Re: ARP request retransmitting

From: John-Mark Gurney (gurney_j_at_resnet.uoregon.edu)
Date: 11/08/05

  • Next message: Charles Swiger: "Re: ARP request retransmitting" 
    Date: Mon, 7 Nov 2005 15:45:48 -0800
To: Charles Swiger <cswiger@mac.com>

    Charles Swiger wrote this message on Mon, Nov 07, 2005 at 18:17 -0500:
    > On Nov 7, 2005, at 5:43 PM, John-Mark Gurney wrote:
    > >>While that "other hand" is true, here at RPI we deal with some of
    > >>those other-hand issues by simply turning them off. We turn off
    > >>multi-cast by default on some of our networks, for instance. But
    > >>there's no way we can turn off ARP, so I think more care needs to
    > >>be taken to make sure ARP remains network-friendly.
    > >
    > >And most places that have VERY large number of hosts in a broadcast
    > >domain (a partially populated class b), have smart switches that cache
    > >arp requests, and prevent the arp traffic from killing the network...
    >
    > Really? You're saying that "tcpdump -nt arp" never shows any
    > requests except those made by the local host?
    >
    > Which vendor and which switch model?

    Just a random search for smart arp large, turned up user's manual
    for the WaveSwitch 9000, from Plaintree Systems..

    The docs say:
    Address Resolution Protocol (ARP) is the means by which a host or router
    maps an IP address to a physical address. WaveSwitch 9000 software
    contains the SmartARP feature that allows for reduced impact of ARP
    broadcasting.

    Normally, ARP broadcasts are flooded to all ports on a switch. Switch
    ports that are not connected to the target host must, therefore, receive
    and partially process the broadcast frames. This can potentially affect
    the performance of all hosts on the bridged network.

    With the SmartARP feature, ARP broadcasts are confined to only the
    applicable switch ports (see Figure 67).

    And the diagram shows the arp request being restricted to only the
    port with the router and the host on it...

    A coworker also says that the Foundary switches can do it, and did
    it like five years ago... I haven't confirmed this myself...

    > Smart switches will generally keep track of 1000 or 4000 or so MAC
    > addresses and the ports those MACs are associated with, but I am not
    > aware of anything in them which blocks ARP traffic or anything else
    > which uses the all-ones broadcast MAC address. I can see ARP
    > requests going out from any/all of the other machines on the network
    > I'm using right now (using several 3com SuperStack 3300's), and I've
    > seen the same thing on networks using the HP Procurve or Cisco 29xx
    > switches.

    I'd imagine you have to turn it on... since it'd have odd behavior if
    you weren't expecting it... 

    -- 
  John-Mark Gurney				Voice: +1 415 225 5579
     "All that I will do, has been done, All that I have, has not."
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  • Next message: Charles Swiger: "Re: ARP request retransmitting"

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