Well I should have asked question different way. I have config for two pairs (one pair in one segment and another pair in another segment) and failover configuration is different in terms of one pair has two unique vlans being trunks across crossover cable - unique LAN failover vlan and state vlan while other pair only has one vlan for both purposes...

PAIR-1

failover

failover lan unit primary

failover lan interface failover Vlan100

failover polltime unit 15 holdtime 45

failover link failover Vlan100

failover interface ip failover 192.168.1.1 255.255.255.252 standby 192.168.1.2

PAIR-2

failover

failover lan unit primary

failover lan interface failover Vlan300

failover polltime unit 1 holdtime 3

failover polltime interface 3

failover interface-policy 1

failover link stateful Vlan301

failover interface ip failover 192.168.254.1 255.255.255.252 standby 192.168.254.2

failover interface ip stateful 192.168.254.5 255.255.255.252 standby 192.168.254.6

According Cisco's failover configuration document you should have two vlans trunked across two chassis (ASA or FWSMs on 6500s). I am trying to understand what type of traffic "lan interface failover" vlan 300 in above config and "link stateful" vlan 301 in above config carry across? What is the best practice? should have uniqe vlans or just one vlan for both purposes? Sorry for not being clear on my initial question.

Hello Atrey,

Well it is 100 % recommeded to use 2 different vlans ( FWSM) or 2 different interfaces (ASA) for the failover link and the state link between 2 units, this because of the amount of data being transfered on both of this links,

Not all the time you have the oportunity to use 2 of them so that is why you can use only one, I have seen a lot of scenarios using just one and that works perfect but again if possible then use 2

Is just a desing preference or optimization

Regards,

Julio