![]() 1 is the factory default setting, and thus, becomes the IP address. In computer networking, a single Layer 2 network may be partitioned to create multiple distinct broadcast domains, which are mutually isolated so that packets can only pass between them through one or more routers such a domain is referred to as a Virtual Local Area Network, Virtual LAN, or VLAN. Generally, VLAN Virtual Local Area Network. If you do not configure the loopback interface address, then the first configured VLAN Virtual Local Area Network. You must configure a loopback address if you are not using VLAN1 to connect the Mobility Master or managed device to the network. It will be routable from all external networks. ![]() To use this interface, ensure that the IP address is reachable through one of the VLAN Virtual Local Area Network. The loopback address is not bound to any specific interface and is operational at all times. Netmask defines the class and range of IP addresses. You configure the loopback address as a host address with a 32-bit netmask Netmask is a 32-bit mask used for segregating IP address into subnets. servers, and accepting administrative communications. It allows authentication, authorization, and accounting of remote users who want to access network resources. An Industry-standard network access protocol for remote authentication. tunnels, originating requests to RADIUS Remote Authentication Dial-In User Service. GRE is an IP encapsulation protocol that is used to transport packets over a network. This is done by establishing a virtual point-to-point connection through the use of dedicated connections, encryption, or a combination of the two. It enables a computer to send and receive data across shared or public networks as if it were directly connected to the private network, while benefiting from the functionality, security, and management policies of the private network. ![]() VPN enables secure access to a corporate network when located remotely. The loopback address is used as the Mobility Master or managed device’s IP address for terminating VPN Virtual Private Network. And this is the case where loopback address for router ID in OSPF is beneficial.The loopback IP address is a logical IP interface that is used to communicate with APs. But (!!) if any other router ( A, B, C or D) will have one (or more) of its interface(s) down, then if the router ID was not "set deterministically" - new advertisement will have to be sent onto the network, which will affected the overall bandwidth of it. On the other hand, if the router ID was set "deterministically" by configuring it to be the loopback address (or if there is any loopback address in the OSPF process), that will never go down (unless of course, the entire router/OSPF process will go down), then if any one of the interfaces of the router goes down, the router ID won't be affected, therfor no multicast OSPF "new router ID" messages will be sent onto the network.Ĭonsidering the above topology, in case router E (or more precisely its only interface) goes down, then anyway, when it will go up again it will still advertise its router ID "all over again". So, on any link failure for a specific router - if the logic of the router ID selection is still set on the "highest IP address" and there is no loopback address configured as well in the OSPF process (or there is no loopback address in the router at all) - then this link failure will trigger a new router ID selection procedure "within" the router and, perhaps more importantly, will obligate this router to advertise its "newly elected" router ID, meaning send OSPF messages again onto the network. This ID is chosen among ALL available interfaces on a given router UNLESS explicitly configured otherwise. As others mentioned, every OSPF router chooses a router ID. Adding to Maupin great answer I would further say that the (wise) choice of the router ID to be the loop back interface will be more "powerful" upon link failure scenarios.
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