Multi-homed hosts

Hosts that have more than one network interface usually have one Internet Protocol (IP) address for each interface. Such hosts are called multi-homed hosts.

EGO identifies hosts by their official host name, so it needs to match each of the network addresses of multi-homed hosts with a single host name. To do this, the host name information must be configured so that all of the Internet addresses for a host resolve to the same name.

Multiple network interfaces

Some system manufacturers recommend that each network interface, and therefore, each Internet address, be assigned a different host name. Each interface can then be directly accessed by name. This setup is often used to make sure NFS requests go to the nearest network interface on the file server, rather than going through a router to some other interface. Configuring this way can confuse EGO, because there is no way to determine that the two different names (or addresses) mean the same host.

All host naming systems can be configured so that host address lookups always return the same name, while still allowing access to network interfaces by different names. Each host has an official name and a number of aliases, which are other names for the same host. By configuring all interfaces with the same official name but different aliases, you can refer to each interface by a different alias name while still providing a single official name for the host.

IP connectivity

Some or all hosts have multiple network interfaces that connect to physically segmented networks. You may not want EGO to use the first IP address according to DNS to initiate a connection.

IP preference

A host has multiple network interfaces that connect to physically connected networks, but for routing or performance reasons, you might want to assign network interface preferences to different activities.

For example, communication between a Platform Symphony client and management hosts could use one network interface, and communication between a Platform Symphony compute and management hosts could use another network interface. While it might be physically possible for a socket client to use the first IP address of a socket server according to DNS to initiate a connection, this might not be desirable.

Host name lookup

A common DNS server may return a different IP address in host name lookups depending on which subnet that host is on (different BIND/DNS views). For example, host named hostA might resolve to 192.168.0.1 on one subnet and 10.0.0.1 on another subnet on the same network.

Filtering a preferred IP address from multiple IP addresses

Use EGO_PREFERRED_IP_MASK in ego.conf to specify the preferred IP address for multiple network interfaces.

If more than one IP address matches the IP mask, the first matching IP address is used as the preferred IP address. If no addresses match the mask, the order of the address list is not changed.

Under some circumstances (when you have multiple aliases), you also need to specify the unique official name and list the aliases.

IP mask format

Specify the IP mask as conventional CIDR blocks, consisting of a four-part dotted-decimal address, followed by a slash, then a number from 0 to 32:

nnn.nnn.nnn.nnn/nn