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Date:      Sat, 3 Aug 2002 22:32:49 -0500 (EST)
From:      "Michael L. Squires" <mikes@12-222-67-235.client.insightBB.com>
To:        Bri <brian@ukip.com>
Cc:        FreeBSD Stable <freebsd-stable@freebsd.org>
Subject:   Re: dhcp problems with my ISP
Message-ID:  <200208040332.g743Wn5c089555@12-222-67-235.client.insightBB.com>
In-Reply-To: <NEBBKKNOEKKNLLNMEOHFAEBFIKAA.brian@ukip.com> "from Bri at Aug 3, 2002 11:12:12 am"

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> Hi I have a Cable and have a Cable Modem for my internet connection of which
> you use dhcp to obtain an IP address great but this only seems to work
> successfully on a Windows machine I've registered all the other mac
> addresses of unix boxes and Apple macs I have and they seem to have alot of
> difficulty obtaining IP addresses. Especially the UNIX machines which run
> FreeBSD 4.5-RELEASE or 5.0-CURRENT on sparc64 at the moment the sparc64 box
> which is a Sun Ultra 5 which is the worst for detecting an IP with dhclient.
> 
> What I would really like to know is what does the windows dhcp do
> differently than say dhclient.

Some cable companies have started placing DHCP servers very far away from
the networks they serve (more than 50 hops, in one case).  This does not
cause major problems with Windows since they allow 128 hops, but does
cause problems with the *NIXes which use a smaller number (16?) hops.

The quick fix is to recompile dhcp (/usr/src/contrib/isc-dhcp and
increase the "ttl" from 16 to something bigger.  The note I saw elsewhere
said 128 was a reasonable figure.

This occurred for a number of ATTBI BSD users elsewhere about 6/17.  My memory
is that this was discussed on www.dslreports.com and on some of the LINUX
newsgroups.

The suggested changes are to change line 155 (approx) in 

/usr/src/contrib/isc-dhcp/common/packet.c from

	ip.ip_tos = IPTOS_LOWDELAY;

to

	ip.ip_tos = 0;

and line 160 (approx)

	ip.ip_ttl = 16;

to

	ip.ip_ttl = 128;

This assumes, of course, that you've downloaded source for that part of the
OS at least.

Mike Squires

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