From owner-freebsd-security Tue Aug 22 8:17:28 2000 Delivered-To: freebsd-security@freebsd.org Received: from world.std.com (world-f.std.com [199.172.62.5]) by hub.freebsd.org (Postfix) with ESMTP id 9908937B43C for ; Tue, 22 Aug 2000 08:17:26 -0700 (PDT) Received: (from lowell@localhost) by world.std.com (8.9.3/8.9.3) id LAA16210; Tue, 22 Aug 2000 11:17:26 -0400 (EDT) To: freebsd-security@freeBSD.org Subject: Re: icmptypes References: <20000821180351.H57333@jade.chc-chimes.com> <20000821181825.I57333@jade.chc-chimes.com> From: Lowell Gilbert Date: 22 Aug 2000 11:17:25 -0400 In-Reply-To: billf@chimesnet.com's message of 22 Aug 2000 00:18:46 +0200 Message-ID: Lines: 28 X-Mailer: Gnus v5.5/Emacs 20.2 Sender: owner-freebsd-security@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org billf@chimesnet.com (Bill Fumerola) writes: > On Mon, Aug 21, 2000 at 03:16:03PM -0700, Rodney W. Grimes wrote: > > > > example from memory: > > > # ipfw add unreach filter-prohib icmp from any to any icmptypes 0,8 > > > > The 8 case would be okay, but returning an icmp unreach for an icmp echo > > reply would be a violation of the protocol spec. I would recomend > > against it. > > Yes, unreaching 0 would be nonsense I suppose. > > On a side note, RFC and protocol blah blah is nice, but sometimes you > just have to drop packets and break spec if the machine is a target. Dropping packets is never a violation of the protocol spec. Returning ICMP "unreachable" errors in response to other ICMP packets would be. This is an important distinction. [It's also what Rodney Grimes actually said.] > If this is being used as a border firewall or some such, then I would > certainly heed Rod's advice on being careful what to break. For a single > machine, I'd be less worried. The gains, however, are fairly small. And some things *will* break. At a very minimum, allow echo replies (possibly via stateful tracking), dest unreachable, TTL exceeded, and header error. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-security" in the body of the message