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Conference 7.286::fddi

Title:	FDDI - The Next Generation

Moderator:	NETCAD::STEFANI

Created:	Thu Apr 27 1989
Last Modified:	Thu Jun 05 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	2259
Total number of notes:	8590

1476.0. "One Span.Tree many subnets" by ANGLIN::BERNDT () Mon Oct 17 1994 15:54

    
    I am a Warrior SE covering the Central Region. I have an opportunity
    with a pretty good size client.
    
    I would like your opinion on how the Gigaswitch will fit into their
    network.
    
    I have summarized below, a description of their existing network, and
    their future needs.
    
    Could you please respond to this note or directely to me...a phone
    call will be fine...I am at 414-852-2687. Thanks in advance. 
    
                              Client Network Today
    
    The key components in the network backbone today are three (3) Cisco
    AGS+ routers connected in an FDDI ring.
    
    Their traffic is composed of: 
    
    35% TCP/IP (800 hosts today moving to ~2000 in the future as they move
    more PC's and Workstations to TCP/IP.
    
    60% is a combination of DECnet, bridging (LAT/LAVC) and a little
    Banyan Vines. The DECnet is comprised of three areas, having in total
    1800 DECnet nodes.
    
    They are running Pathworks 5.0 and 5.1.
    
    Note: Worldwide the parent company has 20,000 to 30,000 nodes, 15
    Class B addresses and several Class C addresses.  The client our
    visited in particular has one Class B address in use now, and just got
    another to use for Variable length masking (a feature Cisco has
    released as an upgrade to their router code).
    
                                 The Question?
    
    Considering that a Gigaswitch is a bridge, and that it employs one
    spanning tree per box, how can it effectively be used in a network
    such as this? One objective may be to switch on the backbone versus
    routing from AGS+ to AGS+ to AGS+ which has inherent latency.
    
    A consultant recently stated some things about "virtual LANs" that may
    apply to GIGAswitch/FDDI --A virtual LAN is analogous to a
    transmission control protocol/internet protocol (TCP/IP) subnet,
    DECnet area or AppleTalk zone - the only difference is that the subnet
    no longer has set physical boundaries.  It becomes a logical subnet,
    or logical grouping of devices not dependent on location.  This is no
    simple task to either define or implement.  There are no standards for
    virtual LAN, therefore, each vendor is solving the virtual LAN issue
    in a unique and proprietary fashion.  There are three broad approaches
    to virtual LANs.
    
                   One Big Virtual LAN: (GIGAswitch"like")  
    
    
    
    
    
    
    The simplest approach, but the least likely one to be implemented, is
    the installation of one big virtual LAN.  This would technically be
    the same as a single subnet, or a large bridged network. In the past,
    the problems with large bridged networks were overcome by routers and
    protocol segmentation.  With a single virtual LAN, these problems
    would all return, including the need to readdress any subnets into a
    single subnet.  Many protocols will not operate as a flat address
    space in large networks, and many companies do not have internet
    protocol (IP) addresses that can scale to encompass their entire
    network.  The value in virtual LANs comes with having more than one
    and being able to communicate among them effectively, translating
    existing subnets into logical subnets.  Unless the network is small,
    we do not believe that this is an option in a mixed-legacy LAN-ATM
    environment.
    
    cross posted to SCHOOL::GIGASWITCH

T.R Title User Personal
Name Date Lines

1476.1 Don't consider it unless you want to make network management easier 40222::PETTENGILL mulp Sat Oct 29 1994 00:29 16

T.R	Title	User	Personal Name	Date	Lines
1476.1	Don't consider it unless you want to make network management easier	40222::PETTENGILL	mulp	`Sat Oct 29 1994 00:29`	16
	Using routers is job security. When one segment is overloaded, you get to move systems to new segments and change all the addresses. That requires a good bit of discipline and care, and because of the disruption, will justify paying a lot of money to someone who does it well. If you just connected everything to the switch, it would be trivial to balance the load between segments; just move the connection to another segment, and after a few moments of learning the bridges will learn the new location. Of course, you might argue that this will greatly improve performance, but it will require extreme skill to prevent broadcast storms from taking down the network. Then you retire to your office for a nap because the rate limiting in the switch will prevent that from being a problem that you must react to. :-)

Using routers is job security.  When one segment is overloaded, you get
to move systems to new segments and change all the addresses.  That requires
a good bit of discipline and care, and because of the disruption, will
justify paying a lot of money to someone who does it well.

If you just connected everything to the switch, it would be trivial to balance
the load between segments; just move the connection to another segment, and
after a few moments of learning the bridges will learn the new location.

Of course, you might argue that this will greatly improve performance, but
it will require extreme skill to prevent broadcast storms from taking down
the network.  Then you retire to your office for a nap because the rate
limiting in the switch will prevent that from being a problem that you must
react to.

		:-)