Another Ping Question

LearnAsIGo

What follows is probably laughable to most everyone here. No worries though, it's happened before.

I don't know how to learn ip addresses of specific interfaces on another router.

show route - nothing shows up

show ip route - subnets show up

debug all - stuff about "R2" but still no ip addresses.

Version 12.1 - yes, I understand this is old.

R1#sh ip route

<clipped to keep it short>

C 192.1.1.0/24 is directly connected, Ethernet0
C 192.2.1.0/24 is directly connected, Serial0
C 192.3.1.0/24 is directly connected, Serial1

R1#ping 0.0.0.0

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 0.0.0.0, timeout is 2 seconds:
.
Reply to request 1 from 192.1.1.2, 4 ms
Reply to request 2 from 192.1.1.2, 4 ms
Reply to request 3 from 192.1.1.2, 4 ms
Reply to request 4 from 192.1.1.2, 4 ms

R1#

The wild idea of "ping 0.0.0.0" popped into my head. So why not?

So one ip address learned, two more to go.

Bottom line ===> How do I learn ip addresses of interfaces? Other commands? Other debugs?

rakem

are you familiar with CDP (Cisco Discovery Protocol)

do some show cdp commands and see what you get

show cdp neighbour detail will give you IP addresses of directly connected cisco devices.

LearnAsIGo

Hi Rakem,

That was what I originally did - the EASIEST WAY , but I read somewhere about security best practices and they say to disable cdp.

So I disabled cdp on R2 and wouldn't allow myself to plug into the console port of R2.

I was just wanting to know is it still possible to learn interface addresses if you're stuck without any documentation to refer to, and cdp is disabled, and you don't have any network enumeration software.

Reason I'm asking is, a few days ago, I was asked to help someone who had telnetted into his home router and couldn't get into the other router because he didn't know the ip addresses. Needless to say, I was a bit embarrassed because I couldn't do it either.

rakem

i don't know of any other way to get an ip address.... maybe someone else knows?

LearnAsIGo

No worries, there.

Maybe I'm just making mountains out of molehills, or maybe I'm wandering into Rube Goldberg-ish type performance. I don't know.

It's just one of those things that stays in the back of my mind. I tend to be tenacious with a topic I'm interested in and would like to know what "angles" are there to this.

I have a feeling maybe the answer I'm looking for is in the unix/linux realm?

Guess I'll just have to find out as I gain experience/knowledge.

outstream

show cdp neighbors detail gives the configuration details about layer2 connectivity. if you have disabled it and u still want to learn ip addresses of the devices with whom your router can talk, then the command is show ip route to get layer 3 connectivity details.
since you have mentioned this command already, and nothing is learned about other devices, then i presume no routing protocols are activated on ur router and hence its not communicating with any other router. in a scenario like this, i guess the only possible command is show cdp neighbors detail. enable it, learn the addresses and disable it back again.:D

Cucumber

Assuming CDP is not available.

Have you tried the extended ping?

#ping
...
Target IP address: 0.0.0.0
...
Extended commands [n]: y
Source address or interface: serial 0
...

It would be interesting to see what this does.

BTW, for ethernet interfaces
show ip arp
may help to know what other interfaces are connected to the LAN.

malcybood

you can also get it via pinging a DNS name if you have setup dns. An easy way for you to do this for now until you are more familiar with the IOS is to add the ip host command in for example:

you have
lab_a - 3 interfaces
s0/0 - 223.8.151.1
S0/1 - 192.5.5.1
FA0 - 201.100.11.1

To add these DNS entries int lab_b to enable hostname resolution you would do the following:

lab_b(config)#ip host lab_a 223.8.151.1 192.5.5.1 201.100.11.1

Now when you are logged into lab_b you can do the following which will resolve the ip address:

lab_b#ping lab_a

Play about with it and familiarise yourself with this as there may be some questions in the test about the ip host command. There are more advanced ways of putting DNS into a router like ip domain-lookup but I'd say learn the basics first.

(because this is a manual process to ping lab_b from lab_a you would need to add the dns entries into lab_a router as above but for the correct router ip addresses. Can get messy if you've got more than 3 or 4 routers but it is okay for getting the idea)

The only other way I know is the sh cdp neighbors detail command