If you experience this issue, a router reload will resolve this problem. The very first interface to be activated is the loopback interface: ifconfig lo 127.0.0.1. Basically this warning is letting you know that once you remove a logical or sub-interface using the no interface command there is the potential for some of the previous configuration to return when re-creating the same interface. ISP routers usually have multiple external paths. This has been an issue with Cisco IOS for years and it has yet to be fixed. Telnet to router using loopback address, not interface address. Once youвЂ™ve removed the interface youвЂ™ll notice a warning that not all config may have been removed and may reappear after reactivating the logical-interface/sub-interface. %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback1, changed state to down %LINK-5-CHANGED: Interface Loopback1, changed state to administratively down % Not all config may be removed and may reappear after reactivating the logical-interface/sub-interfaces Router(config-if)# no interface loopback 1 Objective 2 request that we remove the Loopback 1 interface, you can remove loopback interfaces by negating the interface command using the no interface loopback # command as shown below As per the objective youвЂ™re required to configure the IP address 10.233.21.251/24 on this interface as shown below %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback1, changed state to upДЄfter the interface is created youвЂ™ll notice the interface changes to state up instantly. Configuration shown below Д®nter configuration commands, one per line. All other tradenames are the property of their respective owners.To create a loopback interface you need to navigate to global configuration mode and execute the command interface loopback # The interface is created automagically. WatchGuard and the WatchGuard logo are registered trademarks or trademarks of WatchGuard Technologies in the United States and/or other countries. The loopback interface IPВ address also enables load balancing when multiple paths are available. The loopback IP address and the attached subnets remain in the routing table even if one of the Firebox interfaces goes down. Because the loopback interface IP address does not depend on the link status of any interface, it is always up unless the attached router goes down. The loopback interface guarantees the Firebox can be contacted when there are multiple paths to the dynamic routing peer. In the dynamic routing configuration, use the loopback interface IPВ address, not the interface name. In the dynamic routing configuration, use the loopback interface IP address instead of a physical interface IPВ address. The IPВ address is added to the Secondary Networks list.ДЄfter you configure the loopback interface, you can use it for dynamic routing. In the IPВ Address text box, type the IPv4 network IPВ address to add.The Add a secondary network dialog box appears. To add a secondary IPВ address to the loopback interface:.The loopback address is the reserved network interface that is used by the local machine. In the IPВ Address text box, type the IPv4 address and subnet mask. In Example 51, the IPv4 address 127.0.0.1 is the loopback address.(Optional) In the Interface Description text box type a description for this interface.This can be useful for testing purposes or as a. To configure the primary loopback interface IPВ address: You can define a virtual loopback interface by assigning an IPv4 or IPv6 address to the lo (local) interface.You must configure the loopback interface in the network settings before you can use it in the dynamic routing configuration. You cannot use the loopback interface in policies as the local gateway IPВ address of a BOVPN or BOVPN virtual interface, or as the destination in a static network route. The loopback interface is supported in routed mode only. In the loopback interface configuration, you can specify a primary IPv4 address, and you can add secondary networks. A loopback interface can increase the stability of dynamic routing through a multi-WAN connection because it ensures the consistency of the next hop and avoids the potential for BGPВ routing oscillation. You can use the loopback interface for dynamic routing to multiple ISPs when your Firebox is configured with multi-WAN. If your Firebox runs Fireware OS v11.11 or higher, you can enable a loopback interface on your Firebox, which is a virtual interface assigned to the Firebox that is not associated with a specific physical interface.

Loopback interface