Re: UDP dont fragment bit

From: Jeremie Le Hen (jeremie_at_le-hen.org)
Date: 09/22/05

  • Next message: Robert Watson: "Re: tap devices and DHCP." 
    Date: Thu, 22 Sep 2005 11:50:02 +0200
To: Sten Daniel Sørsdal <lists@wm-access.no>

    Hi,

    > Often there already is need for a tcp connection for authentication,
    > negotiation and so forth.
    >
    > RTT could, among other things, make a discovery process choose how fine
    > the increments/descrements should be.
    >
    > Estimated bandwidth could also help the actual data transport start out
    > with a more situation correct value.
    >
    > However with the abundance of routers modifying TCP MSS correctly
    > incorrectly and the odd chance that the data path of UDP packets is
    > different than TCP packets it wouldnt really give anything necessarily
    > reliable discovery process. And taking advantage of such values could
    > make the process more complex or less reliable.

    This is a rather specific case IMHO. BSD community didn't use to take
    care of such non standard behaviours, AFAIK. What you describe here
    is not really what's currently stated in RFCs.

    I would not be in favor of adding such an option in the FreeBSD kernel
    because, as Robert stated, this doesn't bring anything if not coupled
    with a non-trivial mechanim that could provide the user with ICMP MTU
    events. If one adds this option to the manual page, this will lead
    for sure to have mails emitted on this even list asking for how to
    retrieve those informations. Furthermore, I ought to add that the
    algorithm you described in pseudo-code lacks of robustness because
    of possible network congestion, which means this isn't something one
    would really see in wide use.

    In other words, I think the feature you're calling for is really
    specific to your problem, regarding your current network environnement.
    The misbehaviour of some particular network-fascist ISP should not
    reach the FreeBSD source tree.

    Best regards, 

    -- 
Jeremie Le Hen
< jeremie at le-hen dot org >< ttz at chchile dot org >
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  • Next message: Robert Watson: "Re: tap devices and DHCP."