High Availability on Routers - HSRP, VRRP, GLBP

Question

I have two MLS Connected to a Layer 2 Switch, Behind Layer 2 Switch there are some 5 hosts are there.

MLS - A - Active Router IP Add - 192.168.1.10 MAC Add - 0000.aaaa.aaaa Priority - 200 VLAN 50

MLS - B Standby Router IP add - 192.1681.11 Mac Add - 0000.bbbb.bbbb Priority - 100 Vlan 50

Virtual IP address - 192.168.1.1 Virtual Mac Address - 0000.0c07.ac01

When MLS - A is down , Its going to send a Resign Message to MLS - B.

How come the Layer 2 Switch will come to know about MLS A got down and It needs to send the traffic to MLS- B Immediately.

Whether Once the switch got the Resign Message of MLS - A, Its going to Flush the MAC table and Relearn the MAC table completely. Please Let me know How its Possible for the Layer 2 Switch to switch the traffic immediately towards MLS - B

Answer 1

It's all about the timers. There's an advertise interval and a master down interval (hello and hold time in HSRP and GLBP). The master sends VRRP advertisements according to the advertise interval. This lets the backup know that the master is up. If the backup doesn't receive an advertisement within the master down interval, it will transition to master. The key to keeping connections alive is tuning your intervals down to sub-second failover.

When the backup router takes over, it sends a gratuitous ARP message telling everyone to use its MAC address for the virtual IP.