From: Pickell, Aaryn (Aaryn.Pickell@xxxxxxxxxxxxx)
Date: Mon Apr 02 2001 - 20:23:05 GMT-3
Proxy arp is also useful when you have your subnet masks misconfigured.
Say, for example, the router has two /24 segments attached. If there is a
host configured with a /23 instead, it will try arping for addresses which
are not actually directly connected. The router will respond with its own
MAC and then forward the traffic.
They use this in access servers as well. Assume a large modem bank on an
AS5300, with a bunch of users dialing in. Each of these users is given an
address from the segment that's attached to the ethernet segment. When
hosts actually on that ethernet wish to talk to the dial-in users, they
believe them to be directly connected, so they arp. The AS5300 will respond
with its own MAC and forward the packets correctly.
Aaryn Pickell - CCNP, CCDP, MCSE
Senior Engineer - Routing Protocols
Getronics Inc.
Direct: 713-394-1609
Email:aaryn.pickell@getronics.com
> -----Original Message-----
> From: Bowen, Shawn [mailto:sbowen@neteffectcorp.com]
> Sent: Monday, April 02, 2001 5:50 PM
> To: Tariq Sharif; Ccielab@Groupstudy. Com
> Subject: RE: Proxy ARP
>
>
> With Microsoft clients there is a way to "Set all segments as
> local" so to
> speak, I forget how off the top of my head but this will work
> as well. Now
> as to proxy ARP, the workstation, be it Unix or Microsoft looks at the
> destination IP and compares it's own IP and MASK to see if it
> is local, if
> it is then it will be encapsulated in an Ethernet (or whatever other
> topology you are using) frame and then put on the wire, if
> the destination
> network is on a different segment then your machine will not
> know what to do
> with it unless there is a default gateway setup (or you set
> "all subnets
> local"). This is why you are seeing this; it is perfectly
> normal in the
> Unix, Novell, and Windows world.
>
> As another example. With a Microsoft dial-up
> networking setup you
> set it to obtain it's address automatically, sometime do a
> "winipcfg" on
> 95/98 or an ipconfig /all in NT and check out your IP and
> Default gateway,
> they will normally be the same, this is because the ISP is
> doing proxy arp
> and the machine then knows to send ALL traffic to the
> interface as local
> traffic, the router will deal with the rest.
>
> Shawn
>
> -----Original Message-----
> From: Tariq Sharif [mailto:tariq_sharif@btinternet.com]
> Sent: Monday, April 02, 2001 6:31 PM
> To: Ccielab@Groupstudy. Com
> Subject: Proxy ARP
>
> In Doyle's TCP/IP book (page 69-70) & in other text there is
> about Proxy
> ARP. Says that hosts without any default gateway can be issue
> ARP & LAN
> router (knowing where the destination is) will issue PROXY
> ARP reply. So the
> local host (without default gateway) can reach remote hosts.
> I can't see
> this working with NT 4 or Win 95 unless I assign the PCs own
> address as its
> default gateway. My question is, do Unix clients behave the same as
> Microsoft clients? If so, what am I missing?
>
>
> Many thanks & regards.
>
> Tariq Sharif
>
> [demime 0.98b removed an attachment of type
> application/ms-tnef which had a
> name of winmail.dat]
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