[Info-vax] SOLVED: Re: tcpip gateway question

[Philip Paeps]

Rick Jones <rick.jones2 at hp.com> wrote:
> In comp.protocols.tcp-ip glen herrmannsfeldt <gah at ugcs.caltech.edu> wrote:
> > I wouldn't be surprised if some broadcast replies.  How many update the
> > cache on broadcast requests not destined for them?
>
> Unless a gratuitous ARP happens to qualify as a reply (even though it isn't)
> I don't think that ARP replies are ever sent as anything other than unicast
> frames.

The RFC allows gratuitous arps to be either "requests" or "replies" (actually,
it allows it by not forbidding either, if I remember correctly).  In practice,
most implementations send gratuitous arps as "requests".

I have however encountered embedded devices which send them as "replies" (in
fact the product I was working on decided to crash if that happened, which was
why I looked at the code in the first place :-)).

My feeling is that gratuitous arps should be "special cased" regardless of
whether they say they are a reply or a request.  It's quite easy to imagine a
rogue sender of arp messages filling up a host's arp table by sending a large
number of gratuitous messages.

 - Philip

-- 
Philip Paeps                                    Please don't email any replies
philip at paeps.cx                                     I follow the newsgroup.

  New systems generate new problems.