metrics = hops?

Discussion in 'MCSE' started by Gordon J. Rattray, May 28, 2004.

  1. Hi there,

    Studying a bit about metrics in RRAS and that and trying to get a grasp on
    metrics.

    Is a metric equal to a hop or what?

    Gordon
     
    Gordon J. Rattray, May 28, 2004
    #1
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  2. Yes, traditionally. Now, however, a metric represents what is
    essentially the "cost" of the path.

    Laura
     
    Laura A. Robinson, May 28, 2004
    #2
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  3. To an extent. Really, the metric specifies the cost of following a
    particular route. A number of factors can affect the metric, including hop
    count, speed/reliability/throughput of the path, or a conscious choice by
    the administrator to select a specific path.
     
    Patrick Kremer, May 28, 2004
    #3
  4. All routing protocols have to rank possible paths
    between routers. The term "metric" is just a
    generic term for whatever measurements are used
    to achieve this ranking.
    The simplest routing protocol is RIP.
    It's only metric is the hop count.
    The hop count is merely the number of routers
    along the proposed path.
    This is easy to conceptualize and implement, so
    it's a great learning tool to start with RIP.
    However, this is also a pretty bad
    metric in the real world; because, it is
    unlikely to be the best path except in small, very uniform
    networks. Just like with driving directions, you don't
    care much about how many roads are involved,
    you mostly just want to know how to get to the fastest freeway.
    Other routing protocols may offer a long list of metrics.

    "Cost" is a popular metric. It is usually assigned
    manually, or it can be an inverse function of the bandwidth.
    Other metrics that some routing
    protocols may use are reliability (how often the route is 'up'),
    delay (latency across a device), even corporate
    relationships can be factored in.
    When I studied for the MCSE, I only recall learning
    about RIP and OSPF for RRAS.

    btw, this stuff is cool to learn and all, but no one turns their PC's
    into routers by sticking multiple nic cards in them and running RRAS.
    A network of even middling size or complexity will use actual routers.
    PC's are fun for users, but don't make great infrastructure devices.

    Hope this helps.

    =====================
     
    J. Q. Etuo, MSCE/CCNA/A+, May 28, 2004
    #4
  5. Gordon J. Rattray

    Gavin Miller Guest

    Note "Cost" determines the best route therefore the lower the cost the
    better the route.
     
    Gavin Miller, May 31, 2004
    #5
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