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    SubjectRe: ECN: Clearing the air (fwd)
    On Sun, 28 Jan 2001, jamal wrote:
    > On Sun, 28 Jan 2001, James Sutherland wrote:
    >
    > > I'm sure we all know what the IETF is, and where ECN came from. I haven't
    > > seen anyone suggesting ignoring RST, either: DM just imagined that,
    > > AFAICS.
    >
    > The email was not necessarily intended for you. You just pulled the pin.
    > There were people who made the suggestion that TCP should retry after a
    > RST because it "might be an anti-ECN path"

    That depends what you mean by "retry"; I wanted the ability to attempt a
    non-ECN connection. i.e. if I'm a mailserver, and try connecting to one of
    Hotmail's MX hosts with ECN, I'll get RST every time. I would like to be
    able to retry with ECN disabled for that connection.

    > > The one point I would like to make, though, is that firewalls are NOT
    > > "brain-damaged" for blocking ECN: according to the RFCs governing
    > > firewalls, and the logic behind their design, blocking packets in an
    > > unknown format (i.e. with reserved bits set) is perfectly legitimate.
    >
    > I dont agree that unknown format == reserved. I think it is bad design to
    > assume that. You may be forgiven if you provide the operator
    > opportunities to reset your assumptions via a config option.
    > It has nothing to do with a paranoia setting, just a bad design. Nothing
    > legit about that.

    On the contrary: rejecting weird-looking traffic is perfectly legit. I
    agree RST is the wrong response, but it's too late to tell Cisco that
    now...

    > > Yes,
    > > those firewalls should be updated to allow ECN-enabled packets
    > > through. However, to break connectivity to such sites deliberately just
    > > because they are not supporting an *experimental* extension to the current
    > > protocols is rather silly.
    >
    > This is the way it's done with all protocols. or i should say the way it
    > used to be done. How do you expect ECN to be deployed otherwise?

    The current versions of these firewalls handle ECN OK. I just want Linux
    to degrade gracefully when unable to use ECN: it will be a while before
    all these firewalls have gone.

    > The internet is a form of organized chaos, sometimes you gotta make
    > these type of decisions to get things done. Imagine the joy _most_
    > people would get flogging all firewall admins who block all ICMP.

    Blocking out ICMP doesn't bother me particularly. I know they should be
    selective, but it doesn't break anything essential.

    > There is nothing silly with the decision, davem is simply a modern day
    > internet hero.

    No. If it were something essential, perhaps, but it's just a minor
    performance tweak to cut packet loss over congested links. It's not
    IPv6. It's not PMTU. It's not even very useful right now!


    James.

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