# FreeRTOS - TCP/IP: UDP socket buffer size? **URL:** \ **Category:** Kernel\ **Created:** [May 28, 2018, 1:58pm UTC](https://forums.freertos.org/t/freertos-tcp-ip-udp-socket-buffer-size/7230 "2018-05-28T13:58:07Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![system](https://d2v6vdsk2p900z.cloudfront.net/original/1X/7fc8fdb729c645aab5b20282bbe34e57cb407be6.jpeg) [@system](https://forums.freertos.org/u/system)\ **Post date:** [May 28, 2018, 1:58pm UTC](https://forums.freertos.org/t/freertos-tcp-ip-udp-socket-buffer-size/7230/1 "2018-05-28T13:58:07Z")
**[kenchang1](https://sourceforge.net/u/kenchang1/)** wrote on [Monday, May 28, 2018](https://sourceforge.net/p/freertos/discussion/382005/thread/56c5de95/#a531): For TCP sockets I can find “ipconfigTCP\_RX\_BUFFER\_LENGTH” for the receive buffer size. Is there a similar parameter for UDP sockets? Or is it only this one: ipconfigNUM\_NETWORK\_BUFFER\_DESCRIPTORS ? regards, Ken ---
**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:** [May 28, 2018, 2:12pm UTC](https://forums.freertos.org/t/freertos-tcp-ip-udp-socket-buffer-size/7230/2 "2018-05-28T14:12:19Z")
**[heinbali01](https://sourceforge.net/u/heinbali01/)** wrote on [Monday, May 28, 2018](https://sourceforge.net/p/freertos/discussion/382005/thread/56c5de95/#4ddc): Interesting question! The number of UDP messages that you can receive without reading them, is indeed limited by `ipconfigNUM_NETWORK_BUFFER_DESCRIPTORS`. For TCP a circular “stream buffer” is created for each direction. TCP data must be buffered, and kept in a buffer until the transmission has been acknowledged by the peer. This TCP housekeeping of data is complicated. I tried to make clear how it works in 2 pictures ( attached to this post ). The implementation of UDP sockets is a lot simpler. It has a list ( `List_t` ) of Network Buffers that were received. Note that `FreeRTOS_recvfrom()` has a zero-copy possibility, so that you can peek directly into a Network Buffer. There is an important setting for UDP sockets, limiting the maximum number of received packets: ```auto #ifndef ipconfigUDP_MAX_RX_PACKETS /* Make positive to define the maximum number of packets * which will be buffered for each UDP socket. Can be * overridden with the socket option FREERTOS_SO_UDP_MAX_RX_PACKETS */ #define ipconfigUDP_MAX_RX_PACKETS 0u #endif ``` Suppose that you get a UDP attack: thousands of packets are fired to your UDP port, the attack will not disturb the device because at most `ipconfigUDP_MAX_RX_PACKETS` network buffers will be stored. ---
**Author:** ![system](https://d2v6vdsk2p900z.cloudfront.net/original/1X/7fc8fdb729c645aab5b20282bbe34e57cb407be6.jpeg) [@system](https://forums.freertos.org/u/system)\ **Post date:** [May 28, 2018, 2:46pm UTC](https://forums.freertos.org/t/freertos-tcp-ip-udp-socket-buffer-size/7230/3 "2018-05-28T14:46:31Z")
**[kenchang1](https://sourceforge.net/u/kenchang1/)** wrote on [Monday, May 28, 2018](https://sourceforge.net/p/freertos/discussion/382005/thread/56c5de95/#dea9): Hi Hein, Thanks for the answer. I have an additional question. How are these 2 parameters related, ipconfigUDP\_MAX\_RX\_PACKETS and ipconfigNUM\_NETWORK\_BUFFER\_DESCRIPTORS? When I increase ipconfigUDP\_MAX\_RX\_PACKETS from (3) to (10), I get an Assertion fail: “Assertion failed in file …/src/FreeRTOS-Plus-TCP-multi/FreeRTOS\_IP.c, line 1610”. Line 1610 of FreeRTOS\_IP.c is this part of the code: ```auto static void prvProcessEthernetPacket( NetworkBufferDescriptor_t * const pxNetworkBuffer ) { EthernetHeader_t *pxEthernetHeader; volatile eFrameProcessingResult_t eReturned; /* Volatile to prevent complier warnings when ipCONSIDER_FRAME_FOR_PROCESSING just sets it to eProcessBuffer. */ configASSERT( pxNetworkBuffer ); ``` regards, Ken ---
**Author:** ![system](https://d2v6vdsk2p900z.cloudfront.net/original/1X/7fc8fdb729c645aab5b20282bbe34e57cb407be6.jpeg) [@system](https://forums.freertos.org/u/system)\ **Post date:** [June 5, 2018, 12:12pm UTC](https://forums.freertos.org/t/freertos-tcp-ip-udp-socket-buffer-size/7230/4 "2018-06-05T12:12:28Z")
**[kenchang1](https://sourceforge.net/u/kenchang1/)** wrote on [Tuesday, June 05, 2018](https://sourceforge.net/p/freertos/discussion/382005/thread/56c5de95/#2811): The Assert fail was caused by 2 globally declared network pointer buffers in x\_emacpsif\_dma.c: ```auto static NetworkBufferDescriptor_t *ethMsg = NULL; static NetworkBufferDescriptor_t *ethLast = NULL; ``` Fixed by making them local. ---
**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:** [June 7, 2018, 2:14pm UTC](https://forums.freertos.org/t/freertos-tcp-ip-udp-socket-buffer-size/7230/5 "2018-06-07T14:14:19Z")
**[heinbali01](https://sourceforge.net/u/heinbali01/)** wrote on [Thursday, June 07, 2018](https://sourceforge.net/p/freertos/discussion/382005/thread/56c5de95/#8690): Ken, thanks a lot for your big effort to find the cause of this problem. The driver `x_emacpsif_dma.c` worked fine as long as it handled a single NIC. You found that when it serves two EMAC’s, corruption may occur. So the problem was only present in the **/multi** version. My stupid: two tasks were storing temporary data in common variables. These simple changes were made to avoid mentioned problem: Around line 320: ```auto -static NetworkBufferDescriptor_t *ethMsg = NULL; -static NetworkBufferDescriptor_t *ethLast = NULL; - -static void passEthMessages( ) +static void passEthMessages( NetworkBufferDescriptor_t *ethMsg ) ``` Around line 346: ```auto int emacps_check_rx( xemacpsif_s *xemacpsif ) { NetworkBufferDescriptor_t *pxBuffer, *pxNewBuffer; int rx_bytes; volatile int msgCount = 0; int head = xemacpsif->rxHead; BaseType_t bHasDataPacket = pdFALSE; +NetworkBufferDescriptor_t *ethMsg = NULL; +NetworkBufferDescriptor_t *ethLast = NULL; - passEthMessages( ); + passEthMessages( ethMsg ); ```