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• How can an application (like Firefox) be forced to use a certain network interface?

  - by Lekensteyn

  I've two interfaces: eth0 and wlan0 on a notebook. Possible use cases: eth0 grants me Internet access, and wlan0 is currently connected to a router which does not have Internet-connectivity. For development purposes, I need to connect to the wlan0 by default, but use eth0 for surfing eth0 and wlan0 are both connected to the Internet. For a torrent application, eth0 should be used for speed, but for portability of the notebook, SSH should have a connection over wlan0 eth0 is a wire connection, wlan0 is a wireless one. Sensible data should be transferred over eth0, but other traffic can go over wlan0 as well. Is there a way to force applications (like nc.traditional or firefox) to use a certain network interface? A wrapper like example-wrapper eth0 program is fine too if such program exist. It would be nice if it could configured within Firefox (in runtime). I'd like to avoid IPTables solutions if possible.

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• How can an application (like Firefox) be forced to use a certain network interface?

  - by Lekensteyn

  I've two interfaces: eth0 and wlan0 on a notebook. Possible use cases: eth0 grants me Internet access, and wlan0 is currently connected to a router which does not have Internet-connectivity. For development purposes, I need to connect to the wlan0 by default, but use eth0 for surfing eth0 and wlan0 are both connected to the Internet. For a torrent application, eth0 should be used for speed, but for portability of the notebook, SSH should have a connection over wlan0 eth0 is a wire connection, wlan0 is a wireless one. Sensible data should be transferred over eth0, but other traffic can go over wlan0 as well. Is there a way to force applications (like nc.traditional or firefox) to use a certain network interface? A wrapper like example-wrapper eth0 program is fine too if such program exist. It would be nice if it could configured within Firefox (in runtime). I'd like to avoid IPTables solutions if possible.

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• Webmin no longer works - connection rejected

  - by Omeed

  I've had webmin installed on my 12.04 server and everything has been fine until recently. Now when I navigate to https:// myip:10000 I get a message saying the connection attempt is rejected. The last thing I did was set up a cron job to start utorrent webUI. I tried reinstalling but no change. When I check with netstat I see a webmin entrance on port 10000. I've also reset the iptables and allowed everything. I'm at a loss as to what to do now.

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• Is it possible to configure Ubuntu as a software firewall?

  - by user3215

  I have some systems running on Ubuntu in the private IP range 192.168.2.0-255 . These systems are connected to a switch and the switch is connected to the ISP's modem. Neither the switch nor the modem support firewall options. I don't have any firewall device and I'm not willing to individually configure firewalls on all the systems (via gui/iptables). Is it possible to make an Ubuntu system into something like a software firewall, so that all the traffic/packets sent to or from the WAN(internet) would be allowed/denied based on its firewall rules?

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• What are your recommended tools and frameworks for network development on Linux?

  - by Vivek Sharma

  What are your favourite network-tools, which you use to troubleshoot or design (as in conceptualize) your network-application code. Ethereal/Wireshark Nmap any particular simulators (e.g. ns) any special purpose sniffer any particular frameworks, (e.g. iptables) I am looking at must have, and good/advantage to have tools/framework in ones profile/skill set. I think Wireshark and Nmap are must haves.

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• MySQL server address binding fails in Ubuntu server

  - by SoulReaver

  I am using MySQL server on Ubuntu 10.04 and after changing the bind-address from 127.0.0.1 to my webserver IP in /etc/mysql/my.cnf the mysql server fails to load. Any clues will be highly appreciated! I have tried disabling iptables but useless Thanks,

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• Redirect-gateway def1

  - by John

  I have setup OpenVPN on my server, and I am able to connect to it just fine, and browse the web, etc, from the client box. If I set the following option in the client config, I can no longer browse the web via domain name: redirect-gateway def1 On the server, I have run the following command: iptables -t nat -s 10.8.0.0/24 -A POSTROUTING -j SNAT --to myserver'sIP but that hasn't changed anything. Can anyone help suggest something?

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• Wireless AAA for a small, bandwidth-limited hotel.

  - by Anthony Hiscox

  We (the tech I work with and myself) live in a remote northern town where Internet access is somewhat of a luxury, and bandwidth is quite limited. Here, overage charges ranging from few hundreds, to few thousands of dollars a month, is not uncommon. I myself incur regular monthly charges just through my regular Internet usage at home (I am allowed 10G for $60CAD!) As part of my work, I have found myself involved with several hotels that are feeling this. I know that I can come up with something to solve this problem, but I am relatively new to system administration and I don't want my dreams to overcome reality. So, I pass these ideas on to you, those with much more experience than I, in hopes you will share some of your thoughts and concerns. This system must be cost effective, yes the charges are high here, but the trust in technology is the lowest I've ever seen. Must be capable of helping client reduce their usage (squid) Allow a limited (throughput and total usage) amount of free Internet, as this is often franchise policy. Allow a user to track their bandwidth usage Allow (optional) higher speed and/or usage for an additional charge. This fee can be obtained at the front desk on checkout and should not require the use of PayPal or Credit Card. Unfortunately some franchises have ridiculous policies that require the use of a third party remote service to authenticate guests to your network. This means WPA is out, and it also means that I do not auth before Internet usage, that will be their job. However, I do require the ABILITY to perform authentication for Internet access if a hotel does not have this policy. I will still have to track bandwidth (under a guest account by default) and provide the same limiting, however the guest often will require a complete 'unlimited' access, in terms of existence, not throughput. Provide firewalling capabilities for hotels that have nothing, Office, and Guest network segregation (some of these guys are running their office on the guest network, with no encryption, and a simple TOS to get on!) Prevent guests from connecting to other guests, however provide a means to allow this to happen. IE. Each guest connects to a page and allows the other guest, this writes a iptables rule (with python-netfilter) and allows two rooms to play a game, for instance. My thoughts on how to implement this. One decent box (we'll call it a router now) with a lot of ram, and 3 NIC's: Internet Office Guests (AP's + In Room Ethernet) Router Firewall Rules Guest can talk to router only, through which they are routed to where they need to go, including Internet services. Office can be used to bridge Office to Internet if an existing solution is not in place, otherwise, it simply works for a network accessible web (webmin+python-webmin?) interface. Router Software: OpenVZ provides virtualization for a few services I don't really trust. Squid, FreeRADIUS and Apache. The only service directly accessible to guests is Apache. Apache has mod_wsgi and django, because I can write quickly using django and my needs are low. It also potentially has the FreeRADIUS mod, but there seems to be some caveats with this. Firewall rules are handled on the router with iptables. Webmin (or a custom django app maybe) provides abstracted control over any features that the staff may need to access. Python, if you haven't guessed it's the language I feel most comfortable in, and I use it for almost everything. And finally, has this been done, is it a overly massive project not worth taking on for one guy, and/or is there some tools I'm missing that could be making my life easier? For the record, I am fairly good with Python, but not very familiar with many other languages (I can struggle through PHP, it's a cosmetic issue there). I am also an avid linux user, and comfortable with config files and command line. Thank you for your time, I look forward to reading your responses. Edit: My apologies if this is not a Q&A in the sense that some were expecting, I'm just looking for ideas and to make sure I'm not trying to do something that's been done. I'm looking at pfSense now as a possible start for what I need.

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• virturalmin webmin dose not respond

  - by Miranda

  I have installed Virtualmin on a CentOS remote server, but it dose not seem to work https://115.146.95.118:10000/ at least the Webmin page dose not work. I have opened those ports http ALLOW 80:80 from 0.0.0.0/0 ALLOW 443:443 from 0.0.0.0/0 ssh ALLOW 22:22 from 0.0.0.0/0 virtualmin ALLOW 20000:20000 from 0.0.0.0/0 ALLOW 10000:10009 from 0.0.0.0/0 And restarting Webmin dose not solve it: /etc/rc.d/init.d/webmin restart Stopping Webmin server in /usr/libexec/webmin Starting Webmin server in /usr/libexec/webmin And I have tried to use Amazon EC2 this time, still couldn't get it to work. http://ec2-67-202-21-21.compute-1.amazonaws.com:10000/ [ec2-user@ip-10-118-239-13 ~]$ netstat -an | grep :10000 tcp 0 0 0.0.0.0:10000 0.0.0.0:* LISTEN udp 0 0 0.0.0.0:10000 0.0.0.0:* [ec2-user@ip-10-118-239-13 ~]$ sudo iptables -L -n Chain INPUT (policy ACCEPT) target prot opt source destination ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:20 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:21 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:53 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:20000 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:10000 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:443 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:993 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:143 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:995 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:110 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:20 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:21 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:53 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:587 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:25 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:22 Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination Since I need more than 10 reputation to post image, you can find the screenshots of the security group setting at the Webmin Support Forum. I have tried: sudo iptables -A INPUT -p tcp -m tcp --dport 10000 -j ACCEPT It did not change anything. [ec2-user@ip-10-118-239-13 ~]$ sudo yum install openssl perl-Net-SSLeay perl-Crypt-SSLeay Loaded plugins: fastestmirror, priorities, security, update-motd Loading mirror speeds from cached hostfile * amzn-main: packages.us-east-1.amazonaws.com * amzn-updates: packages.us-east-1.amazonaws.com amzn-main | 2.1 kB 00:00 amzn-updates | 2.3 kB 00:00 Setting up Install Process Package openssl-1.0.0j-1.43.amzn1.i686 already installed and latest version Package perl-Net-SSLeay-1.35-9.4.amzn1.i686 already installed and latest version Package perl-Crypt-SSLeay-0.57-16.4.amzn1.i686 already installed and latest version Nothing to do [ec2-user@ip-10-118-239-13 ~]$ nano /etc/webmin/miniserv.conf GNU nano 2.0.9 File: /etc/webmin/miniserv.conf port=10000 root=/usr/libexec/webmin mimetypes=/usr/libexec/webmin/mime.types addtype_cgi=internal/cgi realm=Webmin Server logfile=/var/webmin/miniserv.log errorlog=/var/webmin/miniserv.error pidfile=/var/webmin/miniserv.pid logtime=168 ppath= ssl=1 env_WEBMIN_CONFIG=/etc/webmin env_WEBMIN_VAR=/var/webmin atboot=1 logout=/etc/webmin/logout-flag listen=10000 denyfile=\.pl$ log=1 blockhost_failures=5 blockhost_time=60 syslog=1 session=1 server=MiniServ/1.585 userfile=/etc/webmin/miniserv.users keyfile=/etc/webmin/miniserv.pem passwd_file=/etc/shadow passwd_uindex=0 passwd_pindex=1 passwd_cindex=2 passwd_mindex=4 passwd_mode=0 preroot=virtual-server-theme passdelay=1 sessiononly=/virtual-server/remote.cgi preload= mobile_preroot=virtual-server-mobile mobile_prefixes=m. mobile. anonymous=/virtualmin-mailman/unauthenticated=anonymous ssl_cipher_list=ECDHE-RSA-AES256-SHA384:AES256-SHA256:AES256-SHA256:RC4:HIGH:MEDIUM:+TLSv1:!MD5:!SSLv2:+SSLv3:!ADH:!aNULL:!eNULL:!NULL:!DH:!ADH:!EDH:!AESGCM

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• Ubuntu 10.04: OpenVZ Kernel and pure-ftpd issues on HOST (no guest setup yet)

  - by Seidr

  After compiling and installing the OpenVZ flavour of kernel under Ubuntu 10.04, I am unable to browse to certain directories when connecting to the pure-ftpd server. The clients are dropping into PASSIVE mode, which is fine. This behaviour was happening before the change of kernel, however now when I browse to certain directories the connection just gets dropped. This only happens with a few directories under one login (web in specific), where as with another login it happens as soon as I connect. I've got the nf_conntrack_ftp kernel module installed (required to keep track of passive FTP connections as I understand, and an alias of the ip_conntrack_ftp module), however this has provided no alleviation of my problem. This module was actually required upon initial setup of my OS to get passive FTP working correctly, however when I compiled the OpenVZ kernel a lot of these modules were missing (iptables, conntrack etc). I recompiled the kernel with the missing modules, but to no effect. I've turned verbosity for the pure-ftpd server up, and still no clues have been spotted in either syslog or the transfer log. Neither did an strace provide any clues (that I could discern anyway) - although one strange thing is both in the output to the client and in the strace I notice that it does infact probe the directory and return the number of matches - it just fails after that. One more thing to mention is that if I FTP using the same credentials locally, everything works fine. This suggests that it is in fact an issue with either the conntrack_ftp module not functioning as expected, or a deeper networking issue. The Kernel was compiled and installed following the instructions at https://help.ubuntu.com/community/OpenVZ - bar the changes to the Kernel configuration (such as add iptables as a module). Below is an example of the log sent to the data (under FileZilla). Status: Resolving address of xxxx.co.uk Status: Connecting to 78.46.xxx.xxx:21... Status: Connection established, waiting for welcome message... Response: 220---------- Welcome to Pure-FTPd [privsep] [TLS] ---------- Response: 220-You are user number 4 of 10 allowed. Response: 220-Local time is now 08:52. Server port: 21. Response: 220-This is a private system - No anonymous login Response: 220-IPv6 connections are also welcome on this server. Response: 220 You will be disconnected after 15 minutes of inactivity. Command: USER xxx Response: 331 User xxx OK. Password required Command: PASS ******** Response: 230-User xxx has group access to: client1 sshusers Response: 230 OK. Current restricted directory is / Command: OPTS UTF8 ON Response: 200 OK, UTF-8 enabled Status: Connected Status: Retrieving directory listing... Command: PWD Response: 257 "/" is your current location Status: Directory listing successful Status: Retrieving directory listing... Command: CWD /web Response: 250 OK. Current directory is /web Command: TYPE I Response: 200 TYPE is now 8-bit binary Command: PORT 10,0,2,30,14,143 Response: 500 I won't open a connection to 10.0.2.30 (only to 188.220.xxx.xxx) Command: PASV Response: 227 Entering Passive Mode (78,46,79,147,234,110) Command: MLSD Response: 150 Accepted data connection Response: 226-ASCII Response: 226-Options: -a -l Response: 226 57 matches total Error: Could not read from transfer socket: ECONNRESET - Connection reset by peer Error: Failed to retrieve directory listing Any suggestions please? I'm willing to try anything!

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• Centos 7. Freeradius fails to start on boot

  - by Alex

  I was messing around with FreeRADIUS and MySQL (MariaDB) and it seems FreeRADIUS service can't start properly on startup. But it starts fine using root user or in debug mode (radiusd -X) and works just fine! Debug mode shows no errors. systemctl command shows that radiusd.service has failed to start. /var/log/messages output: Aug 21 15:52:29 nexus-test systemd: Starting The Apache HTTP Server... Aug 21 15:52:29 nexus-test systemd: Starting MariaDB database server... Aug 21 15:52:29 nexus-test systemd: Starting FreeRADIUS high performance RADIUS server.... Aug 21 15:52:29 nexus-test systemd: Started OpenSSH server daemon. Aug 21 15:52:29 nexus-test mysqld_safe: 140821 15:52:29 mysqld_safe Logging to '/var/log/mariadb/mariadb.log'. Aug 21 15:52:29 nexus-test mysqld_safe: 140821 15:52:29 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql Aug 21 15:52:30 nexus-test systemd: Started Postfix Mail Transport Agent. Aug 21 15:52:30 nexus-test avahi-daemon[604]: Registering new address record for fe80::250:56ff:fe85:e4af on eth0.*. Aug 21 15:52:30 nexus-test systemd: radiusd.service: control process exited, code=exited status=1 Aug 21 15:52:30 nexus-test systemd: Failed to start FreeRADIUS high performance RADIUS server.. Aug 21 15:52:30 nexus-test systemd: Unit radiusd.service entered failed state. Aug 21 15:52:31 nexus-test kdumpctl: kexec: loaded kdump kernel Aug 21 15:52:31 nexus-test kdumpctl: Starting kdump: [OK] Aug 21 15:52:31 nexus-test systemd: Started Crash recovery kernel arming. Aug 21 15:52:31 nexus-test systemd: Started The Apache HTTP Server. Aug 21 15:52:31 nexus-test systemd: Started MariaDB database server. /var/log/radius/radius.log output: Thu Aug 21 15:24:16 2014 : Info: rlm_sql (sql): Driver rlm_sql_mysql (module rlm_sql_mysql) loaded and linked Thu Aug 21 15:24:16 2014 : Info: rlm_sql (sql): Attempting to connect to database "radius" Thu Aug 21 15:24:16 2014 : Info: rlm_sql (sql): Opening additional connection (0) Thu Aug 21 15:24:16 2014 : Error: rlm_sql_mysql: Couldn't connect socket to MySQL server radius@localhost:radius Thu Aug 21 15:24:16 2014 : Error: rlm_sql_mysql: Mysql error 'Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)' Thu Aug 21 15:24:16 2014 : Error: rlm_sql (sql): Opening connection failed (0) Thu Aug 21 15:24:16 2014 : Error: /etc/raddb/mods-enabled/sql[47]: Instantiation failed for module "sql" After seeing this I tried to replicate the problem, killed mariadb.service and started to run debug mode again. And it spits out the same problem as in the radius.log. I tried disabling iptables and firewalld and rebooting, but no luck: systemctl disable iptables systemctl disable firewalld So maybe the problem is in the process startup order or delay of some kind. Maybe FreeRADIUS's SQL module can't connect to not yet started MariaDB? If it, how can I fix this? In earlier versions of RHEL/CENTOS I know you easily see service start order in like rc.d or stuff, now IDK. I am new to this fancy "systemd", "systemctl", "firewalld" stuff Centos 7 introduced so sorry I'm a little bit confused. Also this new FreeRADIUS 3 structure... PS. MariaDB is enabled on startup, credentials in FR DB configuration are correct A little update: cat /etc/systemd/system/multi-user.target.wants/radiusd.service output: [Unit] Description=FreeRADIUS high performance RADIUS server. After=syslog.target network.target [Service] Type=forking PIDFile=/var/run/radiusd/radiusd.pid ExecStartPre=-/bin/chown -R radiusd.radiusd /var/run/radiusd ExecStartPre=/usr/sbin/radiusd -C ExecStart=/usr/sbin/radiusd -d /etc/raddb ExecReload=/usr/sbin/radiusd -C ExecReload=/bin/kill -HUP $MAINPID [Install] WantedBy=multi-user.target

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• How Hacker Can Access VPS CentOS 6 content?

  - by user2118559

  Just want to understand. Please, correct mistakes and write advices Hacker can access to VPS: 1. Through (using) console terminal, for example, using PuTTY. To access, hacker need to know port number, username and password. Port number hacker can know scanning open ports and try to login. The only way to login as I understand need to know username and password. To block (make more difficult) port scanning, need to use iptables configure /etc/sysconfig/iptables. I followed this https://www.digitalocean.com/community/articles/how-to-setup-a-basic-ip-tables-configuration-on-centos-6 tutorial and got *nat :PREROUTING ACCEPT [87:4524] :POSTROUTING ACCEPT [77:4713] :OUTPUT ACCEPT [77:4713] COMMIT *mangle :PREROUTING ACCEPT [2358:200388] :INPUT ACCEPT [2358:200388] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [2638:477779] :POSTROUTING ACCEPT [2638:477779] COMMIT *filter :INPUT DROP [1:40] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [339:56132] -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT -A INPUT -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROP -A INPUT -p tcp -m tcp ! --tcp-flags FIN,SYN,RST,ACK SYN -m state --state NEW -j DROP -A INPUT -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,SYN,RST,PSH,ACK,URG -j DROP -A INPUT -i lo -j ACCEPT -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT -A INPUT -p tcp -m tcp --dport 110 -j ACCEPT -A INPUT -p tcp -m tcp --dport 22 -j ACCEPT -A INPUT -s 11.111.11.111/32 -p tcp -m tcp --dport 22 -j ACCEPT -A INPUT -p tcp -m tcp --dport 21 -j ACCEPT -A INPUT -s 11.111.11.111/32 -p tcp -m tcp --dport 21 -j ACCEPT COMMIT Regarding ports that need to be opened. If does not use ssl, then seems must leave open port 80 for website. Then for ssh (default 22) and for ftp (default 21). And set ip address, from which can connect. So if hacker uses other ip address, he can not access even knowing username and password? Regarding emails not sure. If I send email, using Gmail (Send mail as: (Use Gmail to send from your other email addresses)), then port 25 not necessary. For incoming emails at dynadot.com I use Email Forwarding. Does it mean that emails “does not arrive to VPS” (before arriving to VPS, emails are forwarded, for example to Gmail)? If emails does not arrive to VPS, then seems port 110 also not necessary. If use only ssl, must open port 443 and close port 80. Do not understand regarding port 3306 In PuTTY with /bin/netstat -lnp see Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN 992/mysqld As understand it is for mysql. But does not remember that I have opened such port (may be when installed mysql, the port is opened automatically?). Mysql is installed on the same server, where all other content. Need to understand regarding port 3306 2. Also hacker may be able access console terminal through VPS hosting provider Control Panel (serial console emergency access). As understand only using console terminal (PuTTY, etc.) can make “global” changes (changes that can not modify with ftp). 3. Hacker can access to my VPS exploiting some hole in my php code and uploading, for example, Trojan. Unfortunately, faced situation that VPS was hacked. As understand it was because I used ZPanel. On VPS ( \etc\zpanel\panel\bin) ) found one php file, that was identified as Trojan by some virus scanners (at virustotal.com). Experimented with the file on local computer (wamp). And appears that hacker can see all content of VPS, rename, delete, upload etc. From my opinion, if in PuTTY use command like chattr +i /etc/php.ini then hacker could not be able to modify php.ini. Is there any other way to get into VPS?

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• Are spurious TCP connections on port 53 a problem?

  - by Darren Greaves

  I run a server which amongst other things uses tinydns for DNS and axfrdns for handling transfer requests from our secondary DNS (another system). I understand that tinydns uses port 53 on UDP and axfrdns uses port 53 on TCP. I've configured axfrdns to only allow connections from my agreed secondary host. I run logcheck to monitor my logs and every day I see spurious connections on port 53 (TCP) from seemingly random hosts. They usually turn out to be from ADSL connections. My question is; are these innocent requests or a security risk? I am happy to block repeat offenders using iptables but don't want to block innocent users of one of the websites I host. Thanks, Darren.

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• james - mail server DNS configuration

  - by Chaitanya

  hi, I am setting up james mail server. I installed James and added in the config.xml added the servername as mydomain.com. In the DNS for mydomain.com, I have created a A-record, say mx.mydomain.com, which corresponds to the ipaddress of the above mail server machine. Then added mx.mydomain.com as MX record for mydomain.com. In James, I have created a new user test. From the user I have sent a mail to my gmail account. I see that the mail is accepted and the mail is in outgoing folder of James. But it's not relay to the gmail server. In the config.xml of James, I have added 8.8.8.8 and 8.8.4.4 as the dns server addresses, which are public DNS servers hosted by Google. IPTables on the machine is stopped. Thanks for your help!

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• diagnostic multicast issue using wireshark

  - by Abruzzo Forte e Gentile

  I have a network that is setup for multicast traffic. My setup is the following -Machine A : a server generates multicast traffic. -Machine A : few clients subscribing to that multicast traffic -Machine B : few clients subscribing to that multicast traffic # Address I am using IP : 239.193.0.21 PORT: 20401 The clients in machine A , even if they join the group (I can see IGMP messages through wireshark), don't receive any data while (and this is the funny part) machine B,C and D receive everything. I sorted that issue by completely disabling Linux firewall. Before doing that, I enabled the multicast on the firwall ('reject all'). iptables -A INPUT -m addrtype --src-type MULTICAST -j ACCEPT My question is the following: what I can check in wireshark that can help me in spot such firewall issues in the futures? For TCP/IP I realize by using ping and looking at ICMP packets rejected. What I can check/monitor for multicast? I am using LInux/Red-Hat Enterprise 6.2

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• Server Security

  - by mahatmanich

  I want to run my own root server (directly accessible from the web without a hardware firewall) with debian lenny, apache2, php5, mysql, postfix MTA, sftp (based on ssh) and maybe dns server. What measures/software would you recomend, and why, to secure this server down and minimalize the attack vector? Webapplications aside ... This is what I have so far: iptables (for gen. packet filtering) fail2ban (brute force attack defense) ssh (chang default, port disable root access) modsecurity - is really clumsy and a pain (any alternative here?) ?Sudo why should I use it? what is the advantage to normal user handling thinking about greensql for mysql www.greensql.net is tripwire worth looking at? snort? What am I missing? What is hot and what is not? Best practices? I like "KISS" - Keep it simple secure, I know it would be nice! Thanks in advance ...

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• Linux, some packets are not being NAT

  - by user70932

  Hi, I'm trying to NAT HTTP traffic, I'm new to this and facing some issues. What i'm trying to do is NAT client HTTP requests to a webserver. CLIENT - NAT BOX - WEBSERVER When the client open the IP of the NAT BOX, the request should be pass to the web server. But I'm getting "HTTP request sent, awaiting response..." and then wait serveral minutes before the request is done. Looking at the tcpdump output, it looks like the first Syn packet on (10:48:54) is being NAT but not the second, third, fourth... ACK or PSH packets, and wait until (10:52:04) it starts NAT again on the ACK packet. The iptables command I'm using is: iptables -t nat -A PREROUTING -p tcp -i eth0 --dport 80 \ -j DNAT --to-destination WEBSERVER I'm wondering what could have caused this behavior? Thanks alot. 10:48:54.907861 IP (tos 0x0, ttl 49, id 16395, offset 0, flags [DF], proto: TCP (6), length: 48) CLIENT.61736 > NATBOX.http: S, cksum 0x6019 (correct), 1589600740:1589600740(0) win 5840 <mss 1460,nop,wscale 8> 10:48:54.907874 IP (tos 0x0, ttl 48, id 16395, offset 0, flags [DF], proto: TCP (6), length: 48) CLIENT.61736 > WEBSERVER.http: S, cksum 0xb5d7 (correct), 1589600740:1589600740(0) win 5840 <mss 1460,nop,wscale 8> 10:48:55.102696 IP (tos 0x0, ttl 49, id 16397, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x2727 (correct), ack 2950613896 win 23 10:48:55.102963 IP (tos 0x0, ttl 49, id 16399, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > NATBOX.http: P 0:120(120) ack 1 win 23 10:48:58.103078 IP (tos 0x0, ttl 49, id 16401, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > NATBOX.http: P 0:120(120) ack 1 win 23 10:48:58.366344 IP (tos 0x0, ttl 49, id 16403, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x26af (correct), ack 1 win 23 10:49:04.103204 IP (tos 0x0, ttl 49, id 16405, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > NATBOX.http: P 0:120(120) ack 1 win 23 10:49:04.363943 IP (tos 0x0, ttl 49, id 16407, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x26af (correct), ack 1 win 23 10:49:16.101583 IP (tos 0x0, ttl 49, id 16409, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > NATBOX.http: P 0:120(120) ack 1 win 23 10:49:16.363475 IP (tos 0x0, ttl 49, id 16411, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x26af (correct), ack 1 win 23 10:49:40.100796 IP (tos 0x0, ttl 49, id 16413, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > NATBOX.http: P 0:120(120) ack 1 win 23 10:49:40.563898 IP (tos 0x0, ttl 49, id 16415, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x26af (correct), ack 1 win 23 10:50:28.099396 IP (tos 0x0, ttl 49, id 16417, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > NATBOX.http: P 0:120(120) ack 1 win 23 10:50:28.761678 IP (tos 0x0, ttl 49, id 16419, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x26af (correct), ack 1 win 23 10:52:04.093668 IP (tos 0x0, ttl 49, id 16421, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > NATBOX.http: P 0:120(120) ack 1 win 23 10:52:04.093678 IP (tos 0x0, ttl 48, id 16421, offset 0, flags [DF], proto: TCP (6), length: 160) CLIENT.61736 > WEBSERVER.http: P 1589600741:1589600861(120) ack 2950613896 win 23 10:52:04.291021 IP (tos 0x0, ttl 49, id 16423, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x25d3 (correct), ack 217 win 27 10:52:04.291028 IP (tos 0x0, ttl 48, id 16423, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > WEBSERVER.http: ., cksum 0x7b91 (correct), ack 217 win 27 10:52:04.300708 IP (tos 0x0, ttl 49, id 16425, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x253c (correct), ack 368 win 27 10:52:04.300714 IP (tos 0x0, ttl 48, id 16425, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > WEBSERVER.http: ., cksum 0x7afa (correct), ack 368 win 27 10:52:04.301417 IP (tos 0x0, ttl 49, id 16427, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: F, cksum 0x253b (correct), 120:120(0) ack 368 win 27 10:52:04.301438 IP (tos 0x0, ttl 48, id 16427, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > WEBSERVER.http: F, cksum 0x7af9 (correct), 120:120(0) ack 368 win 27 10:52:04.498875 IP (tos 0x0, ttl 49, id 16429, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > NATBOX.http: ., cksum 0x253a (correct), ack 369 win 27 10:52:04.498881 IP (tos 0x0, ttl 48, id 16429, offset 0, flags [DF], proto: TCP (6), length: 40) CLIENT.61736 > WEBSERVER.http: ., cksum 0x7af8 (correct), ack 369 win 27

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• QoS - split bandwidth across all IPs during high load

  - by Matthew Iselin

  We have a Linux-based router which is currently working fairly well, but our network only has a 1.5 mbps incoming connection. The network is small, but during high load periods some systems can end up dominating the bandwidth. For example, a client downloading a file can easily saturate the connection leaving everyone else with barely any access to the outside world. Naturally, I'd like to fix this. I believe a combination of iptables rules and tc is in order, but I have no idea how to go about distributing the bandwidth evenly across the clients. It would be nice if there was a way to divide the bandwidth only across clients that are actually utilising the connection as well, rather than hard limit each connection to (bandwidth / number of clients).

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• Server Configuration / Important Parameter for 500Req/Second

  - by Sparsh Gupta

  I am configuring a server to be used as nginx server for a very heavy traffic website. It is expected to receive traffic from a large number of IP addresses simultaneously. It is expected to get 500Req/Second with atleast 20Million unique IPs connecting it. One of the problems I noticed in my previos server was related to iptables / ipconntrack. I am not aware of this behaviour and would be glad to know which all parameters of a ubuntu / debian (32/64) bit machine should I tweek to get maximum performance from the server. I can put in a lot of RAM on the server but mission critical task is the response times. We ideally dont want any connection to be hanging / timing out / waiting and want as low as possible overall response times. P.S. We are also looking for a kick ass freelancer system admin who can help us figuring / setting this all up. Reach me incase you have some spare time and interested in working on some very heavy traffic website servers.

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• TIME_WAIT connections not being cleaned up after timeout period expires

  - by Mark Dawson

  I am stress testing one of my servers by hitting it with a constant stream of new network connections, the tcp_fin_timeout is set to 60, so if I send a constant stream of something like 100 requests per second, I would expect to see a rolling average of 6000 (60 * 100) connections in a TIME_WAIT state, this is happening, but looking in netstat (using -o) to see the timers, I see connections like: TIME_WAIT timewait (0.00/0/0) where their timeout has expired but the connection is still hanging around, I then eventually run out of connections. Anyone know why these connections don't get cleaned up? If I stop creating new connections they do eventually disappear but while I am constantly creating new connections they don't, seems like the kernel isn't getting chance to clean them up? Is there some other config options I need to set to remove the connections as soon as they have expired? The server is running Ubuntu and my web server is nginx. Also it has iptables with connection tracking, not sure if that would cause these TIME_WAIT connections to live on. Thanks Mark.

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• How to add authentication to ssh dynamic port forwarding?

  - by Aalex Gabi

  I am using ssh as a SOCKS server by running this command on the server: ssh -f2qTnND *:1080 root@localhost There is one problem: anybody can connect to the server and use it's internet connection. Options: To use iptables to filter access to the server, but I connect to the server from various non-statically allocated IP addresses so I would have to edit very frequently those filters which can be annoying. To install a SOCKS server on the remote. Ultimately this is the last option if there is no other simpler way to do it. (I am very lazy) Launching the same command on clients machines. The problem here is that some clients don't run on Linux and it is awkward to set up the tunnel (Windows + Putty). Is there a way to add authentication to a SOCKS server made using ssh? Bonus question: How to add encryption between the client and the server (made using ssh)?

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• Pure-FTPd linux upload problems - 500 Unknown command

  - by user1801273

  I'm running Centos with Kloxo CP and PureFTPd on VPS based on HyperVM. The problem - during the day, there are periods when FTP wors fine for hours, but sometimes it dies with "500 Unknown command" code. for files larger than 2Kb. This is really weird - with files less than 2472-2484 bytes everything would work fine, but with bigger files ftp would start writing file, would drop on 2Kb and would return "500 Unknown command" . This happens on Passive AND/OR Active connections for any filetypes. Logs are showing like the file was uploaded successfully , but the speed nearby the action would be 0.3 -0.5 Kb , when normal operation would report 70-150Kb/s speeds. I do have some Iptables firewalls on both HyperVM host,and VPS , however these are static, and most of the time it works just fine. Any suggestions on where to look for a solution would be appreciated :)

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• Route packets from one VPN to another

  - by Mike

  I have two OpenVPN servers (10.8.0.0 and 10.9.0.0) set up on my OpenSUSE server. Within one network, each computer is visible to any other one, but I'd like to make it so that computers are visible across networks. I'd like to route the packets like this: when a user (say 10.8.0.6) pings an address on the other VPN (10.9.0.6), the packets are routed to the 10.9.0.1 and then to the appropriate computer in this VPN. How do I achieve this using iptables or a different tool? I tried the commands at the end of this section with no avail.

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• TCP Zero Window with no corresponding Window Update

  - by Gandalf

  I am trying to debug a network issue and am using Wireshark and tcpdump to grab packets from my server. I have one client application that is grabbing all my available connections and then holding them, trying to send A LOT of data and essentially causing an unintentional DOS attack. While debugging I notice that I see my server sending "Window Closed" and "Zero Window" TCP packets - but never sending any "Window Update" packets. I am guessing this is why the client never lets go of the connections (it still has more data to send and is waiting). Has anyone ever seen this type of behavior before? Let's not get into the reasons why I haven't set up an iptables rule to limit concurrent connections (yeah I know). I also recently changed the MTU from 1500 to 9000 - could this have such a negative effect? (Linux) Thanks.

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• forward ssh ports on EC2

  - by Will Glass

  I have an SSH server on a private subnet within an EC2 vpc listening for ssh on port 9022 I also have a nat instance (standard Amazon EC2 nat) on a public instance. I would like to forward incoming SSH connections (port 9022) to my nat to the internal server (port 9022). I tried this, but it didn't work: sudo iptables -t nat -I PREROUTING -p tcp -i eth0 --dport 9022 -j DNAT --to-destination 10.0.2.11:9022 I verified that 10.0.2.11 is listening on port 9022. (I can telnet). I verified my security group allows incoming port 9022. I verified that /proc/sys/net/ipv4/ip_forward is 1. What am I missing? Edit: Turns out this was correct after all. I had a mistake in my security group.

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