Cisco 1700 wont ping another Cisco 1700

[samdaman]

Im having problems connecting two Cisco 1721 Routers back to back via the FastEthernet ports on both routers, they are connected via a crossover cable. From my pc I can telnet into router A and ping the ethernet0 and fastethernet0 ports on Router A, but no ports on router B.

However the show ip route command clearly shows connectivity that each router detects the other.

I have subnetted the network 192.168.0.0/28
Router A
ethernet0 192.168.0.1
fastethernet0 192.168.0.17
Router B
ethernet0 192.168.0.33
fastethernet0 192.168.0.49

I have started the configuration from scratch, so 90% of the defaults are in place. I am new to this so it might seen like a stupid question. Also not sure if I need to specify encapsulation between ports, or enable some routing protocols like RIP, or OSPF.
Any help would be greatly appreciated

Thanks and kind regards

Sam

 

[macanudo]

how do you know each router sees each other?
from the config i can't see any routes out of router A.

router A has:
e0 192.168.0.0/28
f0 192.168.0.16/28

router B has:
e0 192.168.0.32/28
f0 192.168.0.48/28

inside route A you can ping both interfaces since one is connected to your computer and the other is crossovered with the other router (i mean both interfaces are up), but since router B has two different networks associated with it, unless running some igp to exchange information, both routing tables have to be built manually.

still there's a catchy issue: the 'crossovered' interfaces don't have a chance of exchanging information since they are each one in different networks. you could do this with serial links running ppp, but not with ethernet i'm afraid.

hope this may help.

cheers, gabriel.

 

[samdaman]

Thanks Gabriel for your reply

Now I look at the IP route for each of the interfaces, it only shows the ethernet ports of their own router. So if I was to change the Fast Ethernet port for router B, to be on the same network for Router A would this be ok?

also

Do you know if I can connect the two routers via the aux ports? and if so, do I still use a cross over cable?

Thanks for your help

Kind regards

Sam

 

[macanudo]

hi sam.

yes, if you use ip addresses from either networks 192.168.0.16/28 or 192.168.0.48/28 (the ones you assigned to fe ports, but could be anything) to both interfaces, it would work.

the thing here is that ethernet does not support point-to-point connections (though that's not entirely so, but let's stick to this rule for the time being...), you can assign different ip addresses to each end side of the link running ppp for instance.

basic ip talk involves both parties to be on the same logical network, that doesn't mean you can't run several different ip networks over the same shared media; you can, and as a result, devices on the same logical net can talk to each other, but not to other networks, unless a layer-3 device (a router), can do proper gatewaying between the nets.

not a problem connecting the routers via aux ports. you would have to configure the async interfaces on both routers, run ppp/slip with a crossover (they are both dte devices) and done.

hope this is not too long and helpful ;-)

cheers, gabriel.

 

[samdaman]

Dont worry, your text isnt as long as its taking me to do it on my own ;-) and is very helpful. In fact your first reply helped me with other problems, which I have now solved.

Basically, I have been given two routers and the course material (which I have laboriously covered) from the Interconecting Cisco Network Devices course by my boss to crash myself into becoming a Cisco administrator. Whilst the book was helpful, and not beyond me, it lacks the teacher to go with it.

So I reconfigured the IP address, and from Router A I am now able to ping the FastEthernet port on router B. Yahoo

However I was not able to ping the Etherenet port on router B. Then I enabled classless IP routing on both routers and presto, I was able to ping all ports on both routers. Thought I had cracked it finally, however....

I have a pc connected to a Hub that is connected to Ethernet0 on router A. I can ping Ethernet0, but not FastEthernet0 on Router A. I did the same for Router B and also recieved destination host unreachable.

I assumed that if the routers could see all interfaces, then when it recieved a request on the ethernet port, it should be able to find the correct interface, or at least pass it onto router B.

What am I doing wrong here?

(I promise that I wont write any more novels for you to digest)

 

[macanudo]

don't worry, you know what they say: no pain, no gain.

i assume you have your routing tables right, otherwise you couldn't have had ping working on router's B eth port.

now to the gory details.

if you and router A are connected to the same hub (sharing a common network number) it is obvious to ping it successfully.
why can't you get to fe on port A? two options: either you don't have a static route in your pc to router's A fe port (i mean the network that it's associated with it) via router A eth, or your default gateway is not router A. either way it makes sense.

if you put a route in your pc to reach the network both routers use to communicate (the fe ports), you are specifically going through a certain path. you can miss that.
if router A is the gateway, then destination networks (or hosts) which the pc is not aware of will be sent through it.
the response you get depends whether the routers actually are aware of each other's routes.
for instance in your current setup (i'll call A-e and A-f the interfaces on router A, and the same for router B) you can directly reach A-e. if there is a static route or router A is the gateway, then you have no problem reaching A-f.
B-f will work no matter what you choose (as long as you do some of the two options), since if there is a static route, both fe interfaces are ont he same network (no problem), and if router A is the gateway it know (router A) how to get to the other end.

but beware of B-e, because it is on another network, and then you either put a static route on your pc or if gatewaying through router A, a route towards that network (where B-e sits), has to be entered into the routing table.
the same goes to router B, you have to put a route to get back to the network where A-e and your pc are.

happy? ;-)

it's not that big deal actually.
the other thing that you can do is have router A as default router and configure rip on both boxes.

router-a(config)router rip
router-a(config-router) network 192.168.0.0/28
router-a(config-router) network 192.168.0.16/28
router-b(config)router rip
router-b(config-router) network 192.168.0.16/28
router-b(config-router) network 192.168.0.32/28

that's it. each router has complete awareness of the topology. if you go via A-e you can ping any of the interfaces and only be worried if the coffee is not warm enough.

=)

gabriel.

 

[samdaman]

Hi Gabriel

Thanks for the solution. Funily enough I did some of what you suggested.

I made ae (ur short port versions)the default gateway on router a, and ae on router b the default gateway, and bingo i could ping from one pc to the other and vice versa. I suppose that because I made the ip classless route between both routers that they passed requests on to each other.

thanks for the help.

Sam