Router backup configuration (1)

Network Transmission of some key business data of some enterprises or organizations requires high reliability of network equipment and convenient maintenance. There are multiple backup technologies for Cisco routers. Here we will introduce the router's own backup technology and line backup technology. Generally, a router is a bridge between a LAN and a wan.
The so-called router's own backup technology is designed to solve some fault or local port fault of the router due to its hardware such as memory, CPU) or software IOS, network breakdown caused by the failure of the port or line of the connected local area device.
The router backup requires at least one router with the same functions as the active primary router. When the active router is paralyzed, it replaces the primary router in some way to provide routing services for LAN users. For LAN computers, how to find a backup router when the master router is paralyzed is as follows: proxy ARP, IRDP, dynamic routing, HSRP
1. Proxy ARP
Computers that support Proxy ARP send ARP broadcasts to find the MAC address corresponding to the destination address, whether they communicate with computers in different network segments or in this network segment, the router that knows the destination address will respond to the ARP request and broadcast its MAC address to the source computer. Then, the source computer will send the IP packet to the router, the router finally sends the data packet to the destination.
When the master router crashes and the computer communicates again, it will continue to send the Proxy ARP broadcast, back up the router to respond to the request and transmit data.
Disadvantage: if the main router is paralyzed when data is being transmitted, the computer that is communicating before another Proxy ARP request is sent. it is impossible to know that the master router is paralyzed and will continue to send packets to the router, resulting in transmission interruption, the computer that is in communication can find the backup router for transmission only after another Proxy ARP request is sent or restarted.
Cisco router support Proxy ARP
2. IRDP
Computers that support IRDP in the LAN will listen to the "Hello" multicast packet sent by the primary router. If the computer no longer receives the "Hello" message, it uses the backup router for data transmission.
3. Dynamic Routing
Some computers support dynamic RIP routing to find routers. The disadvantage of this method is that the conversion between the primary router and the backup router is slow.
The above three methods are mainly used on the computer side. The Cisco router provides the HSRP technology, which does not require any computer settings, the switching between the primary router and the backup router is transparent, and the switching speed between them is fast.
A group of routers that use HSRP for backup share a virtual MAC address and virtual IP address. Each local port that participates in HSRP has a local IP address and MAC address, each vro has a weight value, and the highest weight is used as the master router. Others do not work. When the master router is paralyzed, The vro with the highest weight will act as the master router, and so on. Vrouters regularly exchange weights to determine the working status of the vro. If the primary Router does not send this information packet for a period of time, other backup routers will think that the router is broken, and the backup router with a high weight will take over the virtual MAC address and IP address, responsible for data transmission. Once the primary router returns to normal, it will automatically switch back and take over data transmission again. Then, the backup router stops transmission and is in the backup state. In addition, HSRP allows the router to monitor the working status of some ports. Once the port fails, it also performs automatic failover.
　
In short, for LAN computers, there is only one gateway, that is, a virtual IP address. All the backup work is automatically completed by the router.
　
HSRP is applicable to the situations where the routes of the primary router and the backup router are exactly the same. Using the HSRP function, we recommend that you use dynamic routing protocols with fast convergence speed, such as OSPF and VPN.
Basic HSRP configuration steps:
Under port configuration, set the port IP address,
Ip address port IP address Subnet Mask
Enable the HSRP function under port configuration and set the virtual IP Address
Standby group number IP virtual IP Address
Only routers with the same group number belong to the same hsrp group, and the virtual addresses of all routers belonging to the same hsrp group must be consistent.
Set HSRP preemption in port setting status
Standby group number preempt
This setting allows other routers in the hsrp group to be the primary router. This option should be set for all routers so that each router can become a backup router for other routers. If this option is not set, the weight of the vro。 is higher than that of the primary router.
Set the hsrp weight of the vro
Standby group number priority weight
If this item is not set, the default weight is 100, and the weight number is large, the priority of preemptible master router is higher.
Set the hsrp group router authentication string
Standby group number authentication string
This option is optional. If this option is set, all vrouters In the hsrp group must perform this option, and only vrouters in the group with the same string can perform hsrp.
Set the hsrp switching time
Standby group number time parameter 1 time parameter 2
The Time Parameter 1 indicates how long the router exchanges the hello message at each interval to indicate whether the router is faulty or working properly. The Time Parameter 2 indicates the time in which other routers in the same group did not receive the information of the primary router, and the primary router is declared paralyzed. The default values are 3 seconds and 10 seconds respectively. If you want to change the default value, all the vrouters In the hsrp group must have the same settings.
Port tracking settings
Standby group number track port number
This option is optional.
This setting indicates that if the monitored port fails, the router is also switched. Multiple external ports can be tracked.
NOTE: If multiple lines are tracked on the primary router, when one line fails, it will switch to the backup router, even if everything else works normally, the route can only be resold after the primary router works normally. This setting can be fully implemented by the line backup function in practical applications. In most cases, this setting does not make much sense.
In addition, hsrp has many other settings and applications. For more information, see the Cisco site or Cisco Document or contact the Technical Support Center.

Instance: vro backup between 2511-1 and 2511-2