Loopback Interface with public IP

[Raja Ali]

Hi All,

Requesting your kind help on the below scenario testing

We have configured Public IP in one of the WAN interface 

2.2.2.8 255.255.255.224

Have configured loopback with below public IP

2.2.2.100 255.255.255.255

When i tried to ping some destination  with source as WAN interface IP i am able to ping  and with source as loopback IP i couldn't

However from the destination end i am able to ping both the WAN interface and loopback IP

Please help me to understand what i am missing 

[MHM Cisco World]

when you add ip to loopback do you get log message that this ip conflict ?
I think since the IP is in same subnet you will face reachablility issue.

[Raja Ali]

.Even though it falls on same master subner 2.2.2..0/24

At WAN Interface i had configured as 2.2.2.8/27 and had used 2.2.2.100/32 at the loopback interface end.

As i mentioned from outside i am able to ping both the IP. From inside with source as WAN IP (2.2.2.8) i can ping the destination with the source as loopback ip (2.2.2.100) I couldn't ping the destination

Is this possible ? am i missing anything interms of routing

Note : I didn't get any error log while configuring the IP's

[David Ruess]

Hello,

They are not in the same subnet so that shouldn't be an issue. 

Check your routing. If you can ping from the destination to the WAN interface and loopback with the 2.2.2.0 addresses then most likely on your WAN (local) device you have a default route, so even if you dont have a specific route out it knows to send it out the WAN interface and reach the remote site. The remote site however may not have the reachability back. Routing is bidirectional. It has to know how to "answer back". So that being said the remote side probably has a route to the WAN interface of 2.2.2.8, but since the 2.2.2.100 address is in a different subnet from the WAN interface it doesnt know where its at. 

Check your routing table on the mote side to see if it has an entry for the 2.2.2.100 address. If not you may need to add it to your routing protocol or put in a static route to point it towards the WAN (local) device.

Hope that helps

-David

[Raja Ali]

At the remote side have configured route for both the IP's

[MHM Cisco World]

instead of ping use traceroute, 
if traceroute stop in your router then this issue in your RIB and config 
if traceroute stop in SP router that you must talk with them

[Raja Ali]

When i do the traceroute with the loopback (2.2.2.100) as source it stops at the first hop at the router itself

However the with the WAN interface IP (2.2.2.8) works

Do i need to configure any specific route for the loopback IP am i missing anything here. 

Looks like this has never worked earlier, and i had recently took over this issue. Any suggestion would be highly appreciable

[David Ruess]

Have you configured the loopback to be advertised like your other routes into the network?

Can you provide a show ip route from the WAN router and from the remote router?

[MHM Cisco World]

can I see show ip route ?
ONE important point, 
do you config ACL OUT/IN  WAN interface?
do you config NAT in WAN interface ?

[paul driver]

Hello
Disable proxy-arp  on the Wan interface if enabled and make sure you are advertising the loopback address

[Raja Ali]

Thank you all for your help and support, able to figure out the issue and it is resolved now. 

The IP was also used by some other services, which was the cause

[MHM Cisco World]

I mention this in first comment but, anyway,

Good job friend.