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  • Routers...

    Aight, i have two questions:

    1. How long does a packet stay in a store and forward router before it is deleted?


    2. Is there anyway to avoid a hop when sending packets from source to destination. Can i tell it not to go through a hop, or does it all depend on the network my connection medium travels through?
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  • #2
    Re: Routers...

    Originally posted by Syntax Driven
    Aight, i have two questions:

    1. How long does a packet stay in a store and forward router before it is deleted?
    Depends on how the router is configured.

    2. Is there anyway to avoid a hop when sending packets from source to destination. Can i tell it not to go through a hop, or does it all depend on the network my connection medium travels through?
    You can build route maps to send certain types of traffic on pre-defined routes, but otherwise, no.

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    • #3
      cisco'ly speaking the store and forward is more of a switching term than a router term. in switching you have cut through, fragment free (modified cut through) and store and forward. store and forward is the default config on the cisco switches. (i'm sure it applies to other vendors as well)

      when the router gets the frame (of the ethernet wire) it will discard it and be left with the tcp/ip packet and depending on the flags are set within that and as stated above how the router is configured to deal with the flags, will depend on the latency.

      and i have never seen route maps, but it sounds pretty cool. i mean, how would you even begin to set something like that up knowing that the backbone is running bgp, has qos and multiple routes? could some shmoe just craft packets and set flags and see what happens?

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      • #4
        Re: Routers...

        Originally posted by Syntax Driven
        Aight, i have two questions:

        1. How long does a packet stay in a store and forward router before it is deleted?
        Not exactly sure what you mean here. Do you mean how long can an IP packet be held in buffer before the router just drops is rather than forwarding it?

        If so, it's really a difficult question to answer--sort of like "how long does it take a car to go from 0-60". It depends on the buffering capabilities of the router, the kind of router (how much horsepower), and the utilization on the outbound link(s).

        I've personally seen packets buffered for well over a second, but it was a beefy router, and the buffers were huge.


        2. Is there anyway to avoid a hop when sending packets from source to destination. Can i tell it not to go through a hop, or does it all depend on the network my connection medium travels through? [/B]
        No, a sender can't tell it to take a certain route through a network (at least not that I'm aware of). A network admin can do whatever he wants to the routing tables using things like static routes, policy-based routing, and route-maps, but generally the path is left up to routing algorithms like OSPF, EIGRP and BGP.

        Sounds like you have a specific hop that you're trying to avoid due to ongoing congestion. If that's the case, your only option is to get another ISP.

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