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I have a Cisco 2620xm router that I have ran into trouble getting it to connect to a comcast modem/gateway for internet service. The router and modem used by Comcast is a DPC3... The interfaces on the Cisco router are Aux, Console, Fast Ethernet 0/0, Ethernet 0 (Which shows in the terminal as Ethernet 1/0 and has a Serial )/0 port right next to it, looks group with it on the router), and at T1 WIC (CSU/DSU).

Does this require me to have another additional WIC card? Or can I use the Ethernet 1/0 port to connect the Comcast modem into? If I can't use either of the Ethernet ports to connect to a modem, would the T1 card be fine to use for regular Comcast high speed internet?

What I am trying to achieve here is a Cisco 2600xm router that will get its internet from a Comcast modem/router, then there will be a switch that will connect to the Cisco router to service other computers/servers in the network.

I would prefer for the Cisco 2620xm to grab its information/IP address using DHCP from the Comcast modem/router. I think I may need to upgrade the IOS on the router, but not sure how to get the upgrade onto the router.

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    Get a new router. The 2620XM has been end of life since 2012, end of sale since 2007. It was designed in an era where T1's were considered high speed links; it wasn't designed to provide the performance necessary for today's networking. Per Cisco documentation, the forwarding rate of this platform is just over 15Mbps with no advanced features enabled. Your Comcast Internet link probably easily exceeds this device's capability to handle traffic. – YLearn Jun 6 '15 at 5:31
  • @YLearn: The internet works just fine actually. I think I have a duplex problem however (as I get an orange light instead of a green light on the modem). What rack mountable routers do you recommend for use with my comcast modem? Also, what did you mean by advanced features? – Kevin Jul 29 '15 at 22:11
  • From the referenced link: As you add ACL's, encryption, compression, etc - performance will decline significantly from the given numbers, unless it is a hardware-assisted platform, such as the ASR 1000, 7600 or 12000, which process QoS, ACL's, and other features in hardware (or when a hardware assist is installed, for instance an AIM-VPN in a 3745 will offload the encryption from the CPU). I would have to check the specific platform, but this may also include routing protocols, NAT, the DHCP service, NTP, and many other features. – YLearn Jul 29 '15 at 22:34
  • Sure, you can get online, but it's going to be slooooooowwwwww....... – Michael Hampton Jul 29 '15 at 23:43
  • @MichaelHampton: Do you know of any Cisco rack mountable routers that perform at Gigabit speeds, or speeds best compatible with Comcast High Speed Internet? – Kevin Jul 31 '15 at 16:28
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Or instead of a static route you could have setup a default route via this command

Ip route 0.0.0.0 (interface)

which is stating that if you want to reach any network outside of the LAN go through this interface, you may also want to setup ipv6 routing via this command First you must enable ipv6 forwarding

Ipv6 unicast-routing

Then

IPv6 route ::/0 (interface)

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I figured out the issue. I found that the T1 Card was operational, but as YLearn explained it wasn't for use with Comcast High Speed Internet.As for the dhcp command, I upgraded the IOS via TFTP which allowed me to use the command. I was however able to use a static IP address given to me by Comcast in the configuration.

I found that the ip route settings needed to point to the gateway of my ISP (ex. ip route 0.0.0.0 0.0.0.0 COMCAST GATEWAY IP ADDRESS). I put the ip address handed out by Comcast instead of its gateway the whole time.

Once I did this successful step, I was able to ping out to google.com, facebook.com, etc successfully.

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