Hi, I have this situation:
A client of mine has a switched network. On that network where no vlan is configured, he has multiple IP address on the same vlan (vlan 1). So, I´ve installed a 5505 with two vlans, and asigned each vlan to ethernet interfaces. I´ve made 2 connections, from switch to each ASA interface. The problem is when I execute show arp on the ASA, I receive the same entry on both interfaces.
I hope in first place that you understand my english, and in second place you can help me :-)
The ARP table will be built based on the ASA seeing ARP broadcasts and replies. If the client has one VLAN (= one broadcast domain) then both interfaces will see all of that traffic and build identical ARP tables.
The correct way to change this would be to create a second VLAN for the second set of IP addresses and assign the appropriate interfaces (including the second ASA client-facing interface) to that VLAN.