Point-to-Point T3

Unanswered Question
Mar 17th, 2010


I am looking to setup a point-to-point T3 connection between our Cisco 2821 and Cisco 3640 routers using the internal NM-1T3/E3 cards. I have the cards installed and the controller has been loaded. However, I am not too familiar with configuring T1 or T3 connections. Despite assigning the IP addresses on each interface and having them advertised using EIGRP, are there any other steps I need to take? The current connection between these two devices are two T1 connections that are load-balanced. My plan was to simply assign the IPs on the T3 serial interface, make sure the networks are advertised via EIGRP, and then shut off the T1 connections. Is there anything more I am missing or need to configure?

Thank you!

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Collin Clark Thu, 03/18/2010 - 06:45

Your plan should work. Here's an example of a T3 configuration-

interface Serial1/0
ip address
load-interval 30
dsu bandwidth 44210
serial restart-delay 0

dsu bandwisth 44210 is critical. This speed must match your carriers configured speed exactly. Other than that the above configuration should work (in the US).

Hope it helps.

ngeorge06 Thu, 03/25/2010 - 07:57

Thanks. I forgot to ask about framing, as I think that is the piece I missed. The equipment from the telco provider displays the CUST end can handle c-bit or m13. However the routers only show c-bit or m23 support. I'm assuming c-bit is the route to go based on my other research but I wanted to clarify. The telco network appears to be using m13.

ngeorge06 Thu, 03/25/2010 - 08:18

Thanks. Even though I cannot bring up the other side of the connection, will I be able to see "up" status if the one side is configured and connected properly? I have configured an ip, set c-bit framing, clock source internal, and bandwidth, but still seeing down/down.

Collin Clark Thu, 03/25/2010 - 08:23

You should be seeing up/down. down/down usually means there is a physical layer problem. Are you getting a green light on the card? What are the LEDs on the smart jack reading? How far is the extension? You can do a physical loop on the extension to verify it is working along with the carrier network.

ngeorge06 Thu, 03/25/2010 - 08:37

I am seeing down/down. From the smark jack, the CUST portion is reading green for c-bit. Network portion is reading AIS and M13, with a green status. I know that when I was experimenting with the cisco config previously I got to up/down, but I restarted the router without saving config on purpose to make sure I could document the settings to bring the other side up this evening and begin using the connection.

ngeorge06 Thu, 03/25/2010 - 08:42

I also forgot- on the router:

EN is green
AL is amber

AIS is amber

CD is green

Thank you for helping me troubleshoot!

Paolo Bevilacqua Thu, 03/25/2010 - 13:03

Be aware that while the 2821 is probably ok, the 3640 will melt much before you get close to full circuit utilization.

ngeorge06 Fri, 03/26/2010 - 07:23

I am aware that both routers will only run as a subrate T3; right now I just need to get the connection up and in the near future I should be able to upgrade routers. My managers are aware that we are not expecting full-line speed.


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