A Practical Cisco router backup method is introduced.

There are many things involved in Cisco router backup. There are also a variety of backup technical methods, so there will be a bit of confusion in the selection of methods, the following shows you a way. 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
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, it continues to send Proxy ARP broadcasts. The Cisco router backs up the requests and transmits 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 communicating can find the Cisco router backup for transmission only after another Proxy ARP request or restart. Cisco routers support Proxy ARP

IRDP: computers that support IRDP in the LAN will listen to the "Hello" Multicast information packet sent by the master router. If the computer no longer receives the "Hello" message, it uses the backup router for data transmission. Dynamic Routing. For some computers, they support RIP dynamic routing to find routers. The disadvantage of this method is that the conversion between the master router and the backup router is slow.

The above three methods are mainly used on the computer side. Cisco router Backup 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 such information packets for a period of time.

Other backup routers will think that the router is broken. The backup of a Cisco router with a high weight power takes over the virtual MAC address and IP address, and is 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:

1. Under port configuration, set the port IP address, ip address port IP address Subnet Mask

2. in port configuration, enable the HSRP function, 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, the virtual addresses of all vrouters in the same hsrp group must be consistent.

3. Set HSRP to seize the standby group number preempt in the port setting status. This setting allows other routers in the hsrp group to become the master router. This option should be set for all routers so that each router can be backed up by other Cisco routers. If this option is not set, the weight of the vro。 is higher than that of the primary router.

4. Set the hsrp weight of the vro standby group number priority. If this parameter is not set, the default weight is 100. If the weight is large, the priority of the master router is higher.

5. sets the authentication string of the standby group number for the hsrp group vro identity authentication. this parameter is optional. If this parameter is set, all vrouters In the hsrp group must perform this setting, hsrp can only be performed on vrouters with the same string.

6. set the hsrp switching time. The standby group number time parameter 1 time parameter 2. The time parameter 1 indicates the time at which the router switches the hello Message for 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.

7. Port tracking settings: the standby group number track port number. This setting 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.

2511-1 and 2511-2 are mutually backed up by Cisco routers,
2511-1 configuration, 2511-1 # sho run
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