Do I need proxy ARP if default gateway is set ?

[mohammed hashim]

hi,

I see proxy ARP is not well documented, but after reading couple of documnets, I concludes that proxy ARP is not needed if the default gateway is set on endpoints machines, 

HostA--------------R1--------------HostB

if HostA wants to communicate with HostB, then since this subnet out of its network, it will forward the traffic to the gateway, which means proxy ARP is not triggered,

Am I right ?

[Richard Burts · Accepted solution]

Yes you are correct that in the case that you describe proxy arp is not triggered. So you do not need proxy arp.

HTH

Rick

[mohammed hashim]

Thanks Richard,

[Richard Burts]

You are welcome.

HTH

Rick

[Joseph W. Doherty]

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Posting

As a side note, if you had R1 and R2 on network with hostA, and hostB was best reached via R2, but R1 was configured as hostA's default gateway, R1 would forward the packet to R2 and, assuming R1 wasn't configured to not do so, R1 would send a redirect to hostA informing it to use R2 to get to hostB.

[mohammed hashim]

Hi Joseph,

but how is that related to Proxy ARP  ?

                                R1----------R3

                                 |                |

HostB-------SW-------             HostB

                                 |                |

                                R2----------R4

if R1 send ICMP redirect message to HostA telling it use R2, then HostA will ARP for R2 IP address (not Proxy ARP) !!

[Joseph W. Doherty]

but how is that related to Proxy ARP ?

It's not but your original question was also asking about default gateway over riding the need for proxy ARP (which was answered by Rick).

Mine was just an additional note that when you use a host's default gateway, depending on the situation, your host might "automatically" stop using default gateway for a destination.

[mohammed hashim]

Thanks for your note Joseph, it is clear :)