How can I configure 6509 switch to have a standby capabalities? How does it work? (show standby). Thanks.
You are talking about HSRP - read the below:-
show standby refers to the HSRP protocol that provides a Virtual default gateway on a vlan.
Using HSRP makes sense if you have two devices routers or multilayer switches (even of different models) that can be the exit point for clients in a vlan
on a C6500 the standby configuration is performed on L3 SVI Vlans
interface vlan 50
ip address 10.10.50.3 255.255.255.0
standby 50 ip 10.10.50.1
standby 50 preempt
standby 50 priority 105
standby 50 track vlan 10
this an example, default priority is 100 the highest priority router becomes active.
the VIP address is an address in the same IP subnet of the vlan interface
HSRP emulates VIP 10.10.50.1 at both L3 and L2 using a well known mac address that in the righmost byte has 0x32 = 50
On a multilayer switch you can reuse the same group number (50 in the example) on different SVI VLans but VIP address has to be given accordingly to vlan subnet
And again this is useful if you have multiple L3 devices serving the same subnet otherwise you are just preparing to install a second router/multilayer switch
Hope to help