loop back question

[reddevilggg]

I've created 7 subnets with 3 routers using the Packet Tracer software from Cisco. All of it is configured and working fine. The problem is, there is another router which has an IP address for a ISP, so that my network can connect to this and i can configure it for internet access. I've been told that i can connect one of my routers to the 'internet' router using a loop back address, yet i cant seem to get this to work OR find much information about it.

Any help ?

[Rob Pomeroy]

Can you post a network diagram?

[Transfusion]

Okay I just downloaded Packet Tracer v5.3.2.0027, playing with it
Really is an interesting tool:

How did you set up the network?

[reddevilggg]

 Here is a copy of my network



Uploaded with ImageShack.us

The Warmingham router, in the centre, is connected to the Internet, the router on the right (router 0). The internet isp address 145.45.5.100. The warmingham router is connected to Subnet E, to the north, with a network address of 172.56.2.0/27 and 2 WANs.
WAN A, 172.56.2.32/30 on the left and WAN B 172.56.2.36/30 on the right

[Rob Pomeroy]

And which networks need to be able to route out to the internet?

[reddevilggg]

And which networks need to be able to route out to the internet?

All of it, through the Warmingham router, which is connected to the isp internet router (router 0)

[Transfusion]

I just connected Router0 and Warmingham with a Serial connection, manually set 145.45.5.100 as the IP address on Serial 2 on Router0, and Warmingham Serial 2 has an IP address of 145.45.5.101/16... but I haven't figured out how to get Static and RIP routing to work yet.

[reddevilggg]

There supposed to be some way to use a loop back address, apparently. I don't know though.

[Transfusion]

I figured I had to go Google after I realized my lack of knowledge about Router IOS commands and routing were severely limiting my progress

A loopback on a router has to be configured as a virtual interface. These have a *lot* of different uses, but to give just one example it can be used as a Router ID in an OSPF process if you don't want OSPF to pick the highest IP address of any physical interface on the router. In general, the loopback address is also the best one to ping to see if the router is up, since otherwise you'd be pinging the IP of a physical interface, and the router might be online via another interface if the one you're polling goes down.


Here's how you configure a loopback interface in Packet Tracer (or on a real router for that matter). In this example I just picked an IP address out of the sky (do NOT pick anything in the 127.x.x.x range since it is reserved for host loopbacks, and the router won't even let you do it):


enable
conf t
interface loopback 0
ip address 10.1.1.1 255.255.255.255
no shutdown
exit
exit
wr


You don't have to, but here I picked a subnet mask of 255.255.255.255, or a "host mask" since the loopback can be thought of as its own single-host network. Also you can make more than one loopback interface if you want.
Source(s):
CCNA, 1/2 CCNP

http://answers.yahoo.com/question/index?qid=20091110062813AAsrKeA
I hope this helps.