| This Note from the Ethernet conference should answer your questions
on flood mode.
Phil
<<< UPSAR::USER$411:[NOTES$LIBRARY]ETHERNET.NOTE;1 >>>
-< Ethernet Volume 3 >-
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Note 61.6 Bridge 90 new Version 6 of 14
PRNSYS::LOMICKAJ "Jeffrey A. Lomicka" 76 lines 3-DEC-1992 11:12
-< New DECbridge-90 features >-
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> - what will be offered functionally in the hardware upgrade, i.e.-
> what exactly is the controversial "Flood Mode" all about, please?
When you have a DECbridge-90 that contains the new gate array and boot
ROM (All DEWGF's and those DEWGB's which have boot ROM is version 2),
you get:
- More counters (the ones that were missing from the first
revision because of gate array problems).
- Flood mode.
When "flood mode" is enabled, backbone traffic is forwarded to the work
group without regard to what is in the learned address database.
Protocol filters are still effective, but the address table is ignored.
This ensures that a station in the work group will have full
connectivity to both sides of the network, even if its address is not
in the address table.
This would be used in the following cases:
- If there are more than 200 stations in the work group, so they
don't all fit in the table.
- If there is a station in the work group that does not
transmit, so it is never learned, and you need to transmit
messages to it from the backbone.
Flood mode comes on automatically if you exceed 200 stations in the work
group. You can also enable it from the management console to force it
to be enabled when there are less than 200 stations in the work group.
(If there are more than 200 stations in the work group, you cannot
disable it.)
The implications of this are as follows:
- A DECbridge-90 can be used as a backbone bridge when desired
to match incompatible media or extend the physical length and/or
repeater count. (the most obvious case being 10BaseF fiber to a
hub full of repeaters).
- A DECbridge-90 can be used as a backbone bridge to provide
protocol isolation using the protocol type filters. (An obvious
case would be to divert IP or Appletalk traffic through a
parallel router.)
- However, when used with flood mode enabled, a DECbridge-90
does NOT do much to help your traffic situation, because the
only traffic filtering it will do is what you set up in the
protocol filters.�
> - where can DENMA docs. be obtained?
I don't know. The product manager is Jack Forrest.
> - what does the DEWGF fiber interface connect TO? (do we have a
> compatible 10BaseF device?)
The DEChub-90 series 10BaseF repeaters that were annouced the
same time as the fiber bridge (DECrepeater-90FA and
DECrepeater-90FL), another fiber bridge (DEWGF), the just
announced 10BaseF "DESTA" (I don't know the real name), or
presumably to any other 10BaseF compatible device. I don't
know if that includes the LB200 or not.
______________
�Okay, one technicality is that messages from the work group that are
addressed to a station whose address is one of the lucky 200 to be in
the work group table, are not forwarded to the backbone, so it is not
strictly true to say "address filtering is disabled and everything is
forwarded". Some of the work group to work group traffic is still
isolated to the work group. However, since you can't predict WHICH 200
stations will be learned into the table, you should not count on this
fact to provide any real reduction in total traffic.
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