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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

1915.0. "Redundant configuration with DECswitch900 EF ?" by ANTIK::JONSSON (Lars Jonsson) Fri Jan 20 1995 11:01

Hi,

Two Decnis and two DECbridge900MX are connected with an FDDI-ring.
How can I set up DB900MX A and B, so that DB900MX A port 3 and DB900MX B port 3,
goes into backup mode ? Presume DECnis A is the root bridge. 

Normally, both ports on DB900MX A goes into forwarding or ? They seem to be
closer to the root bridge.



		I---------------I      FDDI	I----------------I
		I DECnis A	I---------------I DECnis B	 I 
		I    	        I               I        	 I
		I---------------I		I----------------I
		   |	    			    	    |
		   |	    			    	    |
		   |	    			    	    |
		I---------------I      		I----------------I
		I DB900MX A	I---------------I DB900MX B	 I 
		I    	        I               I        	 I
		I---------------I		I----------------I
		   |2	   |3			   |2	   |3	
		   |	   |	    Ethernet	   |	   |	
		   |	 --|-----------------------|--	   |	
		   |	   	    Ethernet		   |	
		 --|---------------------------------------|--

	

Can I fix this by modifying "port cost" somewhere ?


Regards,
Lars
T.RTitleUserPersonal
Name		DateLines
1915.1Not possible to split the forwarding portsNETCAD::KRISHNATue Jan 24 1995 19:4053
    Hi,
      Let me redraw the config so that it is easier to explain :
    
    				I---------------I
    				I DECnis A	I 
    				I    	        I
    				I---------------I
                                        |
                                        |               FDDI LAN
    ---------------------------------------------------------------------
            |                           |                   |
            |                           |                   |
    I---------------I          I--------------I       I------------I
    I DECnis B	    I          I  DB900MX A   I       I  DB900MX B I
    I    	    I          I   2      3   I       I  2     3   I
    I---------------I          I--------------I       I------------I
                                   |      |              |     |
                                   |      |              |     |
                                   |      ----------------     |
                                   |                           |
                                   -----------------------------
     If you assume DECnis A as the root, the FDDI ports on DECnis B and
     DB900MX A and DB900MX B would be in forwarding, as they are the
    closest link to the root. 
    
    Now on the ethernet Lans, both bridges would advertise a cost of 4
    (default cost of FDDI link) to the root. In case of a tie, the Bridge
    Id breaks the tie. The bridge id is a 8 byte integer, consisting of the
    Bridge Priority (2 bytes, default value 128) and the 6 byte Mac address
    that is the Node id. If the priority field in the DB900MX's are left at
    the default value, the bridge with a lower mac address for the node id
    wins the tie. So the bridge that wins the tie will go into forwarding
    on both the ethernet Lans and the ports on the other bridge would go
    into backup.
    
    If you lower the FDDI port cost from 4 to 3 on the bridge that has the
    2 ethernet ports in backup, it would cause that bridge to be closer to
    the root and hence would make both ports on that bridge go into
    forwarding while the 2 ethernet ports on the bridge that were in
    forwarding would go into backup. There is no way that I can think of
    having one port on one bridge and the other port on the second bridge
    be in forwarding in the configuration you have described.
    
    What is it that you are trying to achieve by having only one port of
    each DB900MX be in forwarding ? One way to make this happen is to
    disable port 3 on the bridge that is going into forwarding. That would
    cause the port 2 of the other bridge to enter the forwarding state. But
    in this case you lose the advantage of redundancy, in case the bridge
    that is in forwarding resets, then the other bridge would not enter
    forwarding until you manually enable the disabled port.
    
    Hope this helps and that I haven't confused you more.
    Krishna
1915.2Aha...ANTIK::JONSSONLars JonssonWed Jan 25 1995 11:5414
Krishna,

Thanks for your very fine explanation.

I asked because I was confronted with a configuration where two bridges were
placed in separate hubs. Port 1 on a bridge should connect an DECrepeater900TM
in the hub. Port 2 should connect a DECrepeater900TM in the other hub via a
twisted pair cable. Now, I thought it would be easier for the customer to
understand the configuration, if the port connected internal in the hub were in
a forwarding state, and the "redundant via UTP port" were in backup.

Thanks again,

Lars