Notes about automatic relay assignment

The BigFix clients use a sophisticated algorithm to calculate which relay is the closest on the network. The algorithm uses small ICMP packets with varying TTLs to discover and assign the most optimal relay. If multiple optimal relays are found, the algorithm automatically balances the load. If a relay goes down, the clients perform an auto-failover. This represents a major improvement over manually specifying and optimizing relays. However, there are a few important notes about automatic relay selection:

• ICMP must be open between the client and the relay. If the client cannot send ICMP messages to the relays, it is unable to find the optimal relay (in this case it uses the failover relay if specified or picks a random relay).
• Sometimes fewer network hops are not a good indication of higher bandwidth. In these cases, relay auto-selection might not work correctly. For example, a datacenter might have a relay on the same high-speed LAN as the clients, but a relay in a remote office with a slow WAN link is fewer hops away. In a case like this, manually assign the clients to the appropriate optimal relays.
• Relays use the DNS name that the operating system reports. This name must be resolvable by all clients otherwise they will not find the relay. This DNS name can be overridden with an IP address or different name using a task in the Support site.
• Clients can report the distance to their corresponding relays. This information is valuable and should be monitored for changes. Computers that abruptly go from one hop to five, for example, might indicate a problem with their relays.
• More information about relays, automatic relay selection, and troubleshooting relays can be found at the IBM BigFix support site.