Has anyone found a way to use Symantec Ghost over a wireless connection,
specifically when trying to image a computer or group of computers? We
use Ghost very reliably on our wired systems, but we have a few labs
with wireless-only computers and it is a lot of extra time and effort to
image them. We're wanting to multicast, not unicast or directed
broadcast. To date, our problem seems to be the lack of a DOS driver
for the wireless NIC.
Chris Gauthier, CCNA, Network+, A+
Network Administration Team
Portland Community College
Portland, Oregon
"For once you have tasted flight you will walk the earth with your eyes turned
skywards, for there you have been and there you will long to return."
--Leonardo da Vinci
Kevin Miller wrote:
There seems to be a lot of interest in this topic... some of my
thoughts...
We have a couple of wireless multicast applications that have been
tested. One is intended for classroom use, and the minimum acceptable
performance was 0 packet loss, 100% of the time. (Unfortunately, these
requirements are, not surprisingly, much clearer in hindsight than in
planning.) The other is multicast IP/TV, where some packet loss is much
more tolerable.
Along the way there have been bumps with the infrastructure; multicast
was/is not supported in a WLAN Override environment, as we were
originally running. (WLAN Override is the Cisco way to apply a different
vlan to a shared SSID, as we did for geographically separate areas.)
Another bump was the issue related to rogue AP suppression in
multi-controller environments. (As I griped to this list awhile back,
this is one of a few reasons that, on balance, I advocate not using
rogue AP suppression.)
FWIW, in our case the APs are all layer 3, and we therefore enabled PIM
on the AP networks to deliver that traffic from the controller.
At this point, I believe the delivery of multicast from the controllers
to APs (and back) is solid in our environment. But we still have the RF
environment and 802.11 protocol to contend with.
While I've not directly observed problems related to the usual multicast
802.11 concerns (slowest transmit rate and other trade-offs to
compensate for the shared RF environment), interference continues to be
an issue in achieving 100% reliable multicast delivery. Unfortunate for
our classroom use case is the fact that the academic building houses
wireless researchers, has dense AP coverage, and we're talking about a
decent (e.g. 20) number of multicast clients.
Thus, at this point I am very concerned about application approaches to
using multicast versus the robustness of wireless networking. Because
the classroom application in our case had no reliable mechanism for
retransmitting lost frames (or even identifying them), the loss of a few
packets was not tolerable. Some days and times it works flawlessly, but
other times it's unusable.
On the other hand, the IP/TV streams generally work well. Our test case
was also the environment where we first disabled the lower connection
rates to force greater transmit rates. A few dropped frames may be
observed but are quickly obsolete.
We continue to have multicast enabled and running throughout the
wireless network. I would recommend taking a hard look at applications
and making sure everyone agrees as to expectations. We are continuing to
improve our sophistication as it relates to RF/802.11 analysis, and are
aiming to use active monitoring agents to provide more continuous
analysis of critical spaces.
I would be very interested in hearing of other experiences or thoughts
along these lines.
thanks,
-Kevin
Kevin Miller wrote:
We've done some work with wireless multicast. Would be willing to share
off-list. A few horror stories, unfortunately.
-Kevin
Lee H Badman wrote:
Any wireless multicast experts in the group that might be willing to
field some questions outside of the group?
Thanks-
Lee H. Badman
Wireless/Network Engineer
Information Technology and Services
Syracuse University
315 443-3003
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