Pinging a router on a closed circuit

[pietb]

Hi,

Let me start by saying that I am not a network administrator but currently we are one network administrator short here at our company. A co-worker of mine began this task but we are running into dead ends.

Our last question here at tek-tips asked if there were tools out there to monitor our closed circuit network (see

http://www.tek-tips.com/gviewthread.cfm/lev2/8/lev3/58/pid/557/qid/871598a).

Our problem was that we don't have the community string for our router, which these tools required. (Any advice?)

So, here comes my next question. We have two routers in a closed circuit. One is located here in our network which we can ping. The other is located on the other side of the country. Is there anyway we can ping the router that is on the other side of the country? At this point it appear we can't. Can anyone explain to us why?

Thanks for your help.

Piet


---------------------------
Pieter Bergmans

http://www.portal2hp.com

- "Come discuss your enterprise and business class HP equipment

 

[rburke]

Well it is fairly common practice to block the ICMP "ping" packets on inbound interfaces on routers. There are a range of reasons, but they all are security related.

As to being able to ping it, that would require getting the configurations from the router and then verifying that it was the configuration to block those ping packets and modify it if needed. Are the circuits passing data? If you just want to see if you can get a response from the router then you could always try to telnet into it and if it returns a username or password prompt then you know it is running.

But without configs it is impossible to give you all the reasons that you can't ping it.

Let me know if there is anything I can help you with.

Burke

 

[pietb]

rburke,

Thanks for the reply. I tried to telnet into the router and it gave me the following error:

-------------------
Could not open connection to the host, on port 23: connection failed
-------------------

Does this mean that the router is not working? And, yes, we pass data between the two routers just about every minute of the working day. Also, if I might add (in hopes that it may make our situation clearer), this is the setup as far as I know it: We have an SNA server here at our company which is attached to a Cisco Router which is connected to another Cisco Router on the other side of the country which is then connected to a MainFrame.

You mentioned something about the routers configuration. How can I obtain that? Is there software? Do I telnet into it? Lastly, in your opinion, what is the best way to monitor this connection for uptime/downtime? We had a company quote us a rather large figure to install a device at our company and then an additional monthly charge to monitor it. Does this make sense? We were hoping for a nice Open Source alternative but many of those seem to be based on Linux.

Thanks again.

Piet

---------------------------
Pieter Bergmans

http://www.portal2hp.com

- "Come discuss your enterprise and business class HP equipment

 

[lgarner]

Telnet may also be blocked. Who owns the remote router? Can you telnet to the local router? Getting the configuration is a matter of telnetting in and uploading it to a tftp server (or just looking at it).

Try ssh. If it's a fairly new router then it may support ssh access. Perhaps telnet is blocked and ssh is open.

If you can ping the serial interface of your local router, that's one way to detect a link up/down. It'll stop responding if the link is down.

I use open source tools for monitoring links, but there are inexpensive options also. WhatsUp Gold is good. I think that there are some that are also free for a small number of hosts- a product called "Servers Alive" or something like that comes to mind.

You could spend a lot of money monitoring this, but it's overkill for one link. On the other hand, one link probably isn't worthwhile for the monitoring company unless they charge a bit for it.

 

[pietb]

Thanks lgarner,

Yes, I can telnet into the local router. I tried to SSH to the remote router (which we own) using puTTy but no luck. Tell me something, am I at a total loss if I don't know the passwords to either of these routers? When you say "ping the serial i/f of our local router", do you mean ping the IP? Or do you actually ping the serial i/f? How would I do that? And, pinging the local interface would tell us if the local router was up but we still would know nothing on the remote side, right?

Any more thoughts would be great.

Thanks,

Piet

---------------------------
Pieter Bergmans

http://www.portal2hp.com

- "Come discuss your enterprise and business class HP equipment

 

[rburke]

Who is in charge of the routers? Whoever that is should have the passwords to both. If you can get the passwords then it would be possible to setup a SNMP community and/or allow pings from certain machines. Then it would be possible to use MRTG or other monitoring software to keep track of the connection.

Another option would be to use the Syslog messages and log them onto a Syslog server which you could then view. Then you could monitor when the connection goes down. But again, that would be something that you would have to get into the configuration of the router and know the telnet and enable passwords.

Burke

 

[lgarner]

If you don't know the passwords to a router, they can be reset by following the instructions at

http://www.cisco.com/en/US/products...ducts_password_recovery09186a0080094773.shtml

This involves rebooting the routers a couple of times, and requires physical access to it (via serial port). If these routers belong to you but no one knows the passwords, I'd strongly suggest following this procedure and documenting the passwords somewhere safe.

Normally (but not always) each interface in a router will have an IP address. If the interface is up, the IP address can be pinged. If not, due to a link or remote router failure, it won't reply. This assumes that the serial interface is logically connected directly to the other router: point-to-point, for example. If the link goes down, it's like cutting a cable. Each router immediately senses the loss of the link.

This won't work if there is an intermediate device. For example, if two routers are connected via a hub then this test won't work. The loss of one router won't trigger the interface status on the other.

This is one way to test a link, but it depends upon your knowing something of your router's configuration, which depends upon your knowing the passwords... you get the idea.