# FreeRTOS TCP 4.0.0 Port Binding Problem **URL:** \ **Category:** Libraries\ **Created:** [August 18, 2023, 9:19am UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010 "2023-08-18T09:19:12Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![ozanagma](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/ozanagma/32/3136_2.png) [@ozanagma](https://forums.freertos.org/u/ozanagma)\ **Post date:** [August 18, 2023, 9:19am UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/1 "2023-08-18T09:19:12Z")
Hi, Yesterday I downloaded [FreeRTOS 4.0.0](https://github.com/FreeRTOS/FreeRTOS-Plus-TCP/tree/V4.0.0). I do my tests on Zynq. I initialized one interface and two endpoints. I try to send periodic message from both endpoints but I am getting an error from the bind function because I use the same port number for both endpoints. The reason is that FreeRTOS TCP 4.0.0 has only one **xBoundUDPSocketsList**. Is it normal for multi ethernet interface? Have a good work. ---
**Author:** ![RAc](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/rac/32/1389_2.png) [@RAc](https://forums.freertos.org/u/RAc)\ **Post date:** [August 18, 2023, 10:24am UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/2 "2023-08-18T10:24:04Z")
Are you implying that this is a new behavior in 4.0.0, behaving differently from previous versions? If not, I would argue that this is expected behavior as two distinct endpoints on the same target would need different port/IP address combos to allow the TCP stack to direct incoming packets to a distinct endpoint. ---
**Author:** ![ozanagma](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/ozanagma/32/3136_2.png) [@ozanagma](https://forums.freertos.org/u/ozanagma)\ **Post date:** [August 18, 2023, 10:36am UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/3 "2023-08-18T10:36:06Z")
Hi RAc, I have two distinct endpoints. 192.168.1.100 is the IP address of first one. 192.168.1.101 is the other one. I created two sockets . First socket is created from 192.168.1.100 adress and 17000 port. Second socket is created form 192.168.1.101 adress and 17000 port. But second socket’s bind function gives an error. The word **Socket** is the combination of port and IP address. So the first combo(192.168.1.100/17000) is different than the second(192.1.68.1.101/1700) one. For that reason it shouldn’t give error. Is there something I’m thinking wrong? ---
**Author:** ![tony-josi-aws](https://avatars.discourse-cdn.com/v4/letter/t/a6a055/32.png) [@tony-josi-aws](https://forums.freertos.org/u/tony-josi-aws)\ **Post date:** [August 18, 2023, 11:37am UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/4 "2023-08-18T11:37:07Z")
Hi @ozanagma, Thanks for checking out v4.0.0 of FreeRTOS+TCP and posting your feedback. As you have already figured, the entire range of port numbers is shared between all the available endpoints/interfaces; there are no endpoint/interface specific socket-port binding lists for either TCP or UDP. Is there a specific use case that requires you to use the same port numbers? ---
**Author:** ![RAc](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/rac/32/1389_2.png) [@RAc](https://forums.freertos.org/u/RAc)\ **Post date:** [August 18, 2023, 11:37am UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/5 "2023-08-18T11:37:33Z")
No, we are perfectly in sync, you just didn’t state explicitly that you bind to distinct IP addresses. However, is it intended that both IP addresses are in the same subnet? Again, did it work without error in previous releases? ---
**Author:** ![ozanagma](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/ozanagma/32/3136_2.png) [@ozanagma](https://forums.freertos.org/u/ozanagma)\ **Post date:** [August 18, 2023, 11:54am UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/6 "2023-08-18T11:54:27Z")
Sorry for the missing information. I want it to work on the same subnet. I don’t know because this is the first version of TCP 4.0.0. that I have used. ---
**Author:** ![ozanagma](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/ozanagma/32/3136_2.png) [@ozanagma](https://forums.freertos.org/u/ozanagma)\ **Post date:** [August 18, 2023, 12:06pm UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/7 "2023-08-18T12:06:07Z")
Hi @tony-josi-aws I was using multiple cards to be able to test a library that uses Ethernet. These cards were using TCP 3.1. I found out that there is multi ethernet in TCP 4.0.0. I thought if I put the eth physical into loopback mode it could do it on a single board. For this reason, I copied the code on the second card to the first without changing it and I got the error I mentioned above. It’s definitely not a must-have feature, but that’s how the problem came to me. ---
**Author:** ![RAc](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/rac/32/1389_2.png) [@RAc](https://forums.freertos.org/u/RAc)\ **Post date:** [August 18, 2023, 12:53pm UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/8 "2023-08-18T12:53:06Z")
Can you share the code that sets up the sockets? ---
**Author:** ![rtel](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/rtel/32/31_2.png) [@rtel](https://forums.freertos.org/u/rtel)\ **Post date:** [August 18, 2023, 1:18pm UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/9 "2023-08-18T13:18:44Z")
Perhaps there should be a list of port numbers per subnet, but you may find routing of packets within FreeRTOS+TCP wouldn’t work as intended if you used the same port number on the same subnet for two endpoints. Separately - Having the same server, on a known port number, on two interfaces at once would be a reason to allow the same port number on more than one interface. For example, having an HTTP server on 10.10.10.10:80 and 1.2.3.4:80 at the same time. ---
**Author:** ![ozanagma](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/ozanagma/32/3136_2.png) [@ozanagma](https://forums.freertos.org/u/ozanagma)\ **Post date:** [August 18, 2023, 1:29pm UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/10 "2023-08-18T13:29:44Z")
> [@RAc](#): > > Can you share the code that sets up the soc Of course. ```auto static uint32_t interface_count = 0; Socket = FreeRTOS_socket(FREERTOS_AF_INET, FREERTOS_SOCK_DGRAM, FREERTOS_IPPROTO_UDP); if(FREERTOS_INVALID_SOCKET == Socket){ ... } freertos_sockaddr addr; addr.sin_family = FREERTOS_AF_INET; addr.sin_address.ulIP_IPv4 = FreeRTOS_inet_addr(p_local_ip); addr.sin_port = FreeRTOS_htons(LOCAL_UDP_PORT + interface_count); BaseType_t ret = FreeRTOS_bind(Socket, &addr, sizeof(addr)); if(0 != ret){ ... } interface_count++; ``` This is the constructor of class. I added the static **interface\_count** variable because of binding error. ---
**Author:** ![RAc](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/rac/32/1389_2.png) [@RAc](https://forums.freertos.org/u/RAc)\ **Post date:** [August 18, 2023, 1:41pm UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/11 "2023-08-18T13:41:00Z")
And you are sure that the IP addresses passed to the two constructors are distinct? Just to rule out the obvious fallacies that we all fall victim to every once in a while… ---
**Author:** ![ozanagma](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/ozanagma/32/3136_2.png) [@ozanagma](https://forums.freertos.org/u/ozanagma)\ **Post date:** [August 18, 2023, 2:30pm UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/12 "2023-08-18T14:30:57Z")
You are right. Such mistakes happen a lot. This is the constans. ```auto const char GATEWAY_IP[] = "192.168.1.1"; const char NET_MASK[] = "255.255.255.0"; const char CARD_0_IP[] = "192.168.1.100"; const uint32_t CARD_0_COMMUNICATION_PORT = 6000; const uint32_t CARD_0_DISCOVERY_PORT = 6001; #define CARD_0_MAC_ADDR0 0x00 #define CARD_0_MAC_ADDR1 0x11 #define CARD_0_MAC_ADDR2 0x22 #define CARD_0_MAC_ADDR3 0x33 #define CARD_0_MAC_ADDR4 0x44 #define CARD_0_MAC_ADDR5 0x55 const char CARD_IP_1[] = "192.168.1.110"; const uint32_t CARD_1_COMMUNICATION_PORT = 6010; const uint32_t CARD_1_DISCOVERY_PORT = 6011; #define CARD_1_MAC_ADDR0 0x00 #define CARD_1_MAC_ADDR1 0x11 #define CARD_1_MAC_ADDR2 0x22 #define CARD_1_MAC_ADDR3 0x33 #define CARD_1_MAC_ADDR4 0x44 #define CARD_1_MAC_ADDR5 0x55 ``` And this is the initialization part. ```auto const uint32_t card_0_ip_addr = FreeRTOS_inet_addr(CARD_0_IP); const uint8_t card_0_ip_arr[4] = {(uint8_t)((card_0_ip_addr >> 0) & 0xFF), (uint8_t)((card_0_ip_addr >> 8) & 0xFF), (uint8_t)((card_0_ip_addr >> 16) & 0xFF), (uint8_t)((card_0_ip_addr >> 24) & 0xFF)}; const uint8_t card_0_mac_arr[6] = { CARD_0_MAC_ADDR0, CARD_0_MAC_ADDR1, CARD_0_MAC_ADDR2, CARD_0_MAC_ADDR3, CARD_0_MAC_ADDR4, CARD_0_MAC_ADDR5 }; const uint32_t card_1_ip_addr = FreeRTOS_inet_addr(CARD_IP_1); const uint8_t card_1_ip_arr[4] = {(uint8_t)((card_1_ip_addr >> 0) & 0xFF), (uint8_t)((card_1_ip_addr >> 8) & 0xFF), (uint8_t)((card_1_ip_addr >> 16) & 0xFF), (uint8_t)((card_1_ip_addr >> 24) & 0xFF)}; const uint8_t card_1_mac_arr[6] = { CARD_1_MAC_ADDR0, CARD_1_MAC_ADDR1, CARD_1_MAC_ADDR2, CARD_1_MAC_ADDR3, CARD_1_MAC_ADDR4, CARD_1_MAC_ADDR5 }; const uint32_t gateway_addr = FreeRTOS_inet_addr(GATEWAY_IP); const uint32_t netmask_addr = FreeRTOS_inet_addr(NET_MASK); const uint8_t gateway_arr[4] = {(uint8_t)((gateway_addr >> 0) & 0xFF), (uint8_t)((gateway_addr >> 8) & 0xFF), (uint8_t)((gateway_addr >> 16) & 0xFF), (uint8_t)((gateway_addr >> 24) & 0xFF)}; const uint8_t net_mask_arr[4] = {(uint8_t)((netmask_addr >> 0) & 0xFF), (uint8_t)((netmask_addr >> 8) & 0xFF), (uint8_t)((netmask_addr >> 16) & 0xFF), (uint8_t)((netmask_addr >> 24) & 0xFF)}; static NetworkInterface_t xInterfaces[1]; static NetworkEndPoint_t xEndPoints[2]; pxZynq_FillInterfaceDescriptor(0, &(xInterfaces[0])); FreeRTOS_FillEndPoint(&(xInterfaces[0]), &(xEndPoints[0]), card_0_ip_arr, net_mask_arr, gateway_arr, gateway_arr, card_0_mac_arr); FreeRTOS_FillEndPoint(&(xInterfaces[0]), &(xEndPoints[1]), card_1_ip_arr, net_mask_arr, gateway_arr, gateway_arr, card_1_mac_arr); FreeRTOS_IPInit_Multi(); ``` ---
**Author:** ![RAc](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/rac/32/1389_2.png) [@RAc](https://forums.freertos.org/u/RAc)\ **Post date:** [August 18, 2023, 3:11pm UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/13 "2023-08-18T15:11:49Z")
You only have one interface but two end points? Wouldn’t you have seperate interfaces for each network card? As a side note, it looks like you are re using the same MAC address for both cards. That would be unrelated to your problem at hand but does not seem right nevertheless… ---
**Author:** ![ozanagma](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/ozanagma/32/3136_2.png) [@ozanagma](https://forums.freertos.org/u/ozanagma)\ **Post date:** [August 19, 2023, 1:20pm UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/14 "2023-08-19T13:20:40Z")
For now, I can continue like this, but I think this feature should be added. ---
**Author:** ![rtel](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/rtel/32/31_2.png) [@rtel](https://forums.freertos.org/u/rtel)\ **Post date:** [August 19, 2023, 8:35pm UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/15 "2023-08-19T20:35:49Z")
Yes - two identical MAC addresses on the same subnet is going to cause a problem. Which would respond to an ARP, for example. ---
**Author:** ![htibosch](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/htibosch/32/62_2.png) [@htibosch](https://forums.freertos.org/u/htibosch)\ **Post date:** [August 20, 2023, 6:56am UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/16 "2023-08-20T06:56:56Z")
A short comment at the end of this long topic: Within FreeRTOS+TCP, a port number can only be bound to one socket system wide. So for instance, you can open one HTTP socket at port 80, which will receive connections from all endpoints and all interfaces. And you can only bind one UDP socket to port 17000. This behaviour has been present in all earlier versions of +TCP /multi /IPv6, since about 2016. The reason for this choice was: - A simpler implementation - Lower memory foot print ( a socket is an “expensive” object ) - Simpler application code On Linux or Windows you can choose between binding to a particular IP address ( 192.168.2.11 ), or binding to the the ANY address 0.0.0.0. When binding to a particular address like 192.168.2.11:80, one can allow other TCP servers to re-use port 80 by setting the `SO_REUSEADDR` option on the socket. @rtel wrote: > For example, having an HTTP server on 10.10.10.10:80 and 1.2.3.4:80 at the same time. Exactly. @RAc wrote: > And you are sure that the IP addresses passed to the two constructors are distinct? In fact, the binding IP-address is ignored, only the port is what matters. > it looks like you are re using the same MAC address for both cards That is unfortunate, because that makes routing more difficult. On FreeRTOS+TCP, you can check the IP-addresses of both sides of a TCP connection with: ```auto BaseType_t FreeRTOS_GetRemoteAddress( ConstSocket_t xSocket, struct freertos_sockaddr * pxAddress ); size_t FreeRTOS_GetLocalAddress( ConstSocket_t xSocket, struct freertos_sockaddr * pxAddress ); ``` On the basis of this information, you can decide to offer a different type of website. Most of you will know: a TCP server socket doesn’t do much, it can create a local socket with the same port number as the server. > bind function because I use the same port number for both endpoints @ozanagma, Could you try the following? ```auto endpoint 1 : 192.168.1.100, mask 255.255.255.0 endpoint 2 : 192.168.2.100, mask 255.255.255.0 ``` Create a socket and bind it to port 17000. Now you can write to both endpoints and the routing should work well. When a device replies, you can find out who’s replying by checking the parameter `pxSourceAddress`. @rtel wrote: > Yes - two identical MAC addresses on the same subnet is going to cause a problem. Which would respond to an ARP, for example. That is another reason to give endpoint a unique netmask. If the above is impossible in your setup, lets think of finding a solution in the library. Thanks ---
**Author:** ![ozanagma](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/ozanagma/32/3136_2.png) [@ozanagma](https://forums.freertos.org/u/ozanagma)\ **Post date:** [August 21, 2023, 12:17pm UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/17 "2023-08-21T12:17:32Z")
Hi @htibosch, Thank you for your detailed answer. As I mentioned in my comment above, my main purpose is to pretend to run more than one card software on the same card, communicate them over ethernet and test the software. After failing to do what I wanted to do, I tried other configurations and using the same mac address was one of them. Actually, I do not intend to use the same mac address. So you can think of it as if I’m not using the same mac address. The main problem was this: I have a task and this task was sending a udp packet from a socket once in a while. I am not receiving any packets from this socket at all. I ran into this problem when I tried to run two different card software on the same card. I solved my own problem by increasing the port number of the second task by one. At this point, it was enough for me to know that the error I was getting was normal. The methods you suggest will be very useful for the problems I will encounter. This solved my problem and thank you for your help. Note: I solved the main problem(provide communication between two endpoints) by putting the loopback code you wrote, inside the **ZynqNetworkInterfaceOutput** function and making a few more changes. Also, thank you for the code you wrote. I will write about the problems I encountered while doing this in a new post. ---
**Author:** ![Shub](https://avatars.discourse-cdn.com/v4/letter/s/6f9a4e/32.png) [@Shub](https://forums.freertos.org/u/Shub)\ **Post date:** [August 21, 2023, 4:58pm UTC](https://forums.freertos.org/t/freertos-tcp-4-0-0-port-binding-problem/18010/18 "2023-08-21T16:58:29Z")
Thanks @ozanagma for the clarification. We will add this to our FreeRTOS-plus-TCP port number page ([TCP port and UDP port](https://freertos.org/FreeRTOS-Plus/FreeRTOS_Plus_TCP/port_number.html)).