Conference netcad::hub_mgnt

    It defaults to 802.1d, but also supports Digital LB100 mode, and
    so also supports automatic detection of LB100 and switchover to
    the appropriate STP. I think a means of locking it in 802.1d if
    necessary is provided through HUBwatch. The fact that it supports
    both modes though, means it will autoselect without needing HUBwatch.
    
    Bob

To set the default spanning tree mode, you need either HUBwatch or any
SNMP management tool.  The MIB variable is ebrLB100SpanningTreeCompat
from the DEC elanext MIB.  autoSelect(1) lets the bridge decide. ieee802(2)
locks it into 802 mode.

Tom Hood
HUBwatch

    Thanks for the replies.
    
    Just to clarify. If I purchase a Decbridge 900, by default it should
    come up set to autoselect (Running 802.1d spanning tree but capable of
    switching to lanbridge 100 if it sees Lan bridge 100 hellos).
    
    If I want to, I can lock the bridge into 802.1d with management
    software.
    
    Is this correct?
    
    Thanks,
    
    Jon
    
    P.S. Does anyone know what the default root priority and associated
    cost is for the decbridge 900?
                    

    Hi Jon, you're correct. The DECbridge 900MX defaults to autoselect
    and defaults to 802.1d STP, and you can lock it down in 802.1d if
    you choose. I would suggest that you do not do this, unless you
    absolutely have to though. You don't want to have more than one
    spanning tree topology running amuck in your LAN, it could raise
    havoc in your LAN.
    On the parameters you asked about, I do recall that the typical values
    used for other DEC bridges which support 802.1d, the root priority
    usually defaults to 128, the "Port cost" defaults to a value of 10, 
    and the "Root path cost" defaults to a value of 40. I don't recall
    whether the DB900MX values are exactly the same as these though.
    
    Bob

    BTW the Root Priority and Root Path cost are defined by the
    Root bridge in your extended LAN, and all other bridges use
    these values.
    
    Bob

    Thanks for the quick response,
    
    
    Well, I've just managed to get hold of a DECbridge900 and checked what
    the defaults are. As far as I can see the default setting for the bridge is
    IEEE 802 - You can change this to autoselect if required from within
    Hubwatch.
    
    I tested this by selecting autoselect from within Hubwatch and then
    doing a factory reset - it was reset to IEEE 802.
    
    This seems to be the opposite from what was said earlier and I must
    admit does appear to be the wrong way round.
    
    Any comments anyone ?
    
    
    Jon

    I goofed, I meant that the default *is* 802.1d as you observed,
    and as you also correctly observed, autoselect can be selected
    from HUBwatch.
    
    Bob

    re .7
    
    Sanity check:
    
    What you're saying is the DB900MX does not come up in autoselect
    mode and we need to be aware that this will cause problems on
    customer's networks that consist of bridges running in LB200 mode. 
    Correct?
    
    Bill
    
    
    

    That's absolutely correct. If your customer has *any* bridges
    running LB100 STP, if you don't set the DB900MX (using HUBwatch),
    to Autoselect, there could possibly be more than one STP topology 
    on you customers extended LAN. The LB200's default to 802.1d *with*
    autoselect enabled. So in a network with no LB100's they would behave
    fine with the DB900MX. The problem is older DEC bridges like the LB100
    which are a true epoch 1 bridge. Other vendors also have bridges which
    only configure as LB100 - like spanning tree. Other vendors also have
    bridges which *won't* handle LB100 STP at all, only 802.1d STP. So the
    bottom line is to be aware of what your customer has for other LAN 
    hardware so you can best advise them as to how to set up their LAN for
    maximum connectivity, flexibility, and managebility.
    It's not that the DB900MX won't default to autoselect that will cause
    problems, it's that there is older generation Ethernet hardware still
    being used by customers which is the hassle.
    
    Bob

    
    The problem with having the bridge autoselect, and part of the reason
    why the default is to be locked to 802.1d is that (at least) the Cisco
    implementation of the compatibility mode is broken in such a way that
    it will cause all auto-select bridges to toggle back and forth between
    modes every couple of minutes.  This creates a very unstable situation
    that is difficult to debug unless you've seen it before.
    
    Be aware that the DECbrouter 90 uses Cisco code, and has this problem.
    
    Here in Networks Engineering, we run our LAN with all production
    bridges locked to 802.1d.

    > Here in Networks Engineering, we run our LAN with all production
    > bridges locked to 802.1d.
        
    That's true but our extended LAN was re-built and converted to
    an FDDI LAN, and all the LB100's were retired-to-that-great-LAN
    -in-the-sky.
    I will still maintain however, that .0 still has to be cognizant of 
    what his customer has for equipment in their LAN and make suggestions
    on how best to configure it. *If* his customer has a very large # of 
    old DEC LB100's, and doesn't want to get rid of them then our newer
    products have to be able to be backwards compatible. That was my 
    point in discussing autoselect. Having more than one spanning tree
    is also something that *should* be avoided if at all possible.
    
    Bob