Subject: Re: dhcpd(8) _cannot_ be completely disabled on an interface
To: der Mouse <mouse@Rodents.Montreal.QC.CA>
From: Andrew Brown <>
List: tech-net
Date: 01/12/2002 00:20:56
>>>> in which case the interface "name" and "address" (which have the
>>>> same lifetime issues as the number)
>>> I don't think so, not if numbers are assigned sequentually at boot
>>> and never repeated.  In practice today, a 32-bit serial number will
>>> never be repeated; a 64-bit probably will never be repeated for the
>>> foreseeable lifetime of NetBSD.
>> While this might be true,
>>         u_short if_index;               /* numeric abbreviation for this if */
>> in practice today 16-bit serial numbers are repeated.
>They are?  I have trouble thinking of any situation not contrived for
>the purpose where 64K interface creates occur without an intervening
>reboot.  Where did you find such?  It's probably worth preserving as a
>stress-test case....

i was thinking the same thing, as my numbers on my laptop never seem
to get above, say, 50 before i reboot.  that includes popping cards
once or twice a day, maybe more, depending on what i'm doing.

then it occurred to me that if, for example, ppp interfaces were
cloning (just as nul, bridge, vlan, stf, faith, gif, gre, and tun
already are), then a poorly configured system where

(1) someone logs in
(2) starts up pppd
(3) pppd allocates itself an interface
(4) pppd fails to establish a connection
(5) destroys the interface and quits

combined with very rapid retry might exceed 64k before the machine
rebooted.  kinda like the isdn bills that some poor sappy customers
used to get from the phone company when they were just getting set up
with isdn dialup.  since the dialup/negotiation/teardown is so much
faster, then had the ability to make roughly one failed call per
second for days before they got around to realizing that things were
wrong.  that's ~200,000 message units (a really high phone bill) and a
lot of (failed) ppp attempts.

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