NOOB LOOPBACK Question

[WIZARD1325]

In the book it tells me that a loopback is a virtual interface card basically. So when I enable it "ip address and no shut"

why is it I cant telnet to it? 

nor can i ping it from the other router connect with a patch on same port 0/0 on each

[Georg Pauwen]

Hello,

the loopback interface indeed is a virtual interface that is not tied to any physical interface. It still is a layer 3 interface that needs to have the appropriate routing in place in order to be reachable. From which IP address are you trying to reach the loopback, and where is the default gateway for your IP address configured ?

[WIZARD1325]

Router 1:  192.168.1.1 255.255.255.0    .... f0/0

Router 2:   loopback5  50.50.50.5 255.255.255.0
Pinging from Router 1 to loop back 5. No bueno.
Pinging router 1 to router 2. 198.168.1.2  muy bueno

[Georg Pauwen]

Hello,

post the configs of both routers. What kind of routing do you have in place ? You need at least a default route on both routers:

ip route 0.0.0.0 0.0.0.0 x.x.x.x

where x.x.x.x is the next hop of the outgoing/connecting interface...

[WIZARD1325]

ahh yes the book was telling me to put a ip route of 0.0.0.0.0.0.0

but for some reason my router wasnt taking that command

i have a 2811

ill post what i have

[Deepak Kumar]

Hi, 

A look-back interface is a logical L3 interface but you can't make it physical or can't add with physical as like SVI. It is participating in routing as well as SVI and Physical interfaces. When we are designing the logical diagram for a client then as per client network, I also advise to the client for making a loopback interface as management interface and assign a management IP but you also keep in mind the routing configuration about lookback interface subnet also be done. A good thing about lookback interface is It will not goes down until administrator will not make it shutdown with a command or router/switch will not go down. 

If you configured correct routing then If any of one physical interface is up then you can access your device. But it depends on your routing configuration. Basically, I prefer to make it as management interface if special management physical interface is not available on the device or not possible to extend the special management network and dynamic routing as RIP/OSPF/BGP/ISIS etc is enabled on your network.

Regards,

Deepak Kumar