IP address unnumbered
When an interface will only use an IP address for a short period, it can borrow an IP address from another interface to save IP address resources. Usually, the interface is configured to borrow a loopback interface address to remain stable.
Router ID
Some dynamic routing protocols require that routers have IDs. A router ID uniquely identifies a router in an autonomous system (AS).
If OSPF and BGP are configured with router IDs, the system needs to select the maximum IP address as the router ID from the local interface IP addresses. If the IP address of a physical interface is selected, when the physical interface goes Down, the system does not reselect a router ID until the selected IP address is deleted.
Because the loopback interface is stable and usually Up, it is recommended as the router ID of a router.
BGP
To prevent BGP sessions from being affected by physical interface faults, you can configure a loopback interface as the source interface that sends BGP packets.
When a loopback interface is used as the source interface of BGP packets, note the following:
The loopback interface address of the BGP peer must be reachable.
In the case of an EBGP connection, EBGP is allowed to establish neighbor relationships through indirectly connected interfaces.
MPLS LDP
In MPLS LDP, a loopback interface address is often used as the transmission address to ensure network stability. This IP address could be a public network address.
SNMP
To ensure the security of servers, a loopback interface address is used as the source IP address rather than the outbound interface address of SNMP trap messages. In this manner, packets are filtered to protect the SNMP management system. The system allows only the packets from the loopback interface address to access the SNMP port. This facilitates reading and writing trap messages.
NTP
The Network Time Protocol (NTP) synchronizes the time of all devices. NTP specifies a loopback interface address as the source address of the NTP packets sent from the local router.
To ensure the security of NTP, NTP specifies a loopback interface address rather than the outbound interface address as the source address. In this situation, the system allows only the packets from the loopback interface address to access the NTP port. In this manner, packets are filtered to protect the NTP system.
Information recording
During the display of network traffic records, a loopback interface address can be specified as the source IP address of the network traffic to be output.
In this manner, packets are filtered to facilitate network traffic collection. This is because only the packets from the loopback interface address can access the specified port.
Security
Identifying the source IP address of logs on the user log server helps to locate the source of the logs rapidly. It is recommended that you configure a loopback address as the source IP address of log messages.
HWTACACS
After Huawei Terminal Access Controller Access Control System (HWTACACS) is configured, the packets sent from the local router use the loopback address as the source address. In this manner, packets are filtered to protect the HWTACACS server.
This is because only the packets sent from the loopback interface address can access the HWTACACS server. This facilitates reading and writing logs. There are only loopback interface addresses rather than outbound interface addresses in HWTACACS logs.
RADIUS authentication
During the configuration of a RADIUS server, a loopback interface address is specified as the source IP address of the packets sent from the router.
This ensures the security of the server. In this situation, packets are filtered to protect the RADIUS server and RADIUS agent. This is because only the packets from a loopback interface address can access the port of the RADIUS server. This facilitates reading and writing logs. There are only loopback interface addresses rather than outbound interface addresses in RADIUS logs.