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From: Leonard@arizona.edu (Aaron Leonard)
Newsgroups: comp.dcom.sys.cisco
Subject: poor inter-area routed DECnet performance (long)
Keywords: DECnet area
Message-ID: <21919@megaron.cs.arizona.edu>
Date: 7 Jun 90 20:14:59 GMT
Sender: news@cs.arizona.edu
Reply-To: Leonard@Arizona.EDU
Organization: Univ of Ariz Telecom
Lines: 64

We have experienced what you might call negative synergy
between DECnet traffic being routed thru a cisco and
then between level II routers. 

The case in which the difficulty emerges is somewhat 
complicated to explain, but quite reproducible, so please bear
with me.

                     [ UAZHE0   46.437 ]   [ UAZHE4  46.365 ]
                     [ level II router ]   [    endnode     ]
                          |                  |
[ MAGGIE   50.204 ]--(  large bushy bridged   )--[ CIRRUS  50.140 ]
[ level II router ]  ( ethernet <128.196.128> )  [    endnode     ]
                          |
                     [ PANCHO   50.222 ]
( repeatered enet )--[  cisco AGS II   ]--( large repeatered       )
( <128.196.28>    )  [  level I router ]  ( ethernet <128.196.120> )
        |                                          |
  [ ECEVAX  50.111 ]                        [ DOC   50.231 ]
  [   endnode      ]                        [   endnode    ]

In the above picture, consider any endnode to be representative of a
large number of topologically identical endnodes.  We use the IP
subnet terminology simply as means of identifying Ethernets.  (All
connections above are ethernet; all DECnet nodes but PANCHO are
VAXen.

Note that this is an unusual configuration, in that we have nodes
in multiple DECnet areas residing on the same ethernet (on
128.196.128.)  (This is necessitated by the peculiarities of HEPnet
routing.)

We have found that traffic flows quickly (1) amongst all nodes in
this network EXCEPT for the case where DOC or ECEVAX (or any other
node in subnets 128.196.120 and 128.196.28) tries to communicate
with any node in area 46.  In that case, the traffic flow is
consistently an order of magnitude slower (2).  These results
have been verified by many tests using a large number of
pairs of nodes.

The traffic flow in the too-slow case is as follows: area 50 endnode
to PANCHO (AGS), PANCHO to MAGGIE (level II router for area 50), 
MAGGIE to UAZHE0 (lev II router for area 46), UAZHE0 to area 46
endnode.  Note that the lev II routers are NOT the bottleneck;
traffic that flows between e.g. CIRRUS and UAZHE4, which passes
thru MAGGIE and UAZHE0, but not thru PANCHO, is quick.  Note also
that PANCHO by itself is not the bottleneck, as traffic between
e.g. CIRRUS and DOC is quick.  The only case where traffic is slow
is where inter-area traffic is routed thru PANCHO.

Notes.

All traffic tests were run using DEC's DTSEND utility, via the following
command sequence:

$ MC DTSEND
Test: DATA/PRINT/STATISTICS/TYPE=ECHO/SIZE=500/SECONDS=60/NODE=node

This utility tests task-to-task NSP throughput between DECnet
phase IV nodes.

(1) "Quick" data flow is in the range of 400Kbps to 1.2Kbps.

(2) "Slow" data flow is in the range of 40Kbps to 100Kbps.