We have a real server behind the proxy server (or a firewall). The client must connect to the real server through IPSec Transport mode Encryption. The IPSec Transport mode works between the two hosts and fails whenever a hop is introduced between the two hosts. This is due to Checksum Integrity failure at the destination which is due to DNAT at the intermittent hop between 2 hosts.
We want something to encapsulate the ESP Transport mode packet either in an IP Header or UDP encapsulation or something like this ->
A --------------------> GATEWAY --------------------> B
Transport (Transport mode is received Packet
and IP header is accepted
encapsulated on the packet
and is forwarded again)
Is something like this possible where the Client sends the Transport mode ESP packet and the intermittent hosts encapsulate that packet (either in IP/UDP) and then send it to the destination?
Is there any RFC for these types of scenarios?
Related
I am sending packets to a Windows network card (eth1) using the Linux sendto() function and a RAW socket (socket(AF_INET, SOCK_RAW, IPPROTO_RAW);). However, although the packets are addressed to the IP address of the network card, the host OS appears to "ignore" the packets.
For example, the network card has IP 192.168.1.2, and my userspace application sends a network packet containing a ping addressed to 192.168.1.2. I can observe in Wireshark the ping arrive on the network device at 192.168.1.2, however no reply is generated. The TTL on the ping is non-zero, so I'm lost as to why the host OS would appear to "ignore" packets destined for it.
Equivalently, if I create a UDP socket and bind it listening to 192.168.1.2 on port 5050, and then send a userspace UDP packet addressed to 192.168.1.2 on port 5050, the packet is never delivered to the port.
What would cause a packet to be ignored by the network card that receives it?
Is there any socket flag needed if I'm sending packets in from userspace (over a custom IP tunnel) to force processing of the packets, as if they came from a router?
The issue turned out to be the native windows firewall, disabling the firewall fixed this issue.
In addition, if republishing network packets on a network device, if a single device (mac addr) is publishing multiple ip packets from various source ips, windows may filter out packets with the assumption that mac<->ip is a unique 1:1 mapping.
My friend told me that TCP doesn't need port forward.
What exactly he said is if the server is port forwarded the client can request something and the server will respond without port forward.
And I agreed with that even though I'm not sure it is true.
Later he said it is the same with UDP which I do not believe.
MAINLY THE QUESTION IS
If a client requests something on a server with TCP, does it need to be port forwarded to receive the response?
Also is it the same for UDP?
If the request from the client is a SYN for connect call then only a SYN-ACK response will be allowed through NAT. If the NAT supports simultaneous open connection then a SYN response from server will also be allowed through NAT. After the connection is established then client and server can communicate freely without any restriction. Port forwarding is not needed.
For UDP after a packet from client to server is sent then anything from server can be received through exact same public port of the NAT from which the first packet was sent. No port forwarding needed.
Which software libraries does exist for such task for Linux, Windows OS?
Does it exist some info in RFC how people should do it?
I'm interesting how can I create functionality for my C++ project like presented here in that software: https://secure.logmein.com/ru/products/hamachi/download.aspx
There is not much difference if you want to make a connection through TURN relay server. The only difference is how TCP and UDP creates connection and nothing else.
There are some big differences if you want to make P2P connection.
If you are in same network(behind same NAT): In UDP you send a stun binding request to your peer candidate and then if you get a response back then you know you are connected. Same in TCP you have to create one active socket on one side and one passive socket on another. And then send syn from active socket and receive it from passive socket and then send syn ack to the active socket. And then active socket send an ack and the connection is established.
If you are in different Network(behind different NAT): You have to employ TCP hole punching technique for making a connection. Because your NAT won't allow a TCP syn packet through if previously no packet was sent to the address the syn is coming from.
TCP hole punching in details:
You have to use a TCP simultaneous open socket. This socket acts in both active and passive mode. Both end needs to know each others private and public IP:Port.
TCP simultaneous open will happen as follows:
Peer A keeps sending SYN to Peer B
Peer B keeps sending SYN to Peer A
When NAT-a receives the outgoing SYN from Peer A, it creates a mapping in its state machine.
When NAT-b receives the outgoing SYN from Peer B, it creates a mapping in its state machine.
Both SYN cross somewhere along the network path, then:
SYN from Peer A reaches NAT-b, SYN from Peer B reaches NAT-a
Depending on the timing of these events (where in the network the SYN cross),
at least one of the NAT will let the incoming SYN through, and map it to the internal destination peer
Upon receipt of the SYN, the peer sends a SYN+ACK back and the connection is established.
From WIKI.
Also to learn about TCP simultaneous open connection read from here. To learn about NAT filtering behavior see this answer.
I am looking at traffic generated by my computer when socks server is defined.
I read over the internet and see that its possible to route udp also trough the proxy server.
when i try using different apps that uses UDP and allows socks settings, it uses it only for tcp traffic. why?
I have defined SOCKS5, as i understand that v4 doesnt support udp (why?)
i tried an example, Vuze client - its expert mode allows to prefer udp traffic, setup socks server and even at this point, any udp goes directly to peers.
My wish is to monitor the traffic and see how its transmitted, is it over UDP connection with socks server, or does it actually connects to the socks server in TCP and sends the data, which is then sent via udp to the destination?
When a client wants to relay UDP traffic over the SOCKS5 proxy, the client makes a UDP associate request over the TCP. SOCKS5 server then returns an available UDP port to the client to send UDP packages to.
Client then starts sending the UDP packages that needs to be relayed to the new UDP port that is available on SOCKS5 server. SOCKS5 server redirects these UDP packages to the remote server and redirects the UDP packages coming from the remote server back to the client.
When client wants to terminate the connection, it sends a FIN package over the TCP. The SOCKS5 server then terminates the UDP connection created for the client and then terminates the TCP connection.
Double SSH Tunnel Manager support SOCKS5 With UDP
3proxy Server support UDP
So right now I'm using only TCP for my clients - they connect to the server, open socket and freely getting packets.
But what if I will decide to use also UDP in my game? Will they gonna have to open ports? For example, if they are using a regular WiFi, can I send UDP to the client without having opening ports problem?
Thanks.
TCP and UDP are just two examples of transport layer implementations. Both of them are using term 'port' to determine which app should receive incoming packet, but they could be routed/filtered differently by routers/switches/firewalls/etc.
So the answer is no. You will have similar problems with opening ports. Just except 'TCP port xxx should be opened' you have to demand 'UDP port xxx should be opened'.
In most home networks firewall rules allow outgoing packets (requests) to any remote port (on your server for example, where this port should be opened). And when such a packet goes through a router - it creates temporary rule to allow answers come back to the local port from which request packet.
So, normal scenario is like that:
Packet originated from home computer with IP 5.5.5.5. Lets say it has source UDP port 55555, source IP address 5.5.5.5 and destination port 8888.
Packet reaches home router. As it is going from inside - router allows it to pass through and creates rule say for 2 minutes to allow packets targeted to 5.5.5.5 to UDP port 55555.
Packet reaches corporate router before your server. It has rule to pass packets for port 8888 so packet is allowed to go.
Your server receives the packet and processes it. In response it creates packet for IP 5.5.5.5 and UDP port 55555.
Corporate router allows response to go.
Home router allows response to go according to temporary rule.
Your computer receives the response.
Corporate computers and routers often more restrictive to ensure security, so second point could restrict packet if your user (IP 5.5.5.5) is in corporate network.
It is very simplified as in reality there's almost always things like NAT and rules are more complex... But in general it gives the idea how it works internally.