David Bombal on Twitter: "Paul tries to configure a loopback interface on a Cisco router with a loopback address. The router, however, displays the following error. Why is this configuration invalid? #CCNA #
![IPSec VPN connection to Cisco ASA with loopback interfaces on internal GRE routers - Discussions - Sophos Firewall - Sophos Community IPSec VPN connection to Cisco ASA with loopback interfaces on internal GRE routers - Discussions - Sophos Firewall - Sophos Community](https://community.sophos.com/cfs-file/__key/communityserver-discussions-components-files/126/0535.Typical-regional-office-setup.png)
IPSec VPN connection to Cisco ASA with loopback interfaces on internal GRE routers - Discussions - Sophos Firewall - Sophos Community
![cisco - Whats's the function of a loopback interface in routing protocols? - Network Engineering Stack Exchange cisco - Whats's the function of a loopback interface in routing protocols? - Network Engineering Stack Exchange](https://i.stack.imgur.com/TLEFV.png)
cisco - Whats's the function of a loopback interface in routing protocols? - Network Engineering Stack Exchange
![Fred de Jonge | Cisco Router - Site to site configuration on a router with 2 BGP interfaces and 1 Loopback interface with External IP. Fred de Jonge | Cisco Router - Site to site configuration on a router with 2 BGP interfaces and 1 Loopback interface with External IP.](https://freddejonge.nl/wp-content/uploads/2012/05/image1.png)