Chuck,
Proxy-arp is also useful for cases where you have multiple
candidate DG's on the same segment and for whatever reason you
can't or don't want to use HSRP/VRRP, IRDP or passive RIP.
You can achieve a certain amount of load-balancing and failover
using proxy-arp by pointing a hosts DG to its own address and
setting the timeout for arp entries very low on the end-stations.
Course, this increases the amount of ARP bcasts on the segment
and is, essentially, a "cool hack", but it does work.
Regards,
Kent
On 23 May 2001, at 22:36, Chuck Larrieu wrote:
> At the risk of becoming another Bob Vance......
>
> I'm reading Doug Comer's TCP/IP reference, on the assumption that it
> can't hurt to really get into how TCP/IP works.
>
> Proxy-arp versus normal arp.
>
> A host does not know the physical address of another host so it sends
> out an ARP request. If the host in question lies on another network, a
> router responds to that request. Proxy ARP, correct?
>
> A host through it's TCP stack does the XOR and determines that a host
> lies on another network. The host therefore sends the packet to the
> device indicated as its default gateway in its configuration. It sends
> an ARP request for the MAC of the default gateway. Normal ARP?
>
> So in other words, proxy arp may be viewed as something of an obsolete
> protocol / operation in that most modern TCP stacks contain the
> mechanisms for doing the network XOR determination, and then using the
> default gateway. A modern stack would recognize that a host is on a
> different network and go the default gateway route, so to speak.
>
> In other words, the necessity for proxy arp is eliminated for the most
> part because of the default gateway concept and the modern TCP stack.
>
> Has it sunk through this thick head finally?
>
> PS Comer states that proxy arp is aka arp hack. :->
>
> Chuck
>
> One IOS to forward them all.
> One IOS to find them.
> One IOS to summarize them all
> And in the routing table bind them.
>
> -JRR Chambers-
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