Carrier Ethernet

Discussion in 'Cisco' started by Mark, Oct 6, 2012.

  1. Mark

    Mark Guest

    Mark, Oct 6, 2012
    #1
    1. Advertising

  2. In article <>,
    Robert Wessel <> wrote:

    > On Fri, 5 Oct 2012 23:57:04 -0400, "Mark"
    > <> wrote:
    >
    > >Hello,
    > >
    > >they often say, for example http://en.wikipedia.org/wiki/Carrier_Ethernet
    > >that such concepts as "bridge" or "spanning tree" don't scale well to large
    > >networks. What exactly is meant here by "scale" ?

    >
    >
    > Quite simply that bridges and the spanning tree protocol won't work on
    > really large networks. For example, most bridges (switches) can only
    > learn a few tens of thousands of MAC addresses - and if there are more
    > devices than the bridges can learn, frames get broadcast to all
    > attached LANs. Further the way that addresses are propagated around
    > the network, and how the network organizes itself, also fairs poorly
    > in large networks.


    Anyone remember back in the 80's when the telecoms thought that they
    could build nationwide networks as a single (or maybe a few large) ATM
    cloud?

    --
    Barry Margolin,
    Arlington, MA
    *** PLEASE post questions in newsgroups, not directly to me ***
    Barry Margolin, Oct 6, 2012
    #2
    1. Advertising

  3. Mark

    Michelot Guest

    Hi, Mark

    > they often say, for examplehttp://en.wikipedia.org/wiki/Carrier_Ethernet
    > that such concepts as "bridge" or "spanning tree" don't scale well to large
    > networks. What exactly is meant here by "scale" ?


    Bridges are indeed used in network providers.

    Spanning tree is generally not used. If the provider is adding a
    bridge, STP would disrupt its network too long time, to converge.

    In Ethernet WAN, we consider connectionless paths (CL) and oriented
    connection paths (CO). With CO paths, address learning process is
    useless.

    Best regards,
    Michelot
    Michelot, Oct 6, 2012
    #3
  4. Mark

    Stephen Guest

    On Fri, 05 Oct 2012 23:43:54 -0500, Robert Wessel
    <> wrote:

    >On Fri, 5 Oct 2012 23:57:04 -0400, "Mark"
    ><> wrote:
    >
    >>Hello,
    >>
    >>they often say, for example http://en.wikipedia.org/wiki/Carrier_Ethernet
    >>that such concepts as "bridge" or "spanning tree" don't scale well to large
    >>networks. What exactly is meant here by "scale" ?

    >
    >
    >Quite simply that bridges and the spanning tree protocol won't work on
    >really large networks. For example, most bridges (switches) can only
    >learn a few tens of thousands of MAC addresses - and if there are more
    >devices than the bridges can learn, frames get broadcast to all
    >attached LANs. Further the way that addresses are propagated around
    >the network, and how the network organizes itself, also fairs poorly
    >in large networks.


    Bridging has some tables and overheads that grow faster than linear
    with the number of connections and devices across the entire set of
    indirectly connected switches.

    Every end point connected to a bridged system has at least 1 MAC
    address, and any traffic to that device implies that MAC has entries
    in some or all the devices that make up the network.

    This means linear scaled up table space is needed, but the maintenance
    overheads that occur grow more quickly as well.

    The other practical problem is that a network needs to be stable to
    operate well, and in practice that means that you need ways to limit
    changes to parts of the system so their effect stay local.

    in bridging a topology change can propagate across the system.
    >
    >Routing, OTOH, is much more hierarchical, and network interconnections
    >are managed much more explicitly, so it scales far better. Basically
    >the Internet is all routed (as opposed to bridged), with the obvious
    >exception of relatively local and small bridged networks (usually
    >smaller than a few thousand nodes).


    Think of the hierarchy in routing as being selective information
    hiding.

    Instead of 1 entry per MAC address for 100,000 devices in table for a
    big corporate network, you may need just 1 or a few routing entries
    saying "xxx corp is that way".

    This means any topology change in xxx corp stays within their system -
    the rest of the system doesnt need to see it
    --
    Regards

    - replace xyz with ntl
    Stephen, Oct 6, 2012
    #4
  5. Mark

    Michelot Guest

    Hi Stephen,

    > Every end point connected to a bridged system has at least 1 MAC
    > address, and any traffic to that device implies that MAC has entries
    > in some or all the devices that make up the network.


    In the user plane, a bridge is not a MAC end point.

    Best regards,
    Michelot
    Michelot, Oct 7, 2012
    #5
  6. Mark

    Rick Jones Guest

    In comp.dcom.lans.ethernet Robert Wessel <> wrote:
    > Quite simply that bridges and the spanning tree protocol won't work
    > on really large networks. For example, most bridges (switches) can
    > only learn a few tens of thousands of MAC addresses - and if there
    > are more devices than the bridges can learn, frames get broadcast to
    > all attached LANs.


    Wording quibble. Given the loaded nature of the word "broadcast" it
    might be better to put that as "frames get transmitted out all
    connected ports" or "frames get flooded out all connected ports" lest
    some new folks think the frames get transformed into actaul broadcast
    frames.

    rick jones
    --
    web2.0 n, the dot.com reunion tour...
    these opinions are mine, all mine; HP might not want them anyway... :)
    feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...
    Rick Jones, Oct 8, 2012
    #6
  7. In comp.dcom.lans.ethernet Mark <> wrote:

    > they often say, for example http://en.wikipedia.org/wiki/Carrier_Ethernet
    > that such concepts as "bridge" or "spanning tree" don't scale well to large
    > networks. What exactly is meant here by "scale" ?


    The meaning of "scale" is in the sense of how one quantity must
    change when you change another.

    One can, for example, discuss the change in the size of the legs
    of an animal with its weight. That is:

    "How does an animal's leg scale with its weight?"

    In many interesting and useful cases, the answer is an exponent.

    How does a tree trunk diameter scale with tree height?

    How does the speed of a transistor scale with its size?

    How does the cost of a transistor scale with it speed or size?

    Doesn't scale means that something else happens, such that
    the scaling laws aren't useful anymore.

    Transistors (and animals) don't scale well down to atomic size.
    They also don't scale well up to planetary size.

    -- glen
    glen herrmannsfeldt, Nov 1, 2012
    #7
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. Peter
    Replies:
    2
    Views:
    1,020
  2. darren butts

    VPN Debug - Lost Carrier

    darren butts, Jul 19, 2004, in forum: Cisco
    Replies:
    0
    Views:
    589
    darren butts
    Jul 19, 2004
  3. Miles
    Replies:
    3
    Views:
    12,589
  4. No_Problem
    Replies:
    0
    Views:
    585
    No_Problem
    Feb 13, 2007
  5. RMW
    Replies:
    4
    Views:
    745
    Thrill5
    Sep 18, 2009
Loading...

Share This Page