9 More Discussions You Might Find Interesting
1. Shell Programming and Scripting
How can view log messages between two time frame from /var/log/message or any type of log files.
when logfiles are very big and especially many messages with in few minutes, I would like to display log messages between 5 minute interval.
Could you pls give me the command? (1 Reply)
Discussion started by: johnveslin
1 Replies
2. Solaris
Can anybody please tell me how I can figure out on a solaris server how long it would take a TCP SYN request to timeout before it gets a SYN_ACK back?
Thanks, (3 Replies)
Discussion started by: Pouchie1
3 Replies
3. UNIX for Dummies Questions & Answers
I am using vim version 7.1.314.It don't have syn on.Is there any plug in available for syn on or I have to update the version. (2 Replies)
Discussion started by: karthigayan
2 Replies
4. UNIX for Dummies Questions & Answers
Hi guys,
I have a script that call another, the other displays de message and I can print directly to the flat file, but in one command I am searchig that this message can be displayed in the screen and in the flat file in one command.
I am doing something like this:
var=$(./Example.sh)... (2 Replies)
Discussion started by: pipoca
2 Replies
5. Shell Programming and Scripting
Friends
I have to redirect STDERR messages both to screen and also capture the same in a file.
2 > &1 | tee file works but it also displays the non error messages to file, while i only need error messages.
Can anyone help?? (10 Replies)
Discussion started by: vikashtulsiyan
10 Replies
6. UNIX for Advanced & Expert Users
Please tell me details about terms FIN, ACK, SYN, RST; used in TCP based communication. Also tell me any RFC or other document which tell me details about these terms. (1 Reply)
Discussion started by: mansoorulhaq
1 Replies
7. Shell Programming and Scripting
suppose I have data in a log file in the below format
date|time|name|email|address|SSN
date|time|name|email|address|SSN
date|time|name|email|address|SSN
is it possible to create a search engine which takes input as three filters out of which two filters should be optional?
say i give... (4 Replies)
Discussion started by: wannalearn
4 Replies
8. Linux
Hi all,
A security scanner has been done on a linux server and have found that
The remote host does not discard RCP SYN packets which have the FIN flag set.
It tells that I need to request a patch which I haven't found yet.
I have Red Hat Linux release 7.0 (Guinness)
Kernel 2.2.16-22... (2 Replies)
Discussion started by: bert.n
2 Replies
9. Programming
Hi,
I'm trying to create a RAW TCP SYN packet and send it from one Linux machine to another. I know the packet I have created is well formed and is received by the peer.
Now what I want is to get an ACK for my SYN. I want the peer's Network protocol stack to send me an ACK for that. I know... (17 Replies)
Discussion started by: zampya
17 Replies
mxallowd(1) User Manuals mxallowd(1)
NAME
mxallowd - dynamically whitelist your Mail eXchanger
SYNOPSIS
mxallowd [-d] [-c configfile] [-t whitelist-time] [-p pflog-interface] [-l pcap-filter] [-F] [-s] [-q] [-p] -f fake-mailserver -r real-
mailserver -n queue-num
DESCRIPTION
mxallowd is a daemon which uses libnetfilter_queue (on Linux) or pf and pflog (on BSD) to allow (or deny) connections to a mailserver (or
similar application) if the remote host hasn't connected to a fake daemon before.
This is an improved version of the so-called nolisting (see http://www.nolisting.org/). The assumption is that spammers are not using RFC
2821-compatible SMTP-clients and are sending fire-and-forget spam (directly to the first or second MX-entry without retrying on error).
This direct access is blocked with mxallowd, you'll only get a connection if you retry.
NOTE: It is highly recommended to install nscd (nameserver caching daemon) or a similar software in order to speed-up DNS lookups. Since
version 1.3, DNS lookups are done in a thread (so they don't block the main process), however, on very-high-traffic-sites, mxallowd may
show significantly better overall performance in combination with nscd.
OPTIONS
-b, --no-rdns-whitelist
Disable whitelisting all IP-addresses that have the same RDNS as the connecting one (necessary for google mail)
-c, --config
Specifies an alternative configuration file (instead of /etc/mxallowd.conf)
-t, --whitelist-time
Specify the amount of time (in seconds) until an IP-address will be removed from the whitelist
-s, --stdout
Log to stdout, not to syslog
-q, --quiet
Don't log anything but errors.
-f, --fake-mailserver
Specify which IP-address the fake mailserver has (connecting to it will whitelist you for the real mailserver)
-r, --real-mailserver
Specify which IP-address the real mailserver has
-F, --foreground
Do not fork into background, stay on console
-n, --queue-num (only available when compiled for netfilter_queue)
Specify the queue number which will be used for the netfilter_queue-link. This has to be the same which is specified in the ipta-
bles-rule and it has to be specified, there is no default.
-p, --pflog-interface (only available when compiled for pf)
Specify the pflog(4) interface which you configured in pf(4). The default is pflog0. Also see the pcap-filter-option if you use an
interface which does not only get smtp-traffic.
-l, --pcap-filter (only available when compiled for pf)
Specify the filter for pcap. The default is "port 25". See tcpdump(8) for more information on the filters.
FILES
/etc/mxallowd.conf
System-wide configuration file. Use the long options without the beginning two dashes. For example:
stdout
fake-mailserver 192.168.1.3
fake-mailserver 192.168.1.4
real-mailserver 192.168.1.5
queue-num 23
EXAMPLES FOR NETFILTER
The machine has two IP-addresses. The mailserver only listens on 192.168.1.4, the nameserver returns the mx-records mx1.domain.com
(192.168.1.3) with priority 5 and mx2.domain.com (192.168.1.4) with priority 10.
# modprobe nfnetlink_queue
# iptables -A INPUT -p tcp --dport 25 -m state --state NEW -j NFQUEUE --queue-num 23
# mxallowd -s -F -f 192.168.1.3 -r 192.168.1.4 -n 23
Then open a separate terminal and connect via telnet on your real mailserver. You'll see the connection attempt being dropped. Now connect
to the fake mailserver and watch mxallowd's output. Afterwards, connect to the real mailserver to verify your mailserver is still working.
EXAMPLES FOR PF
The machine has two IP-addresses. The mailserver only listens on 192.168.1.4, the nameserver returns the mx-records mx1.domain.com
(192.168.1.3) with priority 5 and mx2.domain.com (192.168.1.4) with priority 10.
Create a pf.conf like this:
table <mx-white> persist
real_mailserver="192.168.1.4"
fake_mailserver="192.168.1.3"
real_mailserver6="2001:dead:beef::1"
fake_mailserver6="2001:dead:beef::2"
pass in quick log on fxp0 proto tcp from <mx-white> to $real_mailserver port smtp
pass in quick log on fxp0 inet6 proto tcp from <mx-white> to $real_mailserver6 port smtp
block in log on fxp0 proto tcp to { $fake_mailserver $real_mailserver } port smtp
block in log on fxp0 inet6 proto tcp to { $fake_mailserver6 $real_mailserver6 } port smtp
Afterwards, load it and start mxallowd using the following commands:
# pfctl -f /etc/pf.conf
# mxallowd -s -F -f 192.168.1.3 -r 192.168.1.4
Then open a separate terminal and connect via telnet on your real mailserver. You'll see the connection attempt being dropped. Now connect
to the fake mailserver and watch mxallowd's output. Afterwards, connect to the real mailserver to verify your mailserver is still working.
The ruleset for pf is actually longer because pf does more than netfilter on linux -- netfilter passes the packets and lets mxallowd decide
whether to drop/accept whilst pf blocks/passes before even "passing" to mxallowd.
SEE ALSO
iptables(8), pf(4), pflog(4), tcpdump(8)
AUTHOR
Michael Stapelberg <michael+mxallowd at stapelberg dot de>
Linux MARCH 2012 mxallowd(1)