IP4 address conservation method

Thu Jun 6 21:19:26 UTC 2013

On Thu, Jun 6, 2013 at 3:00 PM, Bjørn Mork <bjorn at mork.no> wrote:
> William Herrin <bill at herrin.us> writes:
>> On Wed, Jun 5, 2013 at 6:25 PM, Ricky Beam <jfbeam at gmail.com> wrote:
>>> I won't argue against calling Linux "wrong".  However, the linux way of
>>> dealing with ARP is well tuned for "host" and not "router" duty.
>>
>> I love Linux and use it throughout my work but I can't tell you the
>> number of times its ARP behavior has bitten me. If you send a packet
>> to a VIP on a Linux box and it doesn't have an arp entry for the
>> default gateway, the Linux box will send an arp request... with the
>> vip as the source. That is just wrong. Wrong, wrong, wrong. Use the
>> damn interface IP when you arp for something on that interface. If the
>> router doesn't happen to like the bad arp (since the VIP isn't on the
>> router's LAN) the router will ignore it. And your service will merrily
>> pop up and down depending on whether the Linux box has any traffic to
>> originate.
>
> Did you try setting sys.net.ipv4.conf.all.arp_announce=2 ?

Yes, of course I changed the sysctl. Yes of course that worked. Every
time I've run in to the problem. On server after server after server.

> Yes, the system default may be tuned for host/desktop usage

No, it doesn't default to reasonable desktop settings for ARP... it
defaults to a version of wrong that on a desktop with one NIC and one
IP doesn't happen to break anything. It'd be nice if it defaulted to
RFC compliant instead and let the few folks with wacky needs move it
off the standard behavior.

-Bill

-- 
William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
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