[26867] in resnet
Re: Windows 7/2008 not connecting to network...
daemon@ATHENA.MIT.EDU (James J J Hooper)
Sat Oct 15 06:44:08 2011
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Message-ID: <4E996386.4030609@bristol.ac.uk>
Date: Sat, 15 Oct 2011 11:42:14 +0100
Reply-To: Resnet Forum <RESNET-L@listserv.nd.edu>
From: James J J Hooper <jjj.hooper@bristol.ac.uk>
To: RESNET-L@listserv.nd.edu
In-Reply-To: <CANtPpk5psMzJKJtbB1TucDiRMVAPh8CiTpwi82YXzJdUwMypWw@mail.gmail.com>
On 12/10/2011 22:56, Mike King wrote:
> I've also had "Issues" with Cisco ASA's and Server 2008 being in the same
> subnet.
>
> Short answer,
> Cisco ASA's have a "feature" called proxy arp, where if a device is
> misconfigured with the wrong gateway, the ASA will still respond, and
> mimic the wrong address, so your clients can connect to the network.
>
> Server 2008/Windows 7 use proxy arp to detect ip address conflicts. This
> causes them to completely freak out.
>
> On a sad note, when you have an address conflict, it does not show a popup
> like XP used to. It will just show a different (usually APIPA address) as
> "Preferred" in the ipconfig /all
Although 2008/Win7 may behave differently to previous Windows versions[?],
a host ARPing for an IP it is considering using (e.g. when getting a lease
by DHCP) is a standard practice. Refer to section 2.2 for RFC 2131 (DHCP RFC).
Proxy ARP should be used when your ASA is acting as a bridge (purely layer
2). It's not required if your ASA is acting as a router, and should be
disabled (it's not there to catch mis-configured devices :) ).
-James
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