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I'm trying to configure the phone configuration on my business' Cisco 2811 router. Without buying a bunch of dongles and connecting through the console port of the router, I'd like to try to SSH or Telnet into the router. My problem is that I don't know the IP of the Cisco 2811 router. The topology goes something like this.

DSL -> DSL Motorola Modem -> Cisco 2950 Switch -> Cisco 2811 Router -> Phones                                           
                                               -> Workstations

I'm pretty sure that the modem is acting as a DHCP server and being a pretty dumb modem it doesn't offer a DHCP table to show which devices are getting which IP's.

What I basically need to do is backtrack through a workstation, to the switch, to somehow get the IP of the switch and SSH/Telnet into the switch to find out which IP the router is getting. Once I have the IP of the router I can try SSH/Telnetting into the router and be able to configure it that way.

Someone please correct me if I'm wrong but would this be a way to go about this?

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  • Are the phones using the 2811 as their entire phone system (CUCME), or do they talk back to a centralized CUCM at another site?
    – Brett Lykins
    Nov 14, 2013 at 21:53
  • I'm about 90% sure that they use the 2811 as their phone system.
    – gh0st
    Nov 14, 2013 at 22:06
  • Thanks for the response, second question: If you do get the IP address of the 2811, do you know the login credentials?
    – Brett Lykins
    Nov 15, 2013 at 0:18
  • I'm pretty sure I can get them from the individual who set it up. If I can't, I thought there was a way to recover it without wiping the whole router config, correct?
    – gh0st
    Nov 15, 2013 at 1:33
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    Yes, you can recover the system, but that requires the "bunch of dongles" you don't want to buy for console access. (it's a standard RS-232 serial port. it comes from cisco with the necessary cable; or get one for $5 on eBay)
    – Ricky
    Nov 15, 2013 at 2:49

3 Answers 3

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If your 2811 is providing the phone services for your Cisco IP Phones at this site, finding the IP Address of the 2811 is relatively easy:

  1. Press the "settings" button on one of the phones
  2. Choose "Device Configuration"
  3. Choose "Unifed CM Configuration"
  4. Choose "Unified CM 1" or whichever says "Active"
  5. The listed IP address is the IP address of whatever device is controlling the phones (either the 2811 on site, or a CUCM at another facility)

The specific steps may vary depending on your phone models and firmware versions, but this should guide you in the right direction.

With all of that said, it really sounds like (based on your previous question and this one) that you're taking some stabs in the dark. I HIGHLY recommend checking out Jeremy Ciora's book from Cisco Press: "CCNA Voice 640-461 Official Cert Guide". It will help guide you through many of the questions you might have about Cisco IP telephony, and IP telephony in general. I've given it to several folks over the years, and it has helped them greatly.

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  • You seem to be well on your way to earning the nickname Mr VoIP :)
    – Mike Pennington
    Nov 15, 2013 at 13:44
  • @MikePennington This VoIP stuff is like a plague; now that I've touched it at work, I can't get rid of it. And no one will let me touch anything else. I miss routing and switching! :)
    – Brett Lykins
    Nov 15, 2013 at 13:46
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    Seriously I meant that in the best possible way, but I understand... I have the same problem with wifi at work
    – Mike Pennington
    Nov 15, 2013 at 14:01
  • I got the IP of the default gateway off of the IP phones of 10.10.10.1. The network of the ip phones and the network of the workstations must be on different vlans configured on the switch. I can't ping the 10.10.10.1 router from any of the workstations. I purchased, on ebay, a cisco console rollover cable which I also will need to buy the dongle for.
    – gh0st
    Nov 16, 2013 at 10:22
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Traceroute seems like your easiest option. Point it to something outside of your network (like google). Using that will resolve any device along the path.

root@xxx:~# traceroute -n google.com
traceroute to google.com (173.194.37.100), 8 hops max, 60 byte packets
1 x.x.228.1 0.429 ms 0.495 ms 0.615 ms
2 x.x.214.57 1.392 ms 1.997 ms 2.717 ms
3 x.x.6.53 15.051 ms 15.432 ms 16.069 ms
4 x.x.77.253 19.433 ms 20.015 ms 20.553 ms
5 109.159.254.132 17.706 ms 18.263 ms 18.615 ms
6 195.99.126.109 20.793 ms 21.157 ms 21.433 ms
7 209.85.252.186 20.599 ms * 20.774 ms
8 209.85.253.94 21.257 ms 16.791 ms 209.85.244.240 17.158 ms

root@xxx:~#

In the instance above, the router would likely be x.x.214.57.

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  • I thought of this but the only devices connected to the 2811 router are the phones. There are no available ethernet jacks/cards on the router for plugging in a laptop or PC.
    – gh0st
    Nov 14, 2013 at 21:30
  • @gh0st I think I misunderstood your setup. Just traceroute to one of the phones. You can get one of their IPs, right?
    – Ryan Foley
    Nov 14, 2013 at 22:17
  • I'm not sure. I'll give this a try tomorrow morning.
    – gh0st
    Nov 15, 2013 at 0:01
  • Or go to one of the phones and see what it's gateway is???
    – Ricky
    Nov 15, 2013 at 2:50
  • That would work too I just didn't think the phones had this kind of capability. Haven't worked in the realm of voip before. :/
    – gh0st
    Nov 15, 2013 at 7:03
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We can also use CDP to get IP address of directly connected device, for e.q from 2950 switch or workstation by sniffer. Sw2950> sh cdp nei * detail.

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