|
Lesson 2
Using Network Load Balancing
7-19
NLB server duties. There are also no problems with routers handling
multicast MAC
addresses and no bottlenecks caused by cluster traffic and ordinary network
traffic
sharing a single network interface adapter.
NLB Networking
Although the servers in a Network Load Balancing cluster do not share a
single data
store, as in a server cluster, and perform their own independent
calculations to deter-
mine which server will service an incoming request, the servers do
communicate with
each other. The cluster servers must exchange information to know many
servers are
in the cluster, and to determine when a server has been added or removed
from the
cluster. This communication enables the cluster to compensate for a failed
server and
to take advantage of new servers in the cluster by redistributing the
traffic load.
Important
A single computer running Windows Server 2003 cannot be a member of a Net-
work Load Balancing cluster and a server cluster at the same time, because
these two clustering
solutions use network interface adapters in different ways. If you want to
deploy both an NLB
cluster and a server cluster on your network, you must use separate servers
for each cluster.
The cluster traffic between NLB servers takes the form of a heartbeat
message that each
server transmits once per second to the other servers in the cluster. If one
cluster server
fails, it stops transmitting its heartbeat messages, and the other servers
detect the
absence of the heartbeats. Once the other servers in the cluster miss five
consecutive
heartbeat messages from a server, they begin a process called convergence,
in which
they recalculate their traffic distribution algorithm to compensate for the
missing server.
In the same way, adding a new server to an NLB cluster introduces a new
heartbeat to
the network, which triggers a convergence in the other servers, enabling
them to redis-
tribute the traffic so that the new server receives an equal share of the
load.
Note
Because all the servers in the cluster are using the same cluster MAC
address, trans-
mitting the heartbeats is simply a matter of directing the packets to that
address. The serv-
ers don’t need to broadcast the heartbeat messages, reducing the impact of
the cluster
traffic on the network.
When you deploy NLB cluster servers with a single network interface adapter
in each
computer, obviously all the cluster-related traffic must travel over the
same network as
your ordinary traffic. This is usually not a major burden, because the
heartbeat packets
are small, less than 1,500 bytes, so they fit into a single Ethernet packet.
If you decide
to install multiple network interface adapters in each cluster server, you
can connect
both adapters to the same local area network (LAN) or construct a separate
network for
the cluster traffic.
|
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)
.png)