ARP discovers MAC on the same subnet? - Networking

This is a discussion on ARP discovers MAC on the same subnet? - Networking ; Hi All I am finding that ARP assigns the gateway MAC for addresses outside the subnet. For instance: Ping from 172.16.170.30 to 172.16.170.35 adds an entry for .30 in ARP table of .35. Vice versa. Ping from 172.16.170.30 to 10.170.100.21 ...

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Thread: ARP discovers MAC on the same subnet?

  1. ARP discovers MAC on the same subnet?

    Hi All

    I am finding that ARP assigns the gateway MAC for addresses outside
    the subnet. For instance:

    Ping from 172.16.170.30 to 172.16.170.35 adds an entry for .30 in ARP
    table of .35. Vice versa.

    Ping from 172.16.170.30 to 10.170.100.21 adds an entry for .21 in ARP
    table with the MAC address of the gateway. Vice-versa.

    Is this what one can expect from ARP?

    Thought, ARP will cache all of the MAC addresses on the intranet.

    Thanks.

  2. Re: ARP discovers MAC on the same subnet?

    soup_or_power@yahoo.com wrote:
    > Hi All
    >
    > I am finding that ARP assigns the gateway MAC for addresses outside
    > the subnet. For instance:
    >
    > Ping from 172.16.170.30 to 172.16.170.35 adds an entry for .30 in ARP
    > table of .35. Vice versa.
    >
    > Ping from 172.16.170.30 to 10.170.100.21 adds an entry for .21 in ARP
    > table with the MAC address of the gateway. Vice-versa.
    >
    > Is this what one can expect from ARP?
    >
    > Thought, ARP will cache all of the MAC addresses on the intranet.


    ARP is a layer 2 protocol. It only discovers MACs on the same network
    segment.

    If you don't have your subnet sizes set correctly, but you have your
    gateway "proxy" arps for things beyond it, then the gateway will respond
    with its MAC for things beyond it. In other words, there are some
    scenarios where a smart gateway can keep a poorly-configured network
    device from being orphaned. That's what you're seeing.

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