On Fri, 18 May 2001, David Chandler wrote:
> Just completed a lab on Proxy-ARP behavior, and thought I'd share the
> results.
>
> Last week there was a thread about proxy-arp and someone pointed out the
> cisco documentation which states "the Cisco IOS software evaluates
> whether it has the BEST route to that host. If it does, the device sends
> an ARP Reply". I was not positive about what was meant by "BEST route"
> so I tested it out.
Just out of curiosity, have you tried what happens when the interface
the ARP request comes in has multiple addresses, and both the source and
the destination of the ping are on it, but on different prefixes? I
would publicly predict what I think will happen, but I don't want to
bias your experiments. :-) *cough*
> ###########
>
> Setup:
> #1. I setup a misconfigured host to generate the arps. 4.1.1.101/8 will
> ping 4.1.2.1
> #2. R1, R2, & R3 with subnets that included the host's address but with
> 4.1.1.x/24 addresses.
> #3. Sniffer to verify who is doing what.
>
> Assumptions:
> IP PROXY-ARP enabled.
> Router has a route for the arp'd subnet (not directly connected)
>
> ###########
>
> Results:
> A proxy-arp is sent IF the following three conditions are met.
>
> #1. Arp received on an interface whose IP/Mask (subnet range) does not
> belong the the requested IP address of the arp.
>
> #2. The router has a route in the table to the requested subnet. (If #1
> is true then it will NOT be directly connected.)
>
> #3. The routing table's next hop is NOT reached via the interface the
> arp came in on.
>
> ############
>
> Side notes:
> Tried the setup with rip, eigrp, & ospf with various metrics AND static
> routes interface and next-hop.
> The routing protocol made no difference.
> The host (NT workstation) used the MAC of whoever responded first.
> Running HSRP made no difference other than the MAC address.
>
> #############
>
> Please reply if there are other quirks,
> There is always some small detail/senerio that changes the behavior of
> these protocols.
>
>
>
> DaveC
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>
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