I'm trying CARP load balancing on several switchs and most have behavior not compatible with CARP balancing both in ip and ip-stealth mode. Ip-unicast also seem a bad option in my test since all switch I tested that support mirroring can only mirror to one port (or I didn't see any option to mirror to multiple ports).
List of tested switch: Netonix WS12-250A (manage but a lot less options than HP since it's a new player) HP Procurve 2530-24G (full manage) HP 1700-24 (smarth) D-Link DGS-1016D (unmanage) Mikrotik RB750UP (Router with WAN + 4 ports switchs with management fonctionnality) In IP mode, with most tested switchs, both carp hosts will be master on both groups so carp advertisement are drop by the switch but if I ping the carp adresse from my PC, If I ping the CARP ip address, I get duplicate echo return so icmp pass through while carp advertisement are dropped. The only exception was a Mikrotik RB750UP with my PC and the 2 CARP hosts connected on the switch side. It was letting carp advertisement pass and carp load balancing seem to work fine with this device even if I would not use this for a big setup. Maybe I will try one of their switch like cloud core switch series that use the same OS (RouterOS). In IP stealth mode, with most tested switch, the state of the CARP interface are fine and seem to work as expected but the with tcpdump listening on the physical interface I only see the icmp request hit one CARP host at time so the switch will only send traffic to one of the CARP host randomly instead of broadcasting it on every port like writen on the CARP doc or FAQ. The only exception to this was the HP 1700 that will also not pass any traffic in this mode. On port stats, I saw stat multicast increase in both tx and rx (rx only in IP mode) but can't ping the carp interface IP address from my PC. On the HP 2530 that is full manage and support more option than the other managed switchs, I've done more test. I tryed with IGMP disabled, like recommended on pfsense carp doc in the "Switch/Layer 2 Issues" section https://doc.pfsense.org/index.php/CARP_Configuration_Troubleshooting#Switch.2FLayer_2_Issues I also tryed with igmp enabled and all ports paquet control policy at forward. Looking at HP documentation about multicast, it seem like igmp is the only option to control multicast. I looked at 2 HP document without finding any other options to limit multicast. So fare, I only had only succes with Mikrotik in ip mode. Did somebody have been successful with other switchs ? I know most use CARP only on fail over and recommend to have 2 gateways that can support full load but I think it would be interessting to have a cluster of less powerfull gateway (number needed for the load +1). It could save a lot of power and we can find small PC that cost a lot less that the price of Xeon. I think it would also be easier to adjust the number of hosts on a cluster as the traffic increase than change the gateways for more powerfull ones.
