Date: Wed, 6 Mar 2002 21:50:41 +0100 From: Thomas Seck <tmseck@netcologne.de> To: freebsd-stable@FreeBSD.ORG Subject: Re: ppp and growing ip alias list Message-ID: <20020306205041.GA470@laurel.seck.home> In-Reply-To: <LMEMIKHGPPEEMMMMGIENEEBFEDAA.manek@ecst.csuchico.edu> References: <LMEMIKHGPPEEMMMMGIENEEBFEDAA.manek@ecst.csuchico.edu>
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# Sameer R. Manek (manek@ecst.csuchico.edu):
> On my 4.5-stable box, I've noticed what I think is a bug with ppp.
Nope,
this is a feature. It is very useful when you get only dynamic IPs and
use the -auto option to re-establish the connection after a disconnect
or a "close-on-idle" (which is what I use).
This feature works around the problem that the IP packet that triggers
the opening of a closed link is sent with the address that was assigned
to the interface the last time it was up. There is a good chance that
the new address of the interface will be different from the address
which is written into the packet. Thus, replies to this packet will
never get back to you so the sending application has to resend them
after a timeout. This is usually not a problem should the application
use UDP. A dial-up connection is usually brought up by DNS lookups via
UDP.
You will see the problem when you run a caching DNS resolver on your
machine such as dnscache from the net/djbdns port. When the DNS requests
are answered by your resolver without opening the dial-up link, an
application that wants to establish a TCP connection will bring the
connection up with the first TCP SYN packet. The handshake is thus
initialized with a packet that has a wrong sender address and will
obviously fail. You will notice ugly timeouts.
The "iface-alias" in conjunction with "nat enable yes" will solve this
problem. See ppp(8) for more information about this.
--Thomas
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