Transcript Routers, Switches, and Hubs

Routers, Switches, and
Hubs

Networkin
g devices
must be
able to
accept an
ARP
update
after a
group
failover.

A server cluster installation requires hardware compatible routers, switches,
and hubs. For the client to respond to a failed virtual server, Microsoft Cluster
service sends a gratuitous Address Resolution Protocol (ARP) update to the
network devices. The ARP update notifies the client of the new media access
control (MAC) to IP address association. The clients can then redirect client to
virtual server communication to the new controlling node.

You need to verify that hubs and switches can forward the ARP update to
clients and routers. However, some devices, such as switches, may not
forward the gratuitous ARP request to other devices. Hubs will always forward
ARP updates. A switch may not forward the update, but you can configure it to
forward the updates. A router never forwards the update, however it needs to
be able to accept the update and change its ARP table. It is important to
choose and test routers and switches for compatibility prior to implementation
of a server cluster.

In this example, Node A is controlling \\Accounting with an IP address of
10.0.0.5. The clients and routers contain an address table of the IP to MAC
relationships. When the virtual server changes ownership, Node B sends out a
gratuitous ARP update to the local subnet. Hubs and switches forward the
information to clients and routers on the local subnet. Routers contain an IP to
MAC address table on behalf of clients on remote subnets, therefore routers
do not forward the information but must be able to accept the ARP update.