Security Basics mailing list archives
AW: Iptables Clues and Advices.
From: "Michael Kluge" <michael.kluge () wundermedia de>
Date: Fri, 11 Apr 2003 10:32:59 +0200
Hi! I think DROP gives indeed some kind of extra security over REJECT. Most scanners are used on networks not on specific hosts. These scanners (like nmap) usually try to ping (icmp or TCP) each host in a network. Only hosts answering are scanned. So if you use DROP in many cases your host will not be found and therefore be no subject of attack. At least it will keep off a lot of script-kiddies. It is true that if you provide any service to the internet, your host CAN be found by portscanning. But it's not true that it WILL necessarily be found by portscanning if you use DROP. If using REJECT it usually will be found! And this is exactly the difference of these two methods and IMHO the best reason to use DROP. A legitimate user won't run into any problems as a legitimate user will only connect to open ports. The only port I use REJECT for, is TCP 113 (ident), because many services (eg. many ftp servers) try to connect to this port. Michael.
-----Ursprüngliche Nachricht----- Von: Jeff Harris [mailto:jharris () tahongawaka nu] Gesendet: Mittwoch, 9. April 2003 20:51 An: security-basics () securityfocus com Betreff: Re: Iptables Clues and Advices. -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 It seems to me that DROP would be used for creating the appearance that your IP isn't in use. If you are providing no services to the internet, then every port should DROP. However, if you have any service, even just a ssh server, someone portscanning you will know that you're there, and a REJECT would be the correct thing to do. Jeff. On Wed, 9 Apr 2003, [iso-8859-1] Julien Royère wrote:I do not agree, DROP drops the connection, no more action. REJECT close a connection by GENERATING a packet. In matter of security they do both the same thing, but if someone spoof an IP, you may respond and annoy someone whose IP has been spoofed. Julien ----- Original Message ----- From: "Jason Dixon" <jasondixon () myrealbox com> To: <gillettdavid () fhda edu> Cc: <security-basics () securityfocus com> Sent: Tuesday, April 08, 2003 6:19 PM Subject: RE: Iptables Clues and Advices.For all the folks who illusion that DROP is more securethan REJECT, Isubmit the following: http://www.chiark.greenend.org.uk/~peterb/network/drop-vs-reject -J. On Mon, 2003-04-07 at 20:03, David Gillett wrote:There is ONE specific case in which I REJECT rather than DROP filtered packets: Sometimes users behind my firewall need to contact an outside POP3 email server. Many such boxes react to such connections by attempting a connection back to the source on port 113 (identd). If I DROP connections to this port, the remote POP3 server will wait for its request to timeout -- and then try again and timeout again, two more times. By REJECTing the connection, I let the server try and fail and try and fail immediately, and so my client's download of mail begins much sooner than it would if I just DROPped those packets. David Gillett-----Original Message----- From: Allan Schon [mailto:allanschon () mckinleymachinery com] Sent: April 7, 2003 08:53 To: security-basics () securityfocus com Subject: RE: Iptables Clues and Advices.it will also result into a mess, because the server will be a hole in space (regarding the blocked ports). And what arethe benefits(if there are any) of this practice?Well, the primary benefit is that attackers scanning for specific open ports in your ip range will never find your machine, if you're dropping connection attempts to the target port. That's a considerable advantage, I think. They can't attack you if they don't know you're there. Are there any specific disadvantages to DROPing? -----Original Message----- From: Andreas Happe [mailto:andreashappe () gmx net] Sent: Saturday, April 05, 2003 5:29 PM To: security-basics () securityfocus com Subject: Re: Iptables Clues and Advices. In article <1049484753.24055.41.camel () unsigned local fr>, Pierre BETOUIN wrote:DROP would be better there because you don't need toprevent attackersthat this port is filtered.it will also result into a mess, because the server will be a hole in space (regarding the blocked ports). And whatare the benefits(if there are any) of this practice? andreas -- I tell them to turn to the study of mathematics, forit is only therethat they might escape the lusts of the flesh. -- Thomas Mann, "The Magic Mountain"-------------------------------------------------------------------SurfControl E-mail Filter puts the brakes on spam, viruses and malicious code. Safeguard your business critical communications. 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- AW: Iptables Clues and Advices. Michael Kluge (Apr 14)