Why ARP response is not broadcast?

I guess this is a dumb question. Is it a big deal to broadcase the ARP
response to every host in the LAN? Thanks.

On Thu, 6 Nov 2008 17:51:45 -0800 (PST), Woden98
<wgao_personal@yahoo.com> wrote:

>I guess this is a dumb question. Is it a big deal to broadcase the ARP
>response to every host in the LAN? Thanks.

An ARP broadcast is a broadcast packet, which means it goes all over
the network. The ARP
who-has IP_address tell source_IP_address
packet asks everyone "who has this IP address". Only the holder of
the IP address responds with the packet going to the IP address
following the "tell". Therefore, the response only goes to the
originating IP address, not the entire network.

What problem are you trying to solve and what the hell is a "big deal"
in English or Metric terms?

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558 jeffl@comix.santa-cruz.ca.us
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS

I am just trying to understand the ARP protocol.

Broadcasting ARP request is easy to understand because the sender does
not know who has the MAC-IP mapping. Receiver broadcasting ARP
response is not a "big deal" which I mean that the ARP response does
not look flooding a lot of traffic to the network. If ARP response is
broadcasted, every host will have a chance to update their mapping
table so they don't have to send a ARP request any more later on when
they need it. But why in ARP protocol, the APR response is
specifically sent back to the the requester only? What is the
difference?



On Nov 6, 9:03*pm, Jeff Liebermann <je...@cruzio.com> wrote:
> On Thu, 6 Nov 2008 17:51:45 -0800 (PST), Woden98
>
> <wgao_perso...@yahoo.com> wrote:
> >I guess this is a dumb question. Is it a big deal to broadcase the ARP
> >response to every host in the LAN? Thanks.
>
> An ARP broadcast is a broadcast packet, which means it goes all over
> the network. *The ARP
> * who-has IP_address tell source_IP_address
> packet asks everyone "who has this IP address". *Only the holder of
> the IP address responds with the packet going to the IP address
> following the "tell". *Therefore, the response only goes to the
> originating IP address, not the entire network.
>
> What problem are you trying to solve and what the hell is a "big deal"
> in English or Metric terms?
>
> --
> # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
> # 831-336-2558 * * * * * *je...@comix.santa-cruz.ca.us
> #http://802.11junk.com* * * * * * * je...@cruzio.com
> #http://www.LearnByDestroying.com* * * * * * * AE6KS

Woden98 wrote:

> I am just trying to understand the ARP protocol.
>
> Broadcasting ARP request is easy to understand because the sender does
> not know who has the MAC-IP mapping. Receiver broadcasting ARP
> response is not a "big deal" which I mean that the ARP response does
> not look flooding a lot of traffic to the network. If ARP response is
> broadcasted, every host will have a chance to update their mapping
> table so they don't have to send a ARP request any more later on when
> they need it. But why in ARP protocol, the APR response is
> specifically sent back to the the requester only? What is the
> difference?
>
>
>
> On Nov 6, 9:03 pm, Jeff Liebermann <je...@cruzio.com> wrote:
>
>>On Thu, 6 Nov 2008 17:51:45 -0800 (PST), Woden98
>>
>><wgao_perso...@yahoo.com> wrote:
>>
>>>I guess this is a dumb question. Is it a big deal to broadcase the ARP
>>>response to every host in the LAN? Thanks.
>>
>>An ARP broadcast is a broadcast packet, which means it goes all over
>>the network. The ARP
>> who-has IP_address tell source_IP_address
>>packet asks everyone "who has this IP address". Only the holder of
>>the IP address responds with the packet going to the IP address
>>following the "tell". Therefore, the response only goes to the
>>originating IP address, not the entire network.
>>
>>What problem are you trying to solve and what the hell is a "big deal"
>>in English or Metric terms?
>>
>>--
>># Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
>># 831-336-2558 je...@comix.santa-cruz.ca.us
>>#http://802.11junk.com je...@cruzio.com
>>#http://www.LearnByDestroying.com AE6KS
>
>

The ARP response is directed only to the node that made the ARP request
in order to minimize the processing load on other nodes. Simple, eh?
--
Cheers, Bob

Woden98 wrote:
> I am just trying to understand the ARP protocol.
>
> Broadcasting ARP request is easy to understand because the sender does
> not know who has the MAC-IP mapping. Receiver broadcasting ARP
> response is not a "big deal" which I mean that the ARP response does
> not look flooding a lot of traffic to the network. If ARP response is
> broadcasted, every host will have a chance to update their mapping
> table so they don't have to send a ARP request any more later on when
> they need it. But why in ARP protocol, the APR response is
> specifically sent back to the the requester only? What is the
> difference?
>
Perhaps you should try thinking in terms of large networks where the
majority of workstations do not communicate with each other but with
servers. As the majority do not communicate with each other what is the
point in spending cpu time in looking at arp responses and wasting
network time, most arp caches default at 10 or 20 minutes so you would
quickly lose the unwanted info anyway if you had a broadcast response,
you would also have to ensure that the arp cache of each workstation was
sufficiently large enough to hold the data for all the workstations in
the network.