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  • Why we need to read() before write() in TCP server program?

    - by Naga
    Hi, As per my understanding a simple TCP server will be coded as follows. socket() - bind() - listen() - accept() - read() - write() The clients will be written as follows. socket() - bind()(Optional) - connect() - write() - read() Please note the order difference in read() and write() calls between client and server program. Is it a requirement to always read() before write() in a server program and if, then why? Thanks, Naga

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  • SQL SERVER – Mirroring Configured Without Domain – The server network address TCP://SQLServerName:50

    - by pinaldave
    Regular readers of my blog will be aware of my friend who called me few days ago with very a funny SQL Problem SQL SERVER – SSMS Query Command(s) completed successfully without ANY Results. This time, it did not take long before he called me up with another interesting problem, although the issue he was facing this time was not that interesting and also very specific to him, however, he insisted me to share with all of you. Let us understand his situation at first. My friend is preparing for DBA exam Exam 70-450: PRO: Designing, Optimizing and Maintaining a Database Server Infrastructure using Microsoft SQL Server 2008 and for the same, he was trying to set up replication on his local laptop. He had installed two different instances of SQL Server on his computer and every time when he started the mirroring, it failed with common error message. The server network address “TCP://SQLServer:5023? cannot be reached or does not exist. Check the network address name and that the ports for the local and remote endpoints are operational. (Microsoft SQL Server, Error: 1418) Well, before he contacted me, he searched online and checked my article written on the error in mirroring. However, he tried all the four suggestions, but it did not solve his problem. He called me at a reasonable time of late evening (unlike last time, which was midnight!). I even tried all the seven different suggestions myself, as previously proposed in my article; however, none of them worked. While looking at closely at services, I noticed something very simple. He was running all the instances on ‘Network Services’. In fact, his computer was a stand-alone computer. There was no network at all. Also, there was no domain or any other advance network concepts implemented. I just changed services from ‘Network Services’ to ‘Local System’ as his SQL Server was running on his local system and there were no network services. This prompted to restart the services. As this was not the production server and his development machine, we restarted the services on the laptop (do not restart services on production server without proper planning). After changing the ‘services log on’ account to localsystem, when he attempted to reconfigure the mirroring it worked right away. As usually in production server, proper domains are configured and advance network concepts are implemented I had never faced this type of problem earlier. My friend insisted to post this solution to his situation, wherein there was no domain configured and setting up mirroring was throwing an error. According to him, this is bound to help people, like him, who are preparing for certification using single system. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Error Messages, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: SQL Certifications, SQL Mirroring

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  • Different versions of iperf for windows give totally different results

    - by Albert Mata
    Measuring TCP output from a Windows client to Solaris server: WXP SP3 with iperf 1.7.0 -- returns an average around 90Mbit Same client, same server but iperf 2.0.5 for windows -- returns an average of 8.5 Mbit Similar discrepancies have been observed connecting to other servers (W2008, W2003) It's difficult to get to some conclusions when different versions of the same tool provide vastly different results. Example below: C:\tempiperf -v (from iperf.fr) iperf version 2.0.5 (08 Jul 2010) pthreads C:\tempiperf -c solaris10 Client connecting to solaris10, TCP port 5001 TCP window size: 64.0 KByte (default) [ 3] local 10.172.181.159 port 2124 connected with 10.172.180.209 port 5001 [ ID] Interval Transfer Bandwidth [ 3] 0.0-10.2 sec 10.6 MBytes 8.74 Mbits/sec Abysmal perfomance, but now I test from the same host (Windows XP SP3 32bit and 100Mbit) to the same server (Solaris 10/sparc 64bit and 1Gbit running iperf 2.0.5 with default window of 48k) with the old iperf C:\temp1iperf -v iperf version 1.7.0 (13 Mar 2003) win32 threads C:\temp1iperf.exe -c solaris10 -w64k Client connecting to solaris10, TCP port 5001 TCP window size: 64.0 KByte [1208] local 10.172.181.159 port 2128 connected with 10.172.180.209 port 5001 [ ID] Interval Transfer Bandwidth [1208] 0.0-10.0 sec 112 MBytes 94.0 Mbits/sec So one iperf with a 64k window says 8.75Mbit and the old iperf with the same window size says 94.0Mbit. These results are constant through repeated tests. From my testing launching iperf(old) with window size "x" and iperf(new) with window size "x" instead of producing the same or very close results produce totally different results. The only difference I see is the old compiled as win32 threads vs. pthreads but parallelism (-P 10) appears to work in both. Anyone has a clue or can recommend a tool that gives results I can trust?? EDIT: Looking at traces from (old) iperf it sets the TCP Window Scale flag to 3 in the SYN packet, when I run the (new) iperf this is set to 0 in the initial packet. A quick analysis of the window size through the exchange shows the (old) iperf moving back and forth but mostly at 32k while the (new) iperf mostly keeps at 64k. Maybe it will help somebody to connect the dots.

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  • Cisco PIX 515 doesn't seem to be passing traffic through according to static route

    - by Liquidkristal
    Ok, so I am having a spot of bother with a Cisco PIX515, I have posted the current running config below, now I am no cisco expert by any means although I can do basic stuff with them, now I am having trouble with traffic sent from the outside to address: 10.75.32.25 it just doesn't appear to be going anywhere. Now this firewall is deep inside a private network, with an upstream firewall that we don't manage. I have spoken to the people that look after that firewall and they say they they have traffic routing to 10.75.32.21 and 10.75.32.25 and thats it (although there is a website that runs from the server 172.16.102.5 which (if my understanding is correct) gets traffic via 10.75.32.23. Any ideas would be greatly appreciated as to me it should all just work, but its not (obviously if the config is all correct then there could be a problem with the web server that we are trying to access on 10.75.32.25, although the users say that they can get to it internally (172.16.102.8) which is even more confusing) PIX Version 6.3(3) interface ethernet0 auto interface ethernet1 auto interface ethernet2 auto nameif ethernet0 outside security0 nameif ethernet1 inside security100 nameif ethernet2 academic security50 fixup protocol dns maximum-length 512 fixup protocol ftp 21 fixup protocol h323 h225 1720 fixup protocol h323 ras 1718-1719 fixup protocol http 80 fixup protocol rsh 514 fixup protocol rtsp 554 fixup protocol sip 5060 fixup protocol sip udp 5060 fixup protocol skinny 2000 fixup protocol smtp 25 fixup protocol sqlnet 1521 fixup protocol tftp 69 names name 195.157.180.168 outsideNET name 195.157.180.170 globalNAT name 195.157.180.174 gateway name 195.157.180.173 Mail-Global name 172.30.31.240 Mail-Local name 10.75.32.20 outsideIF name 82.219.210.17 frogman1 name 212.69.230.79 frogman2 name 78.105.118.9 frogman3 name 172.16.0.0 acadNET name 172.16.100.254 acadIF access-list acl_outside permit icmp any any echo-reply access-list acl_outside permit icmp any any unreachable access-list acl_outside permit icmp any any time-exceeded access-list acl_outside permit tcp any host 10.75.32.22 eq smtp access-list acl_outside permit tcp any host 10.75.32.22 eq 8383 access-list acl_outside permit tcp any host 10.75.32.22 eq 8385 access-list acl_outside permit tcp any host 10.75.32.22 eq 8484 access-list acl_outside permit tcp any host 10.75.32.22 eq 8485 access-list acl_outside permit ip any host 10.75.32.30 access-list acl_outside permit tcp any host 10.75.32.25 eq https access-list acl_outside permit tcp any host 10.75.32.25 eq www access-list acl_outside permit tcp any host 10.75.32.23 eq www access-list acl_outside permit tcp any host 10.75.32.23 eq https access-list acl_outside permit tcp host frogman1 host 10.75.32.23 eq ssh access-list acl_outside permit tcp host frogman2 host 10.75.32.23 eq ssh access-list acl_outside permit tcp host frogman3 host 10.75.32.23 eq ssh access-list acl_outside permit tcp any host 10.75.32.23 eq 2001 access-list acl_outside permit tcp host frogman1 host 10.75.32.24 eq 8441 access-list acl_outside permit tcp host frogman2 host 10.75.32.24 eq 8441 access-list acl_outside permit tcp host frogman3 host 10.75.32.24 eq 8441 access-list acl_outside permit tcp host frogman1 host 10.75.32.24 eq 8442 access-list acl_outside permit tcp host frogman2 host 10.75.32.24 eq 8442 access-list acl_outside permit tcp host frogman3 host 10.75.32.24 eq 8442 access-list acl_outside permit tcp host frogman1 host 10.75.32.24 eq 8443 access-list acl_outside permit tcp host frogman2 host 10.75.32.24 eq 8443 access-list acl_outside permit tcp host frogman3 host 10.75.32.24 eq 8443 access-list acl_outside permit tcp any host 10.75.32.23 eq smtp access-list acl_outside permit tcp any host 10.75.32.23 eq ssh access-list acl_outside permit tcp any host 10.75.32.24 eq ssh access-list acl_acad permit icmp any any echo-reply access-list acl_acad permit icmp any any unreachable access-list acl_acad permit icmp any any time-exceeded access-list acl_acad permit tcp any 10.0.0.0 255.0.0.0 eq www access-list acl_acad deny tcp any any eq www access-list acl_acad permit tcp any 10.0.0.0 255.0.0.0 eq https access-list acl_acad permit tcp any 10.0.0.0 255.0.0.0 eq 8080 access-list acl_acad permit tcp host 172.16.102.5 host 10.64.1.115 eq smtp pager lines 24 logging console debugging mtu outside 1500 mtu inside 1500 mtu academic 1500 ip address outside outsideIF 255.255.252.0 no ip address inside ip address academic acadIF 255.255.0.0 ip audit info action alarm ip audit attack action alarm pdm history enable arp timeout 14400 global (outside) 1 10.75.32.21 nat (academic) 1 acadNET 255.255.0.0 0 0 static (academic,outside) 10.75.32.22 Mail-Local netmask 255.255.255.255 0 0 static (academic,outside) 10.75.32.30 172.30.30.36 netmask 255.255.255.255 0 0 static (academic,outside) 10.75.32.23 172.16.102.5 netmask 255.255.255.255 0 0 static (academic,outside) 10.75.32.24 172.16.102.6 netmask 255.255.255.255 0 0 static (academic,outside) 10.75.32.25 172.16.102.8 netmask 255.255.255.255 0 0 access-group acl_outside in interface outside access-group acl_acad in interface academic route outside 0.0.0.0 0.0.0.0 10.75.32.1 1 timeout xlate 3:00:00 timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 rpc 0:10:00 h225 1:00:00 timeout h323 0:05:00 mgcp 0:05:00 sip 0:30:00 sip_media 0:02:00 timeout uauth 0:05:00 absolute aaa-server TACACS+ protocol tacacs+ aaa-server RADIUS protocol radius aaa-server LOCAL protocol local snmp-server host outside 172.31.10.153 snmp-server host outside 172.31.10.154 snmp-server host outside 172.31.10.155 no snmp-server location no snmp-server contact snmp-server community CPQ_HHS no snmp-server enable traps floodguard enable telnet 172.30.31.0 255.255.255.0 academic telnet timeout 5 ssh timeout 5 console timeout 0 terminal width 120 Cryptochecksum:hi2u : end PIX515#

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  • Computer Networks UNISA - Chap 10 &ndash; In Depth TCP/IP Networking

    - by MarkPearl
    After reading this section you should be able to Understand methods of network design unique to TCP/IP networks, including subnetting, CIDR, and address translation Explain the differences between public and private TCP/IP networks Describe protocols used between mail clients and mail servers, including SMTP, POP3, and IMAP4 Employ multiple TCP/IP utilities for network discovery and troubleshooting Designing TCP/IP-Based Networks The following sections explain how network and host information in an IPv4 address can be manipulated to subdivide networks into smaller segments. Subnetting Subnetting separates a network into multiple logically defined segments, or subnets. Networks are commonly subnetted according to geographic locations, departmental boundaries, or technology types. A network administrator might separate traffic to accomplish the following… Enhance security Improve performance Simplify troubleshooting The challenges of Classful Addressing in IPv4 (No subnetting) The simplest type of IPv4 is known as classful addressing (which was the Class A, Class B & Class C network addresses). Classful addressing has the following limitations. Restriction in the number of usable IPv4 addresses (class C would be limited to 254 addresses) Difficult to separate traffic from various parts of a network Because of the above reasons, subnetting was introduced. IPv4 Subnet Masks Subnetting depends on the use of subnet masks to identify how a network is subdivided. A subnet mask indicates where network information is located in an IPv4 address. The 1 in a subnet mask indicates that corresponding bits in the IPv4 address contain network information (likewise 0 indicates the opposite) Each network class is associated with a default subnet mask… Class A = 255.0.0.0 Class B = 255.255.0.0 Class C = 255.255.255.0 An example of calculating  the network ID for a particular device with a subnet mask is shown below.. IP Address = 199.34.89.127 Subnet Mask = 255.255.255.0 Resultant Network ID = 199.34.89.0 IPv4 Subnetting Techniques Subnetting breaks the rules of classful IPv4 addressing. Read page 490 for a detailed explanation Calculating IPv4 Subnets Read page 491 – 494 for an explanation Important… Subnetting only applies to the devices internal to your network. Everything external looks at the class of the IP address instead of the subnet network ID. This way, traffic directed to your network externally still knows where to go, and once it has entered your internal network it can then be prioritized and segmented. CIDR (classless Interdomain Routing) CIDR is also known as classless routing or supernetting. In CIDR conventional network class distinctions do not exist, a subnet boundary can move to the left, therefore generating more usable IP addresses on your network. A subnet created by moving the subnet boundary to the left is known as a supernet. With CIDR also came new shorthand for denoting the position of subnet boundaries known as CIDR notation or slash notation. CIDR notation takes the form of the network ID followed by a forward slash (/) followed by the number of bits that are used for the extended network prefix. To take advantage of classless routing, your networks routers must be able to interpret IP addresses that don;t adhere to conventional network class parameters. Routers that rely on older routing protocols (i.e. RIP) are not capable of interpreting classless IP addresses. Internet Gateways Gateways are a combination of software and hardware that enable two different network segments to exchange data. A gateway facilitates communication between different networks or subnets. Because on device cannot send data directly to a device on another subnet, a gateway must intercede and hand off the information. Every device on a TCP/IP based network has a default gateway (a gateway that first interprets its outbound requests to other subnets, and then interprets its inbound requests from other subnets). The internet contains a vast number of routers and gateways. If each gateway had to track addressing information for every other gateway on the Internet, it would be overtaxed. Instead, each handles only a relatively small amount of addressing information, which it uses to forward data to another gateway that knows more about the data’s destination. The gateways that make up the internet backbone are called core gateways. Address Translation An organizations default gateway can also be used to “hide” the organizations internal IP addresses and keep them from being recognized on a public network. A public network is one that any user may access with little or no restrictions. On private networks, hiding IP addresses allows network managers more flexibility in assigning addresses. Clients behind a gateway may use any IP addressing scheme, regardless of whether it is recognized as legitimate by the Internet authorities but as soon as those devices need to go on the internet, they must have legitimate IP addresses to exchange data. When a clients transmission reaches the default gateway, the gateway opens the IP datagram and replaces the client’s private IP address with an Internet recognized IP address. This process is known as NAT (Network Address Translation). TCP/IP Mail Services All Internet mail services rely on the same principles of mail delivery, storage, and pickup, though they may use different types of software to accomplish these functions. Email servers and clients communicate through special TCP/IP application layer protocols. These protocols, all of which operate on a variety of operating systems are discussed below… SMTP (Simple Mail transfer Protocol) The protocol responsible for moving messages from one mail server to another over TCP/IP based networks. SMTP belongs to the application layer of the ODI model and relies on TCP as its transport protocol. Operates from port 25 on the SMTP server Simple sub-protocol, incapable of doing anything more than transporting mail or holding it in a queue MIME (Multipurpose Internet Mail Extensions) The standard message format specified by SMTP allows for lines that contain no more than 1000 ascii characters meaning if you relied solely on SMTP you would have very short messages and nothing like pictures included in an email. MIME us a standard for encoding and interpreting binary files, images, video, and non-ascii character sets within an email message. MIME identifies each element of a mail message according to content type. MIME does not replace SMTP but works in conjunction with it. Most modern email clients and servers support MIME POP (Post Office Protocol) POP is an application layer protocol used to retrieve messages from a mail server POP3 relies on TCP and operates over port 110 With POP3 mail is delivered and stored on a mail server until it is downloaded by a user Disadvantage of POP3 is that it typically does not allow users to save their messages on the server because of this IMAP is sometimes used IMAP (Internet Message Access Protocol) IMAP is a retrieval protocol that was developed as a more sophisticated alternative to POP3 The single biggest advantage IMAP4 has over POP3 is that users can store messages on the mail server, rather than having to continually download them Users can retrieve all or only a portion of any mail message Users can review their messages and delete them while the messages remain on the server Users can create sophisticated methods of organizing messages on the server Users can share a mailbox in a central location Disadvantages of IMAP are typically related to the fact that it requires more storage space on the server. Additional TCP/IP Utilities Nearly all TCP/IP utilities can be accessed from the command prompt on any type of server or client running TCP/IP. The syntaxt may differ depending on the OS of the client. Below is a list of additional TCP/IP utilities – research their use on your own! Ipconfig (Windows) & Ifconfig (Linux) Netstat Nbtstat Hostname, Host & Nslookup Dig (Linux) Whois (Linux) Traceroute (Tracert) Mtr (my traceroute) Route

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  • C# TCP Hole Punch (NAT Traversal) Library or something?

    - by user293531
    I want to do TCP Hole Punching (NAT Traversal) in C#. It can be done with a rendevouzs server if needed. I found http://sharpstunt.codeplex.com/ but can not get this to work. Ideally i need some method which i give a PortNumber (int) as parameter that after a call to this method is available ("Port Forwarded") at the NAT. It would be also ok if the methode just returns some port number which is then available at the NAT. Has anybody done this in C# ? Can you give me working examples for sharpstunt or something else? Thank you

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  • How can I connect to Android with ADB over TCP?

    - by martinjd
    I am attempting to debug an application on a Motorola Droid but I am having some difficulty connecting to the device via USB. My development server is a Windows 7 64bit VM running in HyperV and so I cannot connect directly via USB in the guest or from the host. I installed a couple of different USB over TCP solutions but the connection appears to have issues since the adb monitor reports "devicemonitor failed to start monitoring" repeatedly. I was wondering if there is a way to connect directly from the client on the development machine to the daemon on the device using the network instead of the usb connection or possibly other viable options?

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  • When binding a client TCP socket to a specific local port with Winsock, SO_REUSEADDR does not have a

    - by Checkers
    I'm binding a client TCP socket to a specific local port. To handle the situation where the socket remains in TIME_WAIT state for some time, I use setsockopt() with SO_REUSEADDR on a socket. It works on Linux, but does not work on Windows, I get WSAEADDRINUSE on connect() call when the previous connection is still in TIME_WAIT. MSDN is not exactly clear what should happen with client sockets: [...] For server applications that need to bind multiple sockets to the same port number, consider using setsockopt (SO_REUSEADDR). Client applications usually need not call bind at all—connect chooses an unused port automatically. [...] How do I avoid this?

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  • What happens with TCP packets between two Socket.BeginReceive calls?

    - by Rodrigo
    I have a doubt about socket programming. I am developing a TCP packet sniffer. I am using Socket.BeginAccept, Socket.BeginReceive to capture every packet, but when a packet is received I have to process something. It is a fast operation, but would take some milliseconds, and then call BeginReceive again. My question is, what would happen if some packets are sent while I am processing, and haven't called BeginReceive? Are packets lost, or are they buffered internally? Is there a limit?

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  • What alternative is there to writing a TCP/IP data relay?

    - by LoudNPossiblyRight
    I am about to write a tcp/ip data relay - application that passes a one way stream of data from one host/port to another host/port. Initially it will be generic, but later on i will customize it to the need of a specific business request. I am guessing that something generic already exists out there so my question is: Has anyone used a third party (preferably open source) data relay in a production environment, if so what is, and do you recommend it? Any platform is fine. Thanks.

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  • What structure of data use to communicate via tcp/ip in java?

    - by rmaster
    Let's assume I want to send many messages between 2 programs made in java that use TCP sockets. I think the most convienient way is to send objects like: PrintStream ps = new PrintStream(s.getOutputStream()); ObjectOutputStream oos = new ObjectOutputStream(ps); some_kind_of_object_here; oos.writeObject(some_kind_of_object_here); ps.print(oos); I want to send, strings, numbers, HashMaps, boolean values How can I do this using fx 1 object that can store all that properties? I though about ArrayList that is serializable and we can put there everything but is not elegant way. I want to send different types of data because user can choose from a variety of options that server can do for it. Any advices?

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  • Why is UDP + a software reliable ordering system faster than TCP?

    - by Ricket
    Some games today use a network system that transmits messages over UDP, and ensures that the messages are reliable and ordered. For example, RakNet is a popular game network engine. It uses only UDP for its connections, and has a whole system to ensure that packets can be reliable and ordered if you so choose. My basic question is, what's up with that? Isn't TCP the same thing as ordered, reliable UDP? What makes it so much slower that people have to basically reinvent the wheel?

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  • Library like ENet, but for TCP?

    - by Milo
    I'm not looking to use boost::asio, it is overly complex for my needs. I'm building a game that is cross platform, for desktop, iPhone and Android. I found a library called ENet which is pretty much what I need, but it uses UDP which does not seem to support encryption and a few other things. Given that the game is an event driven card game, TCP seems like the right fit. However, all I have found is WINSOCK / berkley sockets and bost::asio. Here is a sample client server application with ENet: #include <enet/enet.h> #include <stdlib.h> #include <string> #include <iostream> class Host { ENetAddress address; ENetHost * server; ENetHost* client; ENetEvent event; public: Host() :server(NULL) { enet_initialize(); setupServer(); } void setupServer() { if(server) { enet_host_destroy(server); server = NULL; } address.host = ENET_HOST_ANY; /* Bind the server to port 1234. */ address.port = 1721; server = enet_host_create (& address /* the address to bind the server host to */, 32 /* allow up to 32 clients and/or outgoing connections */, 2 /* allow up to 2 channels to be used, 0 and 1 */, 0 /* assume any amount of incoming bandwidth */, 0 /* assume any amount of outgoing bandwidth */); } void daLoop() { while(true) { /* Wait up to 1000 milliseconds for an event. */ while (enet_host_service (server, & event, 5000) > 0) { ENetPacket * packet; switch (event.type) { case ENET_EVENT_TYPE_CONNECT: printf ("A new client connected from %x:%u.\n", event.peer -> address.host, event.peer -> address.port); /* Store any relevant client information here. */ event.peer -> data = "Client information"; /* Create a reliable packet of size 7 containing "packet\0" */ packet = enet_packet_create ("packet", strlen ("packet") + 1, ENET_PACKET_FLAG_RELIABLE); /* Extend the packet so and append the string "foo", so it now */ /* contains "packetfoo\0" */ enet_packet_resize (packet, strlen ("packetfoo") + 1); strcpy ((char*)& packet -> data [strlen ("packet")], "foo"); /* Send the packet to the peer over channel id 0. */ /* One could also broadcast the packet by */ /* enet_host_broadcast (host, 0, packet); */ enet_peer_send (event.peer, 0, packet); /* One could just use enet_host_service() instead. */ enet_host_flush (server); break; case ENET_EVENT_TYPE_RECEIVE: printf ("A packet of length %u containing %s was received from %s on channel %u.\n", event.packet -> dataLength, event.packet -> data, event.peer -> data, event.channelID); /* Clean up the packet now that we're done using it. */ enet_packet_destroy (event.packet); break; case ENET_EVENT_TYPE_DISCONNECT: printf ("%s disconected.\n", event.peer -> data); /* Reset the peer's client information. */ event.peer -> data = NULL; } } } } ~Host() { if(server) { enet_host_destroy(server); server = NULL; } atexit (enet_deinitialize); } }; class Client { ENetAddress address; ENetEvent event; ENetPeer *peer; ENetHost* client; public: Client() :peer(NULL) { enet_initialize(); setupPeer(); } void setupPeer() { client = enet_host_create (NULL /* create a client host */, 1 /* only allow 1 outgoing connection */, 2 /* allow up 2 channels to be used, 0 and 1 */, 57600 / 8 /* 56K modem with 56 Kbps downstream bandwidth */, 14400 / 8 /* 56K modem with 14 Kbps upstream bandwidth */); if (client == NULL) { fprintf (stderr, "An error occurred while trying to create an ENet client host.\n"); exit (EXIT_FAILURE); } /* Connect to some.server.net:1234. */ enet_address_set_host (& address, "192.168.2.13"); address.port = 1721; /* Initiate the connection, allocating the two channels 0 and 1. */ peer = enet_host_connect (client, & address, 2, 0); if (peer == NULL) { fprintf (stderr, "No available peers for initiating an ENet connection.\n"); exit (EXIT_FAILURE); } /* Wait up to 5 seconds for the connection attempt to succeed. */ if (enet_host_service (client, & event, 20000) > 0 && event.type == ENET_EVENT_TYPE_CONNECT) { std::cout << "Connection to some.server.net:1234 succeeded." << std::endl; } else { /* Either the 5 seconds are up or a disconnect event was */ /* received. Reset the peer in the event the 5 seconds */ /* had run out without any significant event. */ enet_peer_reset (peer); puts ("Connection to some.server.net:1234 failed."); } } void daLoop() { ENetPacket* packet; /* Create a reliable packet of size 7 containing "packet\0" */ packet = enet_packet_create ("backet", strlen ("backet") + 1, ENET_PACKET_FLAG_RELIABLE); /* Extend the packet so and append the string "foo", so it now */ /* contains "packetfoo\0" */ enet_packet_resize (packet, strlen ("backetfoo") + 1); strcpy ((char*)& packet -> data [strlen ("backet")], "foo"); /* Send the packet to the peer over channel id 0. */ /* One could also broadcast the packet by */ /* enet_host_broadcast (host, 0, packet); */ enet_peer_send (event.peer, 0, packet); /* One could just use enet_host_service() instead. */ enet_host_flush (client); while(true) { /* Wait up to 1000 milliseconds for an event. */ while (enet_host_service (client, & event, 1000) > 0) { ENetPacket * packet; switch (event.type) { case ENET_EVENT_TYPE_RECEIVE: printf ("A packet of length %u containing %s was received from %s on channel %u.\n", event.packet -> dataLength, event.packet -> data, event.peer -> data, event.channelID); /* Clean up the packet now that we're done using it. */ enet_packet_destroy (event.packet); break; } } } } ~Client() { atexit (enet_deinitialize); } }; int main() { std::string a; std::cin >> a; if(a == "host") { Host host; host.daLoop(); } else { Client c; c.daLoop(); } return 0; } I looked at some socket tutorials and they seemed a bit too low level. I just need something that abstracts away the platform (eg, no WINSOCKS) and that has basic ability to keep track of connected clients and send them messages. Thanks

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  • Millions of SYN_RECV connections, no DDoS

    - by ThomK
    We have such server structure: reverse proxy (nginx) - worker (uwsgi) - postgresql / memcached. All servers are in local network behind router, with NATed external ip:ports (http/s 80/443 to proxy, and ssh 22 to all servers). Problem is, that sometimes proxy server netstat reports MILLIONS of SYN_RECV connections. From same IP / same ports. Like that: nginx ~ # netstat -n | grep 83.238.153.195 tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV tcp 0 0 192.168.1.1:80 83.238.153.195:3107 SYN_RECV [...] And this is not DDoS, because all IPs affected belongs to our website users. On side note, users says that it's not affecting them. Website is online and working, but... that particular one (from example above) told me that website is down and Firefox can't connect. I've done tcpdump. 19:42:14.826011 IP 83.238.153.195.zephyr-srv > 192.168.1.1.http: Flags [S], seq 1845850583, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:14.826042 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:17.887331 IP 83.238.153.195.zephyr-srv > 192.168.1.1.http: Flags [S], seq 1845850583, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:17.887343 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:19.065497 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:23.918064 IP 83.238.153.195.zephyr-srv > 192.168.1.1.http: Flags [S], seq 1845850583, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:23.918076 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:25.265499 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:37.265501 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:37.758051 IP 83.238.153.195.2107 > 192.168.1.1.http: Flags [S], seq 564208067, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:37.758069 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:40.714360 IP 83.238.153.195.2107 > 192.168.1.1.http: Flags [S], seq 564208067, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:40.714374 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:41.665503 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:46.751073 IP 83.238.153.195.2107 > 192.168.1.1.http: Flags [S], seq 564208067, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:42:46.751087 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:47.665498 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:42:59.865499 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:01.265500 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:13.320382 IP 83.238.153.195.2114 > 192.168.1.1.http: Flags [S], seq 2136055006, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:13.320399 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:16.320556 IP 83.238.153.195.2114 > 192.168.1.1.http: Flags [S], seq 2136055006, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:16.320569 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:17.665498 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:22.250069 IP 83.238.153.195.2114 > 192.168.1.1.http: Flags [S], seq 2136055006, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:22.250080 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:23.665500 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:23.865501 IP 192.168.1.1.http > 83.238.153.195.2107: Flags [S.], seq 3188568660, ack 564208068, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:35.665498 IP 192.168.1.1.http > 83.238.153.195.2114: Flags [S.], seq 3754336171, ack 2136055007, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:37.903038 IP 83.238.153.195.2213 > 192.168.1.1.http: Flags [S], seq 2918118729, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:37.903054 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:40.772899 IP 83.238.153.195.2213 > 192.168.1.1.http: Flags [S], seq 2918118729, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:40.772912 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:41.865500 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:46.793057 IP 83.238.153.195.2213 > 192.168.1.1.http: Flags [S], seq 2918118729, win 65535, options [mss 1412,nop,wscale 0,nop,nop,sackOK], length 0 19:43:46.793069 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:47.865500 IP 192.168.1.1.http > 83.238.153.195.2213: Flags [S.], seq 4145523337, ack 2918118730, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 19:43:49.465503 IP 192.168.1.1.http > 83.238.153.195.zephyr-srv: Flags [S.], seq 2835837547, ack 1845850584, win 5840, options [mss 1460,nop,nop,sackOK,nop,wscale 7], length 0 Anyone have some thoughts on that?

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