Subject: [dhcwg] Max msg size and interface MTU options

From: Ralph Droms <[email-masked]>
Date: Mon, 24 Oct 2005 14:49:38 -0400

Anyone have an opinion about how widely implemented the max msg size
(code 57) and interface MTU (code 26) options are?

- Ralph

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---

From: "David W. Hankins" <[email-masked]>
Date: Thu, 27 Oct 2005 09:26:46 -0700

> (code 57) and interface MTU (code 26) options are?

Trivia from [email-masked] mailing list some months back.  How do
you fingerprint an operating system via dhcp?  Requested options list,
of course.

	class "VendorIdent" {
		match option dhcp-parameter-request-list;
	}

	subclass "VendorIdent" 1:3:6:f:2c:2e:2f:39 {
		set os-ident = "Microsoft Windows 98";
	}

So, Windows 98 is thought to request option 57 (0x39), according to
this data I've been given anyway.

I'm not aware of any that request 26.

I don't happen to have a list of clients that supply different options,
that would be a cool list to have, but I have seen clients that supply
57 even if I can't remember their names now.

Speaking for ISC DHCP, support for 57 is implemented in the server
(adjusting maximum output message size to match), but no value is
configured in options sent to clients.

dhclient also makes no attempt to divine the server's mms, or to provide
one.  If it were given an option 26, it would be able to understand it,
but it would not digest it (ifconfig mtu etc is never issued).

-- 
David W. Hankins		"If you don't do it right the first time,
Software Engineer			you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins
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