cisco 500-651 certification

cisco 500-651 certification.To modify the Hello time and Hold time, execute the following standby command.Switch(config-if)# standby [group_#] timers hello_time holddown_timeThe range of possible values for hellotime is 0.255 seconds, and the default is 3 seconds; the range of possible values for holddown time is also 0.255, but the default is 10 seconds. Note that the holddown_time should be at least 3 times the hello_time to ensure proper operation of HSRP.Exam Point The HSRPHello timer defaults to 3 seconds and the failure timer defaults to 10 seconds. A common practice is to make these timers shorter to increase the convergence speed of HSRP. However, never set them too short or they may result in unexpected switching. To configure authentication, execute the following standby command on the interface. Router(config-if)# standby [group-number] authentication passwordThe password is a maximum of 8 characters and defaults to cisco if omitted. the password configured on all routers in the same HSRP group must be the same.Interface TrackingIn some cases, it may be necessary to enable the active routing device to resign, giving up this role to another routing device. See the example shown in Figure 18.4, where RP-B is the active RPO for VLAN 20 If RP-B goes out of service, RP-A will not receive a Hello message from RP-B and thus discover this. RP-A will promote itself and start forwarding frames sent to the virtual MAC address.However, suppose that RP-B itself does not fail, but only interface vlan40 (which is connected to the core layer) fails, as Figure18.5 shows. If HSRP is not running,RP-B will detect this failure and in turn send an ICMP redirect message to RP.This will allow RP-A to handle the traffic after redirection. However, if both RP.A and RP.B are participating in the HSRP group, ICMP redirection will be disabled. This means that RP.B still acts as the active routing device for all traffic sent to the virtual MAC address. The problem this causes is that after the Layer 3 routing protocol converges, these flows are still able to reach their destination, but in order to get to their destination, they must go through RP-B and RP-A, which adds unnecessary delay.