Re: Arp expire/timeout 2.1.132/2.2pre1

Andi Kleen (ak@muc.de)
04 Jan 1999 18:36:03 +0100


In article <199901041723.UAA22628@ms2.inr.ac.ru>,
kuznet@ms2.inr.ac.ru writes:
> Hello!
>> Still there is the issue that user level protocols can't signal forward
>> process to the kernel. How about adding a socket option that does it
>> for connected sockets to plug this hole?

> It is possible, but I do not believe that this thing is really useful.

> ARP is enough cheap to prefer background pinging to new syscall,
> made in data path. Besides that, it requires, that datagram protocols,
> keeping some state (f.e. DNS) become system dependant.
> This thing has no chances to live.

For DNS it would be overkill I agree, but for other protocols (like Coda
which does bulk transfer over an UDP(?) based RPC protocol in userspace)
it could be useful. Also a system call is still much much cheaper than
sending and receiving an ARP packet, which also introduces "bubbles"
into long running data transfers.

> Well, I think, when this element will appear (or recognized to be useless)
> for IPv6, we will port it back to IPv4.

Is this considered by the working groups?

> What's about this case: using user level notifications in this case
> is not solution. If target does not answer arp, it is broken,
> no advanced tricks will change this fact and any cure is just workaround.
> Increasing timeout is the easiest workaround, at least.

My thinking was just that everything that is possible for a kernel protocol
should be possible for a user level protocol too - no unfair advantage
for the kernel ;)

-Andi

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