

For NAT:

1)

-on LAN interface: ip nat inside

-on WAN interface: ip nat outside

2) create your NAT ACL, I suppose your LAN is 192.168.2.0/24

    access-list 1 permit 192.168.2.0 0.0.0.255

3) create your dynamic PAT

ip nat inside source list 1 interface x/x   where x/x is your WAN interface

Regards

Alain

Don't forget to rate helpful posts.

Don't forget to rate helpful posts.
New Member

Re: Need help big time making internet out of Comcast/AT&T

Hello from my own Cisco Network!! Thanks for all the help ya'll!!!!

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