3com S7906E 설치 설명서

 

1-4 

A router in a VRRP group works in one of the following two modes: 

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Non-preemptive mode 

When a router in the VRRP group becomes the master, it stays as the master as long as it operates 

normally, even if a backup is assigned a higher priority later. 

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Preemptive mode 

When a backup finds its priority higher than that of the master, the backup sends VRRP advertisements 

to start a new master election in the VRRP group and becomes the master. Accordingly, the original 

master becomes a backup. 

To avoid being attacked by unauthorized users, VRRP authenticates the received packets by adding 

authentication keys into the packets. VRRP provides two authentication modes: 

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simple: Simple text authentication 

A router sending a packet fills an authentication key into the packet, and the router receiving the packet 

compares its local authentication key with that of the received packet. If the two authentication keys are 

the same, the received VRRP packet is considered real and valid; otherwise, the received packet is 

considered invalid. 

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md5: MD5 authentication 

The router computes the digest of a packet to be sent using the authentication key and MD5 algorithm 

and saves the result in the authentication header. The router receiving the packet performs the same 

operation using the authentication key and MD5 algorithm, and compares the result with the content in 

the authentication header. If the results are the same, the router receiving the packet considers the 

packet an authentic and valid VRRP packet; otherwise, the router considers the packet invalid. 

On a secure network, you do not need to set the authentication mode. 

VRRP timers include VRRP advertisement interval timer and VRRP preemption delay timer. 

The master in a VRRP group sends VRRP advertisements periodically to inform the other routers in the 

VRRP group that it operates properly. 

You can adjust the interval for sending VRRP advertisements by setting the VRRP advertisement 

interval timer. If a backup receives no advertisements in a period three times the interval, the backup 

regards itself as the master and sends VRRP advertisements to start a new master election.  

To avoid members in a VRRP group from changing their states frequently and make backups have 

enough time to collect information (such as routing information), each backup waits for a period of time 

(the preemption delay time) after it receives an advertisement with the priority lower than the local 

priority, then sends VRRP advertisements to start a new master election in the VRRP group and finally 

becomes the master.