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1394
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18
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18
Replies

Easy question! 1841 Router

shelly_ratliff
Level 1
Level 1

I don't know ANYTHING about routers and my boss wants to know why we have what looks to be 2 T1 lines going into the 1841 router and only 1 network cable coming out to the network. I don't have a clue but am thinking maybe its a redundancy thing?

I have attached a couple of pictures showing the router and cables.

The red cable is plugged into the port labeled FE 0/0 and the other end of it goes into my network hub/switch.

The blue cables are plugged into slots 0 and 1 which are labeled T1 DSU/CSU. The other end of those cables are plugged into T1 lines.

He wants to know why we can't just get rid of one of the T1 lines!

18 Replies 18

Jon Marshall
Hall of Fame
Hall of Fame

Could you post the config of the router - it could well be that both T1's are in use.

Do you know how to obtain config of router ?

If not do you know an IP address of the router you can telnet into

OR

do you have a laptop with a COM port and one of the Cisco blue rollover cables ?

Jon

Jon,

I don't know how to obtain the configuration of a Cisco router. I don't know the ip address and it is not on the same network segment as my desktop computer. I will have to bring in my laptop tomorrow. I have the blue rollover cable which you describe. I don't know any passwords to this router. Am I going to be able to at least display the configuration or copy it?

Shelly

We can talk you through connecting up to the router but if you don't know the passwords then apart from trying the obvious such as "cisco" or any or passwords you may use internally the only way to get access to the running config would be to do a password recovery. This does a reload of the router so there would be an outage.

Jon

I located a printout of the configuration.

It is described as DS1 3Meg Managed ISP via multi-t1.

Without retyping the entire configuration, the things that stand out to me are as follows:

Interface Multilink1

description : MDG: 3M: S3/0/0/23:0 ....

no cdp enable

ppp multiling

no ppp multilink fragmentation

multilink-group 1

sh

exit

Description 1.544M 1 of 2

.....

Description 1.544M 2 of 2

.....

It would appear to me that there are 2 T1 lines combined by the router into 1 internet connection. Would you agree?

1. What would happen if I unplugged 1 of the 2? I would assume that I will loose the internet connection? If not, how could I tell if one of the lines is "out of order"? The T1 appears to be coming out of a phone jack right into the router. Isn't there usually a smartjack somewhere close by that you can check for errors?

jgreenwoodii
Level 1
Level 1

To answer the question it depends on the setup of your router's connection to the internet. The two T1's could be bundled together to provide you a 3Mbps Internet connection. Or they could be individual T1's to provide Internet redundancy in case one of your T1 goes down. There could be a # of reasons but ultimately he should consult with your Network Administrator/IT department. It could also be your Internet Service Provider's equipment as well so be careful.

HTH

Jonathan

Shelly

One thing that your boss should cosider in this is that if he does remove 1 of the T1s he will most likely cut in half his bandwidth to the outside world.

The cable connected to the Fe0/0 provides 100 Mbps (or perhaps 10 Mbps depending on what equipment it connects to) providing access to the inside network. The T1 provides 1.5 Mbps each. As the previous posts have pointed out we could tell more definitively if we saw the configuration of the router. But in eliminating a T1 your outside access probably goes from 3.0 to 1.5.

And the other aspect to consider is that the 2 T1s probably give some redundancy for connectivity to outside. If 1 T1 is eliminated you will introduce a significant single point of failure.

So I suggest that your boss consider carefully the implications before deciding to eliminate a T1.

HTH

Rick

HTH

Rick

Thank you.

Nothing drives me crazier then the standard "contact your administrator" answer. I am the LAN Administrator! The guy asking the question is the Manager of IS!!!!!

I know a bit about "routers" (having installed about 300 Linksys and Netgear) but I don't know anything about Cisco routers or how they interface with the T1. Generally, in a small network like ours this is handled by a consultant since it is setup once and generally needs little or no ongoing maintenance. The person who set this up is no longer available so I have been asked to "look into it".

Okay, but to be fair to Jonathan you did say you knew nothing about routers :-)

We really need to look at the config to even begin to help you. This router is under your companies control ?

If so, do you know how to log into a Cisco router ?

Jon

Not sure if my previous post made it but I apologize Shelly, I was just responding to the first 6 words in your original post:) Sounds like from previous post your in good hands, hope all works out for you.

R/

Jonathan

Apology accepted. Guess I should have been clearer. I know nothing about Cisco routers!

I located a printout of the configuration.

It is described as DS1 3Meg Managed ISP via multi-t1.

Without retyping the entire configuration, the things that stand out to me are as follows:

Interface Multilink1

description : MDG: 3M: S3/0/0/23:0 ....

no cdp enable

ppp multiling

no ppp multilink fragmentation

multilink-group 1

sh

exit

Description 1.544M 1 of 2

.....

Description 1.544M 2 of 2

.....

It would appear to me that there are 2 T1 lines combined by the router into 1 internet connection. Would you agree?

1. What would happen if I unplugged 1 of the 2? I would assume that I will loose the internet connection? If not, how could I tell if one of the lines is "out of order"? The T1 appears to be coming out of a phone jack right into the router. Isn't there usually a smartjack somewhere close by that you can check for errors?

Shelly

I am glad that you found a copy of the router configuration. It makes this discussion easier.

Yes that means that both of the T1s are logically combined to provide a single logical connection to the outside world.

If you unplugged 1 of the 2 T1s I would expect the logical interface to remain up and active (but operating at only 50% of normal capacity). Without the ability to access the router and monitor its components the main way to tell if one of the T1s has failed is to wait for the provider to call and inform you of the problem (and given the performance of many providers I would not want to depend on that)

Usually there is a smartjack. It may be close to where the T1 service enters the building and the circuit may have been "extended" from the smartjack to your router interface.

HTH

Rick

HTH

Rick

Thank you.

Now that being said, my boss is worried because he is under the impression that the T1 is very "big" and 2 of them combined surely would be more than 1 cat5 at 100mb can make available to the network via the switch! LOL! Am I missing something here? Isn't the T1 1.5m so 2x 1.5m = 3m? Isn't this 3m "slower" than the 100m port going out, therefore isn't there little likelihood of this one port to the network will ever cause a bottleneck?

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