Loopback address (lookback)

Loopback address (lookback)

 

 Lookback is the loopback address on the router. It is a virtual interface.Ensure that the routeId. This interface does not have link failure.

Generally, lookback is configured during testing. This interface is the loop interface on the vro, which has the effect of matching the clock frequency. Unlike the protocol on both sides of the physical interface, it can only match the clock frequency,

During the experiment, we usually configure lookback on the router to reduce the number of physical interfaces that need to be configured. in use, it is generally used to expand the ping command, you can enter the source IP address as the lookback address and the destination IP address as the destination CIDR block to test the connectivity of the link.

 

 

 

 

 

What is the specific use of the return port of a Cisco router?

 

 

    The loopback port is stable and has no possibility of failure. For example, if your vro has multiple interfaces connected to the network, you can telnet only the IP address of one interface for security reasons, however, when this interface fails, you cannot log on to the vrotelnet. If you use the loopback port as the Telnet management address, as long as you have a physical interface to connect to the network, then you can log on to the vro. Of course, the premise is that you have advertised the route of the loopback port to the network. For example, if your BGP session uses a physical interface for connection, once the physical interface is down, the BGP neighbor will be down. When the physical interface is up, you need to re-Initialize BGP and perform route convergence, this is quite performance-consuming and time-consuming. If you use the loopback interface as the interface for BGP session, even if the current link is interrupted, however, as long as there are other links in the network that can reach the other end, the BGP session will not be reset, ensuring the network stability. Of course, loop loose can be used in many ways, but its features are mainly reflected in stability.

    The loopback port is a virtual port and is always in the up status. Through it, the as connected by BGP can always be connected without changing the status of the border router port.

 

 

 

 

 

 

 

What is lookback on a vro?

    For example, what is the relationship between my route loopback configuration and the gateway? If a static route does not need to be configured on the route, can I go back to this kind of route?

 

Lookback is a logical port completely specified by the Software. Its biggest feature is that it supports all platforms and its status is always up. According to this feature, we apply it in many places. For example:

1. As the ID of the router device, in OSPF and other protocols, the Protocol specifies that the router is assigned according to the routerid, because the loopback port is always valid, therefore, we usually create a loopback port and encapsulate the IP address as the router ID. The Protocol first compares the IP address size of the loopback port to select the router for routing.

2. As a non-direct connection CIDR Block of the routing device, the loopback port is configured with a CIDR block other than the direct connection CIDR Block of the router and other devices. You can test the routing between devices, this is also a very effective and convenient way to check device connectivity.

3. As the terminal access address, because the loopback port will never go down, it is a common method to use its port address as the address for Telnet access from other terminals and devices, det implementation.

4. As a "black hole" processing, because the packet routed to loopback will be re-routed back to the loopback port of the router and will not be actually forwarded, therefore, it can also be used as a "black hole" of a route. Now it is also implemented using a NULL Port, which can be considered as a recycle bin.

     We recommend that you systematically learn the routing work manual.

 

 

 

  The role of the loopback interface:

  Local loopback interface (or address), also known as loopback addressAddress).

  This type of interface is the most widely used virtual interface, which is used on almost every vro. It is commonly used for the following purposes:

  1As the management address of a vro

  After the system administrator completes the network planning, a loopback is created for each vro for convenient management.And specify an IP addressThe Administrator uses this address to remotely log on to the vrotelnet (Telnet.

  But there are usually many interfaces and addresses on each vro. Why don't you choose one of them?

  The reason is as follows: Due to telnetCommand to use TCPA router interface is down due to a fault.But other interfaces can still be used for telnet.That is, the TCPThe connection still exists. Therefore, select TelnetThe address must be never downAnd the Virtual Interface meets this requirement. Because this type of interface does not require interconnection with the peer end, to save Address Resources, loopbackThe interface address is usually set to 32Bit mask.

  2Use this interface address as the dynamic routing protocol OSPF, BGPRouterIDDynamic Routing Protocol (OSPF), BGPYou must specify a router for the Protocol during running.IDAs the unique identifier of the vro and must be unique within the autonomous system. Because RouterIDIs a 32The unsigned integer, which corresponds to the IP address.The address is very similar. And IPThe IP address is not duplicated.IDIt is specified to be the same as the address of an interface on the device. Because loopbackInterface IP AddressThe IP address is generally regarded as the router identifier, so it becomes a router.ID.

  3. Use this interface address as the BGPEstablish TCPSource Address of the Connection

  In the BGPProtocol, two running BGPTo establish a neighbor relationship between vrouters through TCPThe connection is established.

  Loopback is usually specified When configuring neighbors.The interface is used to establish TCPThe source address of the connection (usually used only for ibgp, The reason is the same as 2.1To enhance TCPConnection robustness)