3. Creating a Multicast Deployment
You now know some of the theory behind a WDS client.
It is time to see how to put this theory to use. We will look at
setting up the behavior of multicast on the WDS server. You can do this
by editing options on the Multicast tab in the properties of the WDS
server in the WDS console, shown in Figure 3.
Here you can configure how IPv4 or IPv6 addresses
are assigned to WDS multicast clients. By default, the WDS server will
manage a predefined range of IP addresses (select the Use Addresses
From The Following Range radio button). You need to ensure that there
is no IP range overlap between servers if more than one WDS server can
service a subnet or subnets. You can choose to allow DHCP to manage the
allocation of IP addresses (select the Obtain IP Address From DHCP
radio button).
The Transfer Settings area allows you to manage how
WDS multicast will deal with clients with different network connection
speeds. You have four options here:
The default, keep all clients in a single multicast session at the same speed
Divide clients into slow, medium, and fast sessions
Divide clients into slow and fast sessions
Automatically disconnect WDS clients that have a connection speed that is less than defined (in Kbps)
You will choose one of the Transfer Settings options
based on how many client network speeds you have and how many
simultaneous streams you want. For example, if you have 100 Mbps and 1
Gbps clients, then will want to support slow and fast sessions. If you
add additional clients with 10 Gbps network cards, you might want to
support slow, medium, and fast sessions.
You need to create a multicast transmission in the
WDS console (under Multicast Transmissions) and associate it with an
installation image if you want to perform multicast deployments. Any
WDS client requesting that installation image will then initiate or
join a multicast session. You can create a multicast transmission by
right-clicking and selecting Create Multicast Transmission.
The Create Multicast Transmission wizard will
appear. The first screen asks you to name the transmission. Provide a
meaningful name that will make sense to you and others at a later time.
The Image Selection screen allows you to associate
an installation image with the multicast transmission. You can navigate
between image groups and select the installation image that you want to
deploy via multicast.
Figure 4
shows the Multicast Type screen. On this screen you can switch between
the default Auto-Cast option (where the multicast starts as soon as any
WDS client requests it) or the Scheduled-Cast option. The
Scheduled-Cast option allows you to control the start of a multicast.
In this way, you can make the most of multicast functionality and
available bandwidth. By default, if you select Scheduled-Cast, WDS
clients will join the multicast but nothing will happen until an
administrator approves starts the session. There are two suboptions for
Scheduled-Cast that allow the session to start automatically.
Start When The Number Of Clients That Have Requested The Image Is
This option allows an administrator to set a
threshold. A minimum number of WDS clients must join the multicast
before it starts.
Start At A Later Time
WDS administrators can define a date and time when the multicast session can start.
You can choose to not select any Scheduled-Cast suboptions, select one at a time, or combine them as required.
The new multicast transmission will appear in the
WDS console under Multicast Transmissions. It will have a status of
Waiting while no WDS clients are connected to it.
Note that you cannot edit the properties of a
multicast transmission. You will have to delete it and re-create it if
you want to make any changes. You can have more than one multicast
transmission, thus providing support for different installation images.
Now you can boot up your WDS clients. Log into the
WDS client and select the image that is associated with the new
multicast transmission. If you selected the Scheduled-Cast option, the
image download will not start right away. Instead, you will be told
that the WDS client is waiting for the server, as shown in Figure 5.
Back in the WDS console, you can navigate into your
new multicast transmission object to see which WDS clients are
connected (you might need to refresh the screen). Here you have a few
options. You can instruct a WDS client to bypass multicast and start a
normal download. You can also disconnect the client to abort the image
download.
You can right-click on a multicast transmission to
manually start the session. You can do so even if the transmission has
not yet met any defined start conditions.
The multicast session will appear as Active once it
starts. The detail for each WDS client's session can be seen within the
multicast transmission object. Here you get information that can be
used to monitor progress and troubleshoot the multicast transmission:
Identifying information (MAC address and IP address)
Image download progress (Status)
The amount of time that the WDS client has been connected to the multicast transmission
Data transfer rate
WDS client CPU utilization
The image will be expanded and installed once it is downloaded to the clients.
4. Troubleshooting a Multicast Deployment
Two problems can commonly occur with a multicast deployment.
4.1. Slow Multicast Image Download
The most common complaint will be that a multicast
transmission is very slow. You should use the multicast transmission
client information in the WDS console. Doing so gives you a quick
overview of what is happening.
The most obvious thing to do is to check the
network. Things like dodgy switch ports or other network activity could
affect the speed of an image download. Microsoft recommends that you
use switches instead of hubs, and that you use CAT5 or CAT5e cabling or
better. Check with your network administrator colleagues or the network
monitoring systems to see if anything stands out.
You may have a mix of clients with different
connection speeds. If so, make sure that you have set up the multicast
configuration (WDS server properties) to divide up the transmission
into slow/fast or slow/medium/fast sessions.
Sometimes a single faulty machine can cause a large
multicast to run slowly. This machine will have a slow connection and
will become the master client, thus reducing the download for everyone
else in its session. You can identify the master client by running this
command:
Wdsutil /Get-AllMulticastTransmissions /ShowiInstall /DetailsiClients
This code will return information on each of the clients. Search for an attribute called Master Client where the value is set to Yes. This is the machine that is causing the session to be slow. Note the ClientID
value for this machine. This value is what you will use to identify the
machine. You can disconnect this machine in the console or by running
this command:
Wdsutil /Disconnect-Client /ClientID:<ClientID of the master client>
The role of master client will switch to the next
slowest machine. Check the download rates to see if they have improved.
If not, you will need to identify and disconnect the new master client.
4.2. Network Flooding with IGMP Snooping Disabled
Without IGMP snooping enabled on network devices,
the multicast will effectively become a broadcast and can flood the
network. The obvious answer would be to enable IGMP snooping. This
might not be possible. If that is the case, you can limit the life of
the multicast packets on the network using a Registry edit on the WDS
server. Microsoft suggests that you set the time-to-live (TTL) for the
multicast packets to 32. On Windows Server 2008 you do so by editing HKEY_ LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\WDSServer\Providers\Multicast\ Profiles. On Windows Server 2008 R2, you do so by editing HKEY_LOCAL_MACHINE\System\ CurrentControlSet\Services\WDSServer\Providers\WDSMC\Protocol.
