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  • Books for Computer Networking

    - by Altimet Gaandu
    Hi, I am a student of computer engineering from Vasula University, Somalia. We have a subject called Advanced Computer Networks and the following is the list of recommended books: Text Books: 1. B. A. Forouzan, "TCP/IP Protocol Suite", Tata McGraw Hill edition, Third Edition. 2. N. Olifer, V. Olifer, "Computer Networks: Principles, Technologies and Protocols for Network design", Wiley India Edition, First edition. References: 1. W.Richard Stevens, "TCP/IP Volume1, 2, 3", Addison Wesley. 2. D.E.Comer,"TCP/IPVolumeI and II", PearsonEducation. . 3.W.R. Stevens, "Unix Network Programming", Vol. 1, Pearson Education. 4. J.Walrand, P. Var~fya, "High Performance Communication Networks", Morgan Kaufmann. . 5. A.S.Tanenbaum,"Computer Networks", Pearson Education, Fourth Edition. But we have been unable to find these either in the market or on the internet (read: torrents). Please provide download links to any of these books and oblige. Thanks.

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  • c++ networking issue- retrnsmittion without ccongestion

    - by gln
    I wrote an application in c++ which send data over tcp connection to several machines.as part of the protocol I use in my application, the other side sends hearbeat messages from time to time, then I know that the connection is still alive. now, I want this application to work on 100 machines or more at the same time. but, I see that sometimes I don't get these heartbeat messages although they sent: I see in wireshark that the packet arrived, then my OS doesn't ack on this message, so there are some retransmit without any ack from my OS. if I look in the window size property - I saw that there is no issue in this part. what can be the root cause for this behavior? it is something in my code that I should change? this is my select code: int res = select(fdCount, &readFds, NULL, NULL, NULL ); I'm using server 2008 r2. Please help me! thanks

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  • Dovecot starting and running, but not listening on any port

    - by Dženis Macanovic
    Among others things I'm in charge of a Debian GNU/Linux (Wheezy) DomU for the mail services of the company i work for. Yesterday one HDD that was used for this particular server has died. After installing Debian again, Dovecot decided to no longer listen on any ports (checked with netstat -l). Other services (like Postfix and MySQL) work without problems. dovecot -n: # 2.1.7: /etc/dovecot/dovecot.conf # OS: Linux 3.2.0-3-amd64 x86_64 Debian wheezy/sid ext3 auth_mechanisms = plain login disable_plaintext_auth = no first_valid_uid = 150 last_valid_uid = 150 mail_gid = mail mail_location = maildir:/var/vmail/%d/%n mail_uid = vmail namespace inbox { inbox = yes location = prefix = } pass db { args = /etc/dovecot/dovecot-sql.conf.ext driver = sql } plugin { sieve = ~/.dovecot.sieve sieve_dir = ~/sieve } service auth { unix_listener /var/spool/postfix/private/auth { group = postfix mode = 0660 user = postfix } unix_listener auth-userdb { group = mail mode = 0666 user = vmail } } service imap-login { inet_listener imaps { port = 993 ssl = yes } } service pop3-login { inet_listener pop3s { port = 995 ssl = yes } } ssl_cert = </etc/ssl/private/mail.crt ssl_key = </etc/ssl/private/mail.key userdb { args = /etc/dovecot/dovecot-sql.conf.ext driver = sql } protocol imap { mail_max_userip_connections = 25 } UID 150 is vmail (I double checked file permissions). I didn't install Dovecot from source, but via apt from the official Debian US mirror. There are no messages concerning Dovecot in /var/log/syslog except for: Oct 21 06:36:29 server dovecot: master: Dovecot v2.1.7 starting up (core dumps disabled) Any ideas?

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  • networking application and GUI in python

    - by pygabriel
    I'm writing an application that sends files over network, I want to develop a custom protocol to not limit myself in term on feature richness (http wouldn't be appropriate, the nearest thing is the bittorrent protocol maybe). I've tried with twisted, I've built a good app but there's a bug that makes my GUI blocking, so I've to switch to another framework/strategy. What do you suggest? Using raw sockets and using gtk mainloop (there are select-like functions in the toolkit) is too much difficult? It's viable running two mainloops in different threads? Asking for suggestions

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  • RTL8188CE doesn't connect to any wifi access points

    - by Drakmail
    I'm using network manager to connect. Also, tryed iwconfig. Results are same. I even try to connect to open access point — results are same. More information: Drakmail@thinkpad-x220:~$ lspci | grep Network | grep -v Ethernet 03:00.0 Network controller: Realtek Semiconductor Co., Ltd. RTL8188CE 802.11b/g/n WiFi Adapter (rev 01) Drakmail@thinkpad-x220:~$ uname -a Linux thinkpad-x220 3.1.0 #1 SMP PREEMPT Wed Oct 26 02:19:49 UTC 2011 x86_64 Intel(R) Core(TM) i5-2410M CPU @ 2.30GHz GenuineIntel GNU/Linux Drakmail@thinkpad-x220:~$ dmesg | tail -n 10 [ 846.901574] rtl8192c_common: Loading firmware file rtlwifi/rtl8192cfw.bin [ 906.812461] rtl8192c_common: Loading firmware file rtlwifi/rtl8192cfw.bin [ 966.728810] rtl8192c_common: Loading firmware file rtlwifi/rtl8192cfw.bin [ 1026.639676] rtl8192c_common: Loading firmware file rtlwifi/rtl8192cfw.bin [ 1030.925574] rtl8192c_common: Loading firmware file rtlwifi/rtl8192cfw.bin At this moment I try to connect to open wifi ap: [ 1031.252403] wlan0: direct probe to 00:24:8c:55:fa:ed (try 1/3) [ 1031.451943] wlan0: direct probe to 00:24:8c:55:fa:ed (try 2/3) [ 1031.651658] wlan0: direct probe to 00:24:8c:55:fa:ed (try 3/3) [ 1031.851354] wlan0: direct probe to 00:24:8c:55:fa:ed timed out [ 1086.544960] rtl8192c_common: Loading firmware file rtlwifi/rtl8192cfw.bin My distribution: Drakmail@thinkpad-x220:~$ cat /etc/*version AgiliaLinux release 8.0.0 (Sammy) (Something between Slackware and Archlinux). Also, I saw that wifi module to often trying to load a firmware file. Any ideas what it would be?

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  • Networking Icon Keeps Disappearing

    - by Zelda64fan
    Almost every time I unlock my computer the networking icon and the Bluetooth icons are missing from the panel. They also disappear if I disable networking with the 'hardware switch', even though before they would just switch to a 'disabled' look. I know I can get the networking one back by running nm-applet, but I'd rather just find a way to make it stop disappearing. What causes this? This is on 12.10 64-bit, if it matters. UPDATE: I ran it from terminal, and got this: $ nm-applet ** Message: applet now removed from the notification area ** Message: PID 31340 (we are 28924) sent signal 15, shutting down... And then it exited. So it thinks it's supposed to quit...? I haven't been able to figure out what process had that ID.

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  • Video streaming over multi display units

    - by ramdaz
    We have to share video across around 4/8 terminals at a public facility where we need to display live video from within the facility, as well as display messages(advertisements), and also play videos(not live) which need to be controlled centrally from another location. We can do central location handling over Internet, over ssh. What we want to do is connect cameras to a computer, and use the computer to display over multiple display units. We need to do live titling if possible. Once the live local telecast which usually takes about an hour or two a day, we would like to play other videos locally off the PC server. Preferably everything should run off Linux, since budgets are very constrained.... Addendum -- Its not over WAN, it's over a local area. I prefer not using LAN, we would rather use co-axial cable if possible. The reason is if it's LAN, I need some kind of an Networking device, at least a thin client

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  • enable tcp_syncookies even after reboot

    - by Tim
    I'm running Scientific Linux 6.1 and would like to set net.ipv4.tcp_syncookies=1. I've set that in /etc/sysctl.conf and, if I do a sysctl -p then sysctl -q net.ipv4.tcp_syncookies it shows it's properly set. Sadly, if I reboot the machine, and sysctl -q again, it goes back to 0. I've tried to grep around and see if something else is resetting it to 0 during the boot process but haven't turned up anything. I've googled and everything points to sysctl.conf. The only thing I can think of is maybe networking isn't up by the time that file gets read but, honestly, I'm a developer and well beyond my natural skills here:) I'm tempted to just set it directly in /etc/init.d/network but then that feels hackish and so, I thought better of it and I'm here in search of the "right" way to do it. Any pointers?

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  • Media Disconnected Networking Issue

    - by Chris
    After rearranging my physical network in my apartment my Windows Vista machine can no longer connect to the network. I have tested all of the cabling by connecting other devices and everything is fine. I'm able to connect using other computers, I've even tested a brand new ethernet adapter and the network status still reads "media disconnected". I have no idea where to go from here. My setup is as follows: Cable modem - router - hardwired ethernet cable to computer.

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  • Linux boot on a raid1 software raid ?

    - by azera
    Hello I am trying to convert my single disk boot to a raid1 boot So far here is what i have: I sucessfully create the raid 1 as degraded with the new drive alone, I copied all the data on it I can mount that raid 1, see its files etc I already have a raid5 that is working on the same box (although not booting on it) I have installed grub on both drive When grub boot, it loads the kernel alright, but during the kernel boot it fails to load the "root block device" The kernel tells me : 1 - detected that root device is an md device 2 - determining root devices 3 - mounting root 4 - mounting /dev/md125 on /newroot failed: input/output error. Please enter another root device: ... At this point, if I enter /dev/sda3 (my "old" root device that isn't converted to raid yet) everything boots fine without the root. The /dev/md125 device is indeed created but it seems to be created after the error happens, as in it creates it after loading the device, when mdadm is loaded. Somehow it looks like it can't/doesn't load the raid array before it needs to mount it, and I don't know how I can solve that. My config files (taken from the system once it boots with sda3 as root device): $ cat /etc/mdadm.conf ARRAY /dev/md/md0-r5 metadata=0.90 UUID=1a118934:c831bdb3:64188b84:66721085 ARRAY /dev/md125 metadata=0.90 UUID=48ec4190:a80d4dde:64188b84:66721085 $ cat /proc/mdstat Personalities : [raid1] [raid6] [raid5] [raid4] [raid0] [raid10] md125 : active raid1 sdc3[1] 477853312 blocks [2/1] [_U] md127 : active raid5 sdd[0] sdf[3] sdb[2] sde[1] 4395415488 blocks level 5, 64k chunk, algorithm 2 [4/4] [UUUU] unused devices: <none> $ cat /boot/grub/menu.lst default 0 timeout 8 splashimage=(hd0,0)/boot/grub/splash.xpm.gz title Gentoo Linux 2.6.31-r10 root (hd0,0) #kernel /boot/kernel-genkernel-x86_64-2.6.31-gentoo-r10 root=/dev/ram0 real_root=/dev/sda3 kernel /boot/kernel-genkernel-x86_64-2.6.31-gentoo-r10 root=/dev/md125 md=125,/dev/sdc3,/dev/sda3 initrd /boot/initramfs-genkernel-x86_64-2.6.31-gentoo-r10 # blkid /dev/sda1: UUID="89fee223-b845-4e0a-8a0b-e6cf695d5bcf" TYPE="ext2" /dev/sda2: UUID="a72296a8-d7d4-447f-a34b-ee920fd1a767" TYPE="swap" /dev/sda3: UUID="97eb0a6a-c385-4a9d-bf74-c0bab1fa4dc1" TYPE="ext3" /dev/sdb: UUID="1a118934-c831-bdb3-6418-8b8466721085" TYPE="linux_raid_member" /dev/sdc1: UUID="d36537fd-19a0-b8a3-6418-8b8466721085" TYPE="linux_raid_member" /dev/sdd: UUID="1a118934-c831-bdb3-6418-8b8466721085" TYPE="linux_raid_member" /dev/sde: UUID="1a118934-c831-bdb3-6418-8b8466721085" TYPE="linux_raid_member" /dev/md127: UUID="13a41589-4cf1-4c04-91ca-37484182c783" TYPE="ext4" /dev/sdf: UUID="1a118934-c831-bdb3-6418-8b8466721085" TYPE="linux_raid_member" /dev/sdc2: UUID="a1916397-1b48-45d7-9f98-73aa521e882f" TYPE="swap" /dev/sdc3: UUID="48ec4190-a80d-4dde-6418-8b8466721085" TYPE="linux_raid_member" /dev/md125: UUID="c947ed64-1d4d-4d1d-b4d2-24669fff916e" SEC_TYPE="ext2" TYPE="ext3" # mdadm -E mdadm: No devices to examine # fdisk -l Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0xe975e9fc Device Boot Start End Blocks Id System /dev/sda1 1 5 40131 83 Linux /dev/sda2 6 1311 10490445 82 Linux swap / Solaris /dev/sda3 1312 60801 477853425 83 Linux Disk /dev/sdc: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0xe975e9fc Device Boot Start End Blocks Id System /dev/sdc1 1 5 40131 83 Linux /dev/sdc2 6 1311 10490445 82 Linux swap / Solaris /dev/sdc3 1312 60801 477853425 83 Linux Disk /dev/md125: 489.3 GB, 489321791488 bytes 2 heads, 4 sectors/track, 119463328 cylinders Units = cylinders of 8 * 512 = 4096 bytes Disk identifier: 0x00000000 Disk /dev/md125 doesn't contain a valid partition table

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  • Forwarding RDP via a Linux machine using iptables: Not working

    - by Nimmy Lebby
    I have a Linux machine and a Windows machine behind a router that implements NAT (the diagram might be overkill, but was fun to make): I am forwarding RDP port (3389) on the router to the Linux machine because I want to audit RDP connections. For the Linux machine to forward RDP traffic, I wrote these iptables rules: iptables -t nat -A PREROUTING -p tcp --dport 3389 -j DNAT --to-destination win-box iptables -A FORWARD -p tcp --dport 3389 -j ACCEPT The port is listening on the Windows machine: C:\Users\nimmy>netstat -a Active Connections Proto Local Address Foreign Address State (..snip..) TCP 0.0.0.0:3389 WIN-BOX:0 LISTENING (..snip..) And the port is forwarding on the Linux machine: # tcpdump port 3389 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 01:33:11.451663 IP shieldsup.grc.com.56387 > linux-box.myapt.lan.ms-wbt-server: Flags [S], seq 94663035, win 8192, options [mss 1460], length 0 01:33:11.451846 IP shieldsup.grc.com.56387 > win-box.myapt.lan.ms-wbt-server: Flags [S], seq 94663035, win 8192, options [mss 1460], length 0 However, I am not getting any successful RDP connections from the outside. The port is not even responding: C:\Users\outside-nimmy>telnet example.com 3389 Connecting To example.com...Could not open connection to the host, on port 3389: Connect failed Any ideas? Update Per @Zhiqiang Ma, I looked at nf_conntrack proc file during a connection attempt and this is what I see (192.168.3.1 = linux-box, 192.168.3.5 = win-box): # cat /proc/net/nf_conntrack | grep 3389 ipv4 2 tcp 6 118 SYN_SENT src=4.79.142.206 dst=192.168.3.1 sport=43142 dport=3389 packets=6 bytes=264 [UNREPLIED] src=192.168.3.5 dst=4.79.142.206 sport=3389 dport=43142 packets=0 bytes=0 mark=0 secmark=0 zone=0 use=2 2nd update Got tcpdump on the router and it seems that win-box is sending an RST packet: 21:20:24.767792 IP shieldsup.grc.com.45349 > linux-box.myapt.lan.3389: S 19088743:19088743(0) win 8192 <mss 1460> 21:20:24.768038 IP shieldsup.grc.com.45349 > win-box.myapt.lan.3389: S 19088743:19088743(0) win 8192 <mss 1460> 21:20:24.770674 IP win-box.myapt.lan.3389 > shieldsup.grc.com.45349: R 721745706:721745706(0) ack 755785049 win 0 Why would Windows be doing this?

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  • Visualization Tools for Networks that Change with Time

    - by devin
    Does anyone known of any good Linux tools for visualizing networks that change (quickly) with time. I'm interested in things like: Routes between nodes Delays between nodes (especially as they change with time) Throughput I have root access to all the nodes (so I can run daemons on them all). Also, assume that I either have a management network that is stable or I will collect data and then analyze it offline.

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  • How to detect VPN disconnection with vpnc?

    - by Abhinav
    What is the easiest way to detect that a vpnc connection on Linux/Ubuntu has disconnected? Manually, I think the way to detect is to check whether the interface (tun0) appears in /sbin/ifconfig output. Is there a better way to find out immediately, so that a script can be run to restart the connection?

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  • Kernel Log "TCP: Treason uncloaked!"

    - by hurikhan77
    On one linux server (Gentoo hardened), we are experiencing bursts of the following messages in dmesg from time to time: TCP: Treason uncloaked! Peer xx.xx.xxx.xxx:65039/80 shrinks window 4094157295:4094160199. Repaired. Is there anything we should take care of or is this normal? Update: Maybe related, we are using net.ipv4.tcp_congestion_control = cubic. Kernel version is 2.6.28 with Gentoo hardening patches.

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  • Disable dhcp client over one interface

    - by Lopoc
    Hi to all I'm encountering a problem on a sever with two ethernet interfaces(etho and eth1), it runs linux-ubuntu-server. I need eth1 not make any dhcp request, becouse I need it to be only a listening interface, obviusly I need eth0 running normally. So how can i disable any dhcpclient ation over eth1? thank in advance.

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  • Latency in TCP/IP-over-Ethernet networks

    - by aix
    What resources (books, Web pages etc) exist out there that: explain the causes of latency in TCP/IP-over-Ethernet networks; mention tools for looking out for things that cause latency (e.g. certain entries in netstat -s); suggest ways to tweak the Linux TCP stack to reduce TCP latency (Nagle, socket buffers etc). The closest I am aware of is this document, but it's rather brief. Alternatively, you're welcome to answer the above questions directly.

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  • Keep source IP after NAT

    - by John Miller
    Until today I used a cheapy router so I can share my internet connection and keep a webserver online too, while using NAT. Users IP ($_SERVER['REMOTE_ADDR']) was fine, I was seeing class A IPs of users. But as traffic grown up everyday, I had to install a Linux Server (Debian) to share my Internet Connection, because my old router couldn't keep the traffic anymore. I shared the internet via IPTABLES using NAT, but now, after forwarding port 80 to my webserver, now instead of seeing real users IP, I see my Gateway IP (Linux Internal IP) as any user IP Address. How to solve this issue? I edited my post, so I can paste the rules I'm currently using. #!/bin/sh #I made a script to set the rules #I flush everything here. iptables --flush iptables --table nat --flush iptables --delete-chain iptables --table nat --delete-chain iptables -F iptables -X # I drop everything as a general rule, but this is disabled under testing # iptables -P INPUT DROP # iptables -P OUTPUT DROP # these are the loopback rules iptables -A INPUT -i lo -j ACCEPT iptables -A OUTPUT -o lo -j ACCEPT # here I set the SSH port rules, so I can connect to my server iptables -A INPUT -p tcp --sport 513:65535 --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT iptables -A OUTPUT -p tcp --sport 22 --dport 513:65535 -m state --state ESTABLISHED -j ACCEPT # These are the forwards for 80 port iptables -t nat -A PREROUTING -p tcp -s 0/0 -d xx.xx.xx.xx --dport 80 -j DNAT --to 192.168.42.3:80 iptables -t nat -A POSTROUTING -o eth0 -d xx.xx.xx.xx -j SNAT --to-source 192.168.42.3 iptables -A FORWARD -p tcp -s 192.168.42.3 --sport 80 -j ACCEPT # These are the forwards for bind/dns iptables -t nat -A PREROUTING -p udp -s 0/0 -d xx.xx.xx.xx --dport 53 -j DNAT --to 192.168.42.3:53 iptables -t nat -A POSTROUTING -o eth0 -d xx.xx.xx.xx -j SNAT --to-source 192.168.42.3 iptables -A FORWARD -p udp -s 192.168.42.3 --sport 53 -j ACCEPT # And these are the rules so I can share my internet connection iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE iptables -A FORWARD -i eth0:1 -j ACCEPT If I delete the MASQUERADE part, I see my real IP while echoing it with PHP, but I don't have internet. How to do, to have internet and see my real IP while ports are forwarded too? ** xx.xx.xx.xx - is my public IP. I hid it for security reasons.

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  • TCP: Treason uncloaked!

    - by hurikhan77
    On one linux server (Gentoo hardened), we are experiencing bursts of the following messages in dmesg from time to time: TCP: Treason uncloaked! Peer xx.xx.xxx.xxx:65039/80 shrinks window 4094157295:4094160199. Repaired. Is there anything we should take care of or is this normal?

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  • clear IP address of Ethernet interface

    - by jackhab
    What is the Linux command to clear IP address of an interface without bringing it down and/or restarting network services. Seems strange ifconfig is able to change IP address but has no option to clear it, or am I wrong? EDIT:As simple as ifconfig eth0 0.0.0.0. They should have put it in the man

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  • Discovering proxy servers on a private network

    - by AIB
    Suppose that I am in a private network of computers (say each having ip addresses 192.168.. ). Some of the machines( we have no information regarding their ip, name and no physical access to the servers) in the network are connected to internet and they run an http proxy at some port say 3128. Is there a program which can be run on Windows or Linux which will give me the list of machines(ip addresses and ports if possible) acting as proxy servers?

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  • Testifying rasing net.core.somaxconn can make a difference

    - by petermolnar
    I got into an argument on the net.core.somaxconn parameter: I was told that it will not make any difference if we change the default 128. I believed this might be enough proof: "If the backlog argument is greater than the value in /proc/sys/net/core/somaxconn, then it is silently truncated to that value" http://linux.die.net/man/2/listen but it's not. Does anyone know a method to testify this with two machines, sitting on a Gbit network? The best would be against MySQL, LVS, apache2 ( 2.2 ), memcached.

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  • bridge traffic limiting via tc

    - by jackhab
    I have a Linux machine running as a bridge simulating various network conditions. I use tc for this. Introducing delays or packet loss is quite simple but I got into trouble trying to configure bandwidth limiting. Can you, please, show me how to limit all the traffic going through my bridge without any special rules and condition, simply limit it to 1Mb/s? Thanks. PS Your favorite link to tc tutorial will be appreciated.

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