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Conference netcad::hub_mgnt

Title:DEChub/HUBwatch/PROBEwatch CONFERENCE
Notice:Firmware -2, Doc -3, Power -4, HW kits -5, firm load -6&7
Moderator:NETCAD::COLELLADT
Created:Wed Nov 13 1991
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:4455
Total number of notes:16761

2163.0. "DECbridge-90 in parallel???" by BRUNEL::PADDICK () Tue Apr 04 1995 07:15

    
    
    Could you answer a quick question for me?
    
    Provided node numbers are within the "workgroup" limit, is it
    permissable to connect DECbridge-90's in parallel. As far as I can 
    see, they do run full spanning tree, and should therefore be able 
    to handle this OK.
    
    The DECbridge-90 spec states that it is and "endsystem" bridge, but
    I have read in this conference and elsewhere, that this isn't strictly
    true?
    
    The customer wants to have two hubs connected with two fibre-optic 
    links running across different parts of the plant for resilience.
    I have discussed with him a DECrepeater-90FL in one DEChub-900, and
    two DECbridge-90FL in the second DEChub-900.
    
    
    Thank ewe in advance,
    
    Meic Paddick - MCS Bristol UK.
     
    
    PS. I asked the Open DEC Connect designer tool to draw this network, 
        and it saw a loop and deleted one of the links.
T.RTitleUserPersonal
Name		DateLines
2163.1Reason for not putting DECbridge 90's in parallel...NETCAD::BATTERSBYTue Apr 04 1995 10:3513
    If two DECbridge 90 units are connected in parallel between a workgroup
    and a backbone, the spanning tree algorithm will only allow one bridge
    to forward packets at a time. This is fine as long as everything is
    working fine on both sides of the DECbridge 90's. But, if a failure occurs
    in the backbone segment, that results in the backbone LAN being broken
    into two separate LANs, the spanning tree may reconfigure such that all
    backbone traffic will be passed through to the work group. When this 
    happens, the workgroup side of the bridge may see more than 200 nodes 
    and enter flood mode.
    This is why it is suggested that one not put DECbridge 90's in parallel
    between a wrokgroup and a backbone LAN.
    
    Bob
2163.2NPSS::JOHNSONMike J., Network Products SupportTue Apr 04 1995 13:1126
We are currently working a CLD for major European customer regarding redundant
DB90's.  What I am finding is confusing at best.

   1).	Prior to "version 2" hardware and V3.1 of the Flash code, parallel
	bridges was ABSOLUTELY forbidden.

   2).	Version 2 hardware (all DB90FL's and DB90's with version 2.* ROM
	code) added Flood mode, and the concurrent release of V3.1 Flash
	enhanced the spanning tree code.

   3).	The user guides were then changed to contain text saying that parallel
	DB90's are OK, but the pictorial still shows it as forbidden.


As we work the CLD we will get more data, but the sour taste in my stomach tells
me:

   1).  Don't try it with Version 1 DB90 hardware, primarily because they
	don't do flood mode.

   2).	Don't recommend it if the condition described by Bob in 2163.1 
	might happen.

   3).	There are problems or else I wouldn't be looking at a CLD.

/mj