![]() Perhaps the original poster can clarify the reasons that they chose to implement loopback interfaces on layer 2 switches. I think that they would be as well off (and configuration would be more simple) to have remote management use the VLAN 1 interface address as a loopback address. But in this situation there is only a single layer 3 path and they are entirely dependent on the operation of the VLAN 1 interface. Loopback interfaces have a real advantage when there is more than 1 layer 3 path to the device. It just complicates things and I do not see any real advantage in it. My opinion is that if they want to operate the access switches as just layer 2 switches, that there is no real advantage in configuring loopback interfaces. But I think that you did well to demonstrate a way to get it to work. Whether it is fair in terms of the original question would depend on the full environment of the original question which we do not know. I would say that what you did is quite fair as a way to find what works. Based on the symptoms described I am guessing that they have not provided static routes in the core for the access switch loopbacks, which you did. Your localhost is used to refer to your computer from its 'internal' IP, not from any 'external' IPs of your computer. Then we would know better what they are trying to do. You are not pinging the same interface, without any physical interfaces you still have a 'local host'. This gives us the same experience that a normal user gets when connecting from their browser.As I said in my post: seeing configs would help. For example, we can test a web server running on our machine by connecting from a browser to the loopback IP address and the web server port. ![]() ![]() The loopback interface can also be used by services and applications to communicate with each other on the same machine. Here we verified that our network stack has no issues because we got a reply, and the traffic actually never left the machine. If there’s a reply, it means that the TCP/IP stack is working fine and able to process packets: $ ping localhost This can help in troubleshooting scenarios where we want to isolate and identify if a network issue is caused by an internal problem inside the machine network stack itself.įor example, we can try to ping the localhost and verify if there’s a reply or not. However, because the loopback interface is only an internal virtual interface with no physical hardware, the machine can use it anytime to communicate with itself. IPv4 assigned within the network (here 192.168.1.15) So, when you access/ping 192.168.1. There are basically 3 ways to access localhost 127.0.0.1. Here we can see a mapping between the localhost hostname and the loopback IP address 127.0.0.1. By pinging that address you are actually pinging the localhost or the same 'server' on which you are currently working on. If I remove all the crypto config, the tunnel comes up fine as just an GRE tunnel. We can verify this by checking the hosts file: $ cat /etc/hosts As soon as I change the tunnel source to use the loopback IP, change the crypto map ACL, and move the crypto map from the WAN interface to the loopback interface, the tunnel will not come up. There’s also a hostname localhost assigned to this IP address by default. We can see that the lo interface has an IP address of 127.0.0.1, with a netmask 255.0.0.0, which is equivalent to /8. The eth0 is a physical ethernet interface, and the lo is our loopback interface. TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 So let’s check the details of this interface using the ifconfig command: $ ifconfig
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