Subject: Amended DS/Topology Exchange

From: [email-masked] (PNGacek)
Date: Mon, 26 Jul 93 07:32:39 MDT

Hello All

I am resending this with a corrected typo in the description of d), CU20 
should 
read CU30.

Regards Paul Gacek

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Directory Servers and Topology Exchange

I believe we are discussing a number of different items and want to 
make sure we clarify what they are. 

The discussion is about WHAT is exchanged with WHOM. 

WHATs could be end station MAC/IP address pairs or could be DLSw box 
IP addresses. 

WHOMs could be a Directory Server/DLSw box pair or could be a pair of 
DLSw box.

Consider the diagram below. Four DLSw boxes exist labelled DLSw1 through
DLSw4. DLSw1 through DLSw3 have a single token ring attached Controller,
CUx0. DLSw1 is connected (via a TCP connection (pair?)) to DLSw4 and 
DLSw2,
while DLSw4 is connected to DLSw2. Initially DLSw3 is NOT connected to 
any
other DLSw box. The remainder discusses how DLSw3 gets info about the 
DLSw network it is joining.

                      +------+   +-----+
                      | DLSw1|-o-| CU10|
                      +------+   +-----+  
                          . .   
                         .   .           
                        .     . 
                       .       .
+----+   +------+......         ............+------+   +-----+          
|Host|-o-| DLSw4|...........................| DLSw2|-o-| CU20|            

+----+   +------+                           +------+   +-----+            

                      +------+   +-----+
                      | DLSw3|-o-| CU30|
                      +------+   +-----+  
                                                                        
1. POSSIBLE WHATs CANDIDATES

	1. List of DLSw box IP addresses
	2. List of end station MAC addresses LOCAL to a single DLSw box
	3. List of ALL end station MAC addresses and associated IP address
		(this is just multiples of 2 above)

1.1 LIST of DLSw BOX IP ADDRESSES

This list consists of the IP addresses of all known DLSw boxes. This 
list does NOT consist of end station MAC addresses. In the diagram 
above the list consists of the IP address of DLSw1, DLSw2, DLSw3 and 
DLSw4.

1.2 LIST of LOCAL MAC ADDRESSES

This list consists of MAC addresses of devices locally attached to a 
DLSw box. In the diagram above a list exists for each DLSw box as 
follows: 
	DLSw1 knows about MAC addr CU10
	DLSw2 knows about MAC addr CU20 
	and so on

1.3 LIST of ALL KNOWN MAC ADDRESSES

This is a list of all the local lists defined in 1.2 above.
  
2. POSSIBLE WHOM CANDIDATES

2.1 DIRECTORY SERVER

A directory server is some specially designated box (possibly a DLSw 
box or management station) that holds DLSw pertinent information. 

2.2 DLSw BOX 

You can guess  this one.

So back to the original statement about WHAT is exchanged by WHOM.

The table below has the WHATs as rows and pairs of WHOMs as the columns.

                        |  DS/DLSw    |    DLSw/DLSw  |
------------------------------------------------------|
                        |             |               |
DLSw IP Addresses       |     a       |        b      |
                        |             |               |
------------------------------------------------------|
                        |             |               |
DLSw Local MAC Addr     |     c       |        d      |
                        |             |               |
------------------------------------------------------|
                        |             |               |
All MAC Addr            |     e       |        f      |
                        |             |               |
------------------------------------------------------|

For discussion purposes consider DLSw4 is a Directory Server (DS). 

a) DS/DLSw & DLSw IP List 

With this one, each DLSw box gets a list of IP addr of other DLSw 
boxes from a DS. So in the above example, DLSw4 (the DS) knows the 
IP addresses of DLSw1, DLSw2 and DLSw3 (via configuration or some 
other means). DLSw3 knows the address of the DS (i.e DLSw4's IP 
address) and establishes contact with it and recovers the IP address 
list. In this example DLSw3 gets the list and establishes TCP 
connections to DLSw1, DLSw2 and DLSw4.

Advantages:
1. Configure the DLSw domain members IP addresses at 1 single place. 

Disadvantages:
1. Need a backup DS mechanism in the event the primary DS is down.

b) DLSw/DLSw and DLSw IP List

Don't think this one makes sense.

c) DS/DLSw and DLSw Local MAC Addrs

With this one a DLSw box recovers info about the end station MAC addr 
that are locally attached to itself.

Don't think this one makes sense. 

d) DLSw/DLSw and DLSw Local MAC Addrs

With this one two DLSw boxes exchange lists of the locally attached 
MAC addresses. So in the example above, DLSw3 establishes a TCP 
connection with DLSw1. DLSw1 sends a list containing 1 entry - the MAC 
addr of CU10 and DLSw3 sends a list containing the MAC addr CU30. 

Advantages
1. Only exchange information about end stations attached to a DLSw box.

e) DS/DLSw and All MAC Addrs

With this one a DS contains info about all known MAC addr in a DLSw 
network. So in this example DLSw3 establishes a connection with DLSw4 
and gets the following info:
	DLSw4 - Host MAC Addr
	DLSw1 - CU10 MAC Addr
	DLSw2 - CU20 MAC addr

Advantages
1. Info defined in 1 place
2. Directed CUR are initially used in place of broadcast CUR (due to 
high cache hit rate). 

Disadvantages
1. Need backup DS mechanism
2. Information gets out of date easily

f) DLSw/DLSw and All MAC Addrs

With this one, every time a DLSw-DLSw TCP connection is established a 
list of all known MAC addr are exchanged. So in the above example, 
when DLSw3 connects with DLSw4 it gets the following:
	DLSw4 - Host MAC Addr
	DLSw1 - CU10 MAC Addr
	DLSw2 - CU20 MAC addr
and then when DLSw3 connects to DLSw1 it gets the exact same info and 
so on for each DLSw-DLSw connection.

Advantages
1. No dependency on a DS.

Disadvantages
1. Potentially sending the same info multiple times to a newly entering 
DLSw box.
 
I personally favour using both a) and d).

Regards Paul Gacek
Novell