FreeRTOS-Plus-TCP/source/FreeRTOS_ARP.c

/*
 * FreeRTOS+TCP <DEVELOPMENT BRANCH>
 * Copyright (C) 2022 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
 *
 * SPDX-License-Identifier: MIT
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * http://aws.amazon.com/freertos
 * http://www.FreeRTOS.org
 */

/**
 * @file FreeRTOS_ARP.c
 * @brief Implements the Address Resolution Protocol for the FreeRTOS+TCP network stack.
 */

/* Standard includes. */
#include <stdint.h>
#include <stdio.h>

/* FreeRTOS includes. */
#include "FreeRTOS.h"
#include "task.h"
#include "queue.h"
#include "semphr.h"

/* FreeRTOS+TCP includes. */
#include "FreeRTOS_IP.h"
#include "FreeRTOS_IP_Timers.h"
#include "FreeRTOS_Sockets.h"
#include "FreeRTOS_IP_Private.h"
#include "FreeRTOS_ARP.h"
#include "FreeRTOS_UDP_IP.h"
#include "FreeRTOS_DHCP.h"
#if ( ipconfigUSE_LLMNR == 1 )
    #include "FreeRTOS_DNS.h"
#endif /* ipconfigUSE_LLMNR */
#include "NetworkBufferManagement.h"
#include "NetworkInterface.h"
#include "FreeRTOS_Routing.h"
#include "FreeRTOS_ND.h"


/** @brief When the age of an entry in the ARP table reaches this value (it counts down
 * to zero, so this is an old entry) an ARP request will be sent to see if the
 * entry is still valid and can therefore be refreshed. */
#define arpMAX_ARP_AGE_BEFORE_NEW_ARP_REQUEST    ( 3U )

/** @brief The time between gratuitous ARPs. */
#ifndef arpGRATUITOUS_ARP_PERIOD
    #define arpGRATUITOUS_ARP_PERIOD    ( pdMS_TO_TICKS( 20000U ) )
#endif

/** @brief When there is another device which has the same IP address as the IP address
 * of this device, a defensive ARP request should be sent out. However, according to
 * RFC 5227 section 1.1, there must be a minimum interval of 10 seconds between
 * consecutive defensive ARP packets. */
#ifndef arpIP_CLASH_RESET_TIMEOUT_MS
    #define arpIP_CLASH_RESET_TIMEOUT_MS    10000U
#endif

/** @brief Maximum number of defensive ARPs to be sent for an ARP clash per
 * arpIP_CLASH_RESET_TIMEOUT_MS period. The retries are limited to one as outlined
 * by RFC 5227 section 2.4 part b.*/
#ifndef arpIP_CLASH_MAX_RETRIES
    #define arpIP_CLASH_MAX_RETRIES    1U
#endif

/*
 * Lookup an MAC address in the ARP cache from the IP address.
 */
static eARPLookupResult_t prvCacheLookup( uint32_t ulAddressToLookup,
                                          MACAddress_t * const pxMACAddress,
                                          NetworkEndPoint_t ** ppxEndPoint );

static void vARPProcessPacketRequest( ARPPacket_t * pxARPFrame,
                                      NetworkEndPoint_t * pxTargetEndPoint,
                                      uint32_t ulSenderProtocolAddress );

static void vARPProcessPacketReply( const ARPPacket_t * pxARPFrame,
                                    NetworkEndPoint_t * pxTargetEndPoint,
                                    uint32_t ulSenderProtocolAddress );

static eARPLookupResult_t eARPGetCacheEntryGateWay( uint32_t * pulIPAddress,
                                                    MACAddress_t * const pxMACAddress,
                                                    struct xNetworkEndPoint ** ppxEndPoint );

static BaseType_t prvFindCacheEntry( const MACAddress_t * pxMACAddress,
                                     const uint32_t ulIPAddress,
                                     struct xNetworkEndPoint * pxEndPoint,
                                     CacheLocation_t * pxLocation );

/*-----------------------------------------------------------*/

/** @brief The ARP cache. */
_static ARPCacheRow_t xARPCache[ ipconfigARP_CACHE_ENTRIES ];

/** @brief  The time at which the last gratuitous ARP was sent.  Gratuitous ARPs are used
 * to ensure ARP tables are up to date and to detect IP address conflicts. */
static TickType_t xLastGratuitousARPTime = 0U;

/*
 * IP-clash detection is currently only used internally. When DHCP doesn't respond, the
 * driver can try out a random LinkLayer IP address (169.254.x.x).  It will send out a
 * gratuitous ARP message and, after a period of time, check the variables here below:
 */
#if ( ipconfigARP_USE_CLASH_DETECTION != 0 )
    /* Becomes non-zero if another device responded to a gratuitous ARP message. */
    BaseType_t xARPHadIPClash;
    /* MAC-address of the other device containing the same IP-address. */
    MACAddress_t xARPClashMacAddress;
#endif /* ipconfigARP_USE_CLASH_DETECTION */

/*-----------------------------------------------------------*/

/**
 * @brief Process the ARP packets.
 *
 * @param[in] pxNetworkBuffer: : The network buffer with the packet to be processed.
 *
 * @return An enum which says whether to return the frame or to release it.
 */
eFrameProcessingResult_t eARPProcessPacket( const NetworkBufferDescriptor_t * pxNetworkBuffer )
{
    /* MISRA Ref 11.3.1 [Misaligned access] */
    /* More details at: https://github.com/FreeRTOS/FreeRTOS-Plus-TCP/blob/main/MISRA.md#rule-113 */
    /* coverity[misra_c_2012_rule_11_3_violation] */
    ARPPacket_t * pxARPFrame = ( ( ARPPacket_t * ) pxNetworkBuffer->pucEthernetBuffer );
    eFrameProcessingResult_t eReturn = eReleaseBuffer;
    ARPHeader_t * pxARPHeader;
    uint32_t ulTargetProtocolAddress, ulSenderProtocolAddress;

    /* memcpy() helper variables for MISRA Rule 21.15 compliance*/
    const void * pvCopySource;
    void * pvCopyDest;
    NetworkEndPoint_t * pxTargetEndPoint = pxNetworkBuffer->pxEndPoint;

    /* Next defensive request must not be sent for arpIP_CLASH_RESET_TIMEOUT_MS
     * period. */
    static TickType_t uxARPClashTimeoutPeriod = pdMS_TO_TICKS( arpIP_CLASH_RESET_TIMEOUT_MS );

    /* This local variable is used to keep track of number of ARP requests sent and
     * also to limit the requests to arpIP_CLASH_MAX_RETRIES per arpIP_CLASH_RESET_TIMEOUT_MS
     * period. */
    static UBaseType_t uxARPClashCounter = 0U;
    /* The time at which the last ARP clash was sent. */
    static TimeOut_t xARPClashTimeOut;

    pxARPHeader = &( pxARPFrame->xARPHeader );

    /* Only Ethernet hardware type is supported.
     * Only IPv4 address can be present in the ARP packet.
     * The hardware length (the MAC address) must be 6 bytes. And,
     * The Protocol address length must be 4 bytes as it is IPv4. */
    if( ( pxARPHeader->usHardwareType == ipARP_HARDWARE_TYPE_ETHERNET ) &&
        ( pxARPHeader->usProtocolType == ipARP_PROTOCOL_TYPE ) &&
        ( pxARPHeader->ucHardwareAddressLength == ipMAC_ADDRESS_LENGTH_BYTES ) &&
        ( pxARPHeader->ucProtocolAddressLength == ipIP_ADDRESS_LENGTH_BYTES ) )
    {
        /* The field ucSenderProtocolAddress is badly aligned, copy byte-by-byte. */

        /*
         * Use helper variables for memcpy() to remain
         * compliant with MISRA Rule 21.15.  These should be
         * optimized away.
         */
        pvCopySource = pxARPHeader->ucSenderProtocolAddress;
        pvCopyDest = &ulSenderProtocolAddress;
        ( void ) memcpy( pvCopyDest, pvCopySource, sizeof( ulSenderProtocolAddress ) );
        /* The field ulTargetProtocolAddress is well-aligned, a 32-bits copy. */
        ulTargetProtocolAddress = pxARPHeader->ulTargetProtocolAddress;

        if( uxARPClashCounter != 0U )
        {
            /* Has the timeout been reached? */
            if( xTaskCheckForTimeOut( &xARPClashTimeOut, &uxARPClashTimeoutPeriod ) == pdTRUE )
            {
                /* We have waited long enough, reset the counter. */
                uxARPClashCounter = 0;
            }
        }

        /* Check whether the lowest bit of the highest byte is 1 to check for
         * multicast address or even a broadcast address (FF:FF:FF:FF:FF:FF). */
        if( ( pxARPHeader->xSenderHardwareAddress.ucBytes[ 0 ] & 0x01U ) == 0x01U )
        {
            /* Senders address is a multicast OR broadcast address which is not
             * allowed for an ARP packet. Drop the packet. See RFC 1812 section
             * 3.3.2. */
            iptraceDROPPED_INVALID_ARP_PACKET( pxARPHeader );
        }
        else if( ( ipFIRST_LOOPBACK_IPv4 <= ( FreeRTOS_ntohl( ulSenderProtocolAddress ) ) ) &&
                 ( ( FreeRTOS_ntohl( ulSenderProtocolAddress ) ) < ipLAST_LOOPBACK_IPv4 ) )
        {
            /* The local loopback addresses must never appear outside a host. See RFC 1122
             * section 3.2.1.3. */
            iptraceDROPPED_INVALID_ARP_PACKET( pxARPHeader );
        }
        /* Check whether there is a clash with another device for this IP address. */
        else if( ( pxTargetEndPoint != NULL ) && ( ulSenderProtocolAddress == pxTargetEndPoint->ipv4_settings.ulIPAddress ) )
        {
            if( uxARPClashCounter < arpIP_CLASH_MAX_RETRIES )
            {
                /* Increment the counter. */
                uxARPClashCounter++;

                /* Send out a defensive ARP request. */
                FreeRTOS_OutputARPRequest( pxTargetEndPoint->ipv4_settings.ulIPAddress );

                /* Since an ARP Request for this IP was just sent, do not send a gratuitous
                 * ARP for arpGRATUITOUS_ARP_PERIOD. */
                xLastGratuitousARPTime = xTaskGetTickCount();

                /* Note the time at which this request was sent. */
                vTaskSetTimeOutState( &xARPClashTimeOut );

                /* Reset the time-out period to the given value. */
                uxARPClashTimeoutPeriod = pdMS_TO_TICKS( arpIP_CLASH_RESET_TIMEOUT_MS );
            }

            /* Process received ARP frame to see if there is a clash. */
            #if ( ipconfigARP_USE_CLASH_DETECTION != 0 )
                {
                    NetworkEndPoint_t * pxSourceEndPoint = FreeRTOS_FindEndPointOnIP_IPv4( ulSenderProtocolAddress, 2 );

                    if( ( pxSourceEndPoint != NULL ) && ( pxSourceEndPoint->ipv4_settings.ulIPAddress == ulSenderProtocolAddress ) )
                    {
                        xARPHadIPClash = pdTRUE;
                        /* Remember the MAC-address of the other device which has the same IP-address. */
                        ( void ) memcpy( xARPClashMacAddress.ucBytes, pxARPHeader->xSenderHardwareAddress.ucBytes, sizeof( xARPClashMacAddress.ucBytes ) );
                    }
                }
            #endif /* ipconfigARP_USE_CLASH_DETECTION */
        }
        else
        {
            traceARP_PACKET_RECEIVED();

            /* Some extra logging while still testing. */
            #if ( ipconfigHAS_PRINTF != 0 )
                if( pxARPHeader->usOperation == ( uint16_t ) ipARP_REPLY )
                {
                    FreeRTOS_printf( ( "ipARP_REPLY from %xip to %xip end-point %xip\n",
                                       ( unsigned ) FreeRTOS_ntohl( ulSenderProtocolAddress ),
                                       ( unsigned ) FreeRTOS_ntohl( ulTargetProtocolAddress ),
                                       ( unsigned ) FreeRTOS_ntohl( ( pxTargetEndPoint != NULL ) ? pxTargetEndPoint->ipv4_settings.ulIPAddress : 0U ) ) );
                }
            #endif /* ( ipconfigHAS_DEBUG_PRINTF != 0 ) */

            #if ( ipconfigHAS_DEBUG_PRINTF != 0 )
                if( ( pxARPHeader->usOperation == ( uint16_t ) ipARP_REQUEST ) &&
                    ( ulSenderProtocolAddress != ulTargetProtocolAddress ) &&
                    ( pxTargetEndPoint != NULL ) )
                {
                    FreeRTOS_debug_printf( ( "ipARP_REQUEST from %xip to %xip end-point %xip\n",
                                             ( unsigned ) FreeRTOS_ntohl( ulSenderProtocolAddress ),
                                             ( unsigned ) FreeRTOS_ntohl( ulTargetProtocolAddress ),
                                             ( unsigned ) ( FreeRTOS_ntohl( ( pxTargetEndPoint != NULL ) ? pxTargetEndPoint->ipv4_settings.ulIPAddress : 0U ) ) ) );
                }
            #endif /* ( ipconfigHAS_PRINTF != 0 ) */

            /* ulTargetProtocolAddress won't be used unless logging is enabled. */
            ( void ) ulTargetProtocolAddress;

            /* Don't do anything if the local IP address is zero because
             * that means a DHCP request has not completed. */
            if( ( pxTargetEndPoint != NULL ) && ( pxTargetEndPoint->bits.bEndPointUp != pdFALSE_UNSIGNED ) )
            {
                switch( pxARPHeader->usOperation )
                {
                    case ipARP_REQUEST:

                        if( ( ulTargetProtocolAddress == pxTargetEndPoint->ipv4_settings.ulIPAddress ) &&
                            ( memcmp( ( void * ) pxTargetEndPoint->xMACAddress.ucBytes,
                                      ( void * ) ( pxARPHeader->xSenderHardwareAddress.ucBytes ),
                                      ipMAC_ADDRESS_LENGTH_BYTES ) != 0 ) )
                        {
                            vARPProcessPacketRequest( pxARPFrame, pxTargetEndPoint, ulSenderProtocolAddress );
                            eReturn = eReturnEthernetFrame;
                        }

                        break;

                    case ipARP_REPLY:
                        vARPProcessPacketReply( pxARPFrame, pxTargetEndPoint, ulSenderProtocolAddress );
                        break;

                    default:
                        /* Invalid. */
                        break;
                }
            }
        }
    }
    else
    {
        iptraceDROPPED_INVALID_ARP_PACKET( pxARPHeader );
    }

    return eReturn;
}
/*-----------------------------------------------------------*/

/**
 * @brief Process an ARP request packets.
 *
 * @param[in] pxARPFrame: the complete ARP-frame.
 * @param[in] pxTargetEndPoint: the end-point that handles the peer's address.
 * @param[in] ulSenderProtocolAddress: the IP-address of the sender.
 *
 */
static void vARPProcessPacketRequest( ARPPacket_t * pxARPFrame,
                                      NetworkEndPoint_t * pxTargetEndPoint,
                                      uint32_t ulSenderProtocolAddress )
{
    ARPHeader_t * pxARPHeader = &( pxARPFrame->xARPHeader );
    uint32_t ulTargetProtocolAddress = pxARPHeader->ulTargetProtocolAddress;
/* memcpy() helper variables for MISRA Rule 21.15 compliance*/
    const void * pvCopySource;
    void * pvCopyDest;


    /* The packet contained an ARP request.  Was it for the IP
     * address of one of the end-points? */
    /* It has been confirmed that pxTargetEndPoint is not NULL. */
    iptraceSENDING_ARP_REPLY( ulSenderProtocolAddress );

    /* The request is for the address of this node.  Add the
     * entry into the ARP cache, or refresh the entry if it
     * already exists. */
    vARPRefreshCacheEntry( &( pxARPHeader->xSenderHardwareAddress ), ulSenderProtocolAddress, pxTargetEndPoint );

    /* Generate a reply payload in the same buffer. */
    pxARPHeader->usOperation = ( uint16_t ) ipARP_REPLY;

    if( ulTargetProtocolAddress == ulSenderProtocolAddress )
    {
        /* A double IP address is detected! */
        /* Give the sources MAC address the value of the broadcast address, will be swapped later */

        /*
         * Use helper variables for memcpy() to remain
         * compliant with MISRA Rule 21.15.  These should be
         * optimized away.
         */
        pvCopySource = xBroadcastMACAddress.ucBytes;
        pvCopyDest = pxARPFrame->xEthernetHeader.xSourceAddress.ucBytes;
        ( void ) memcpy( pvCopyDest, pvCopySource, sizeof( xBroadcastMACAddress ) );

        ( void ) memset( pxARPHeader->xTargetHardwareAddress.ucBytes, 0, sizeof( MACAddress_t ) );
        pxARPHeader->ulTargetProtocolAddress = 0U;
    }
    else
    {
        /*
         * Use helper variables for memcpy() to remain
         * compliant with MISRA Rule 21.15.  These should be
         * optimized away.
         */
        pvCopySource = pxARPHeader->xSenderHardwareAddress.ucBytes;
        pvCopyDest = pxARPHeader->xTargetHardwareAddress.ucBytes;
        ( void ) memcpy( pvCopyDest, pvCopySource, sizeof( MACAddress_t ) );
        pxARPHeader->ulTargetProtocolAddress = ulSenderProtocolAddress;
    }

    /*
     * Use helper variables for memcpy() to remain
     * compliant with MISRA Rule 21.15.  These should be
     * optimized away.
     */
    pvCopySource = pxTargetEndPoint->xMACAddress.ucBytes;
    pvCopyDest = pxARPHeader->xSenderHardwareAddress.ucBytes;
    ( void ) memcpy( pvCopyDest, pvCopySource, sizeof( MACAddress_t ) );
    pvCopySource = &( pxTargetEndPoint->ipv4_settings.ulIPAddress );
    pvCopyDest = pxARPHeader->ucSenderProtocolAddress;
    ( void ) memcpy( pvCopyDest, pvCopySource, sizeof( pxARPHeader->ucSenderProtocolAddress ) );
}
/*-----------------------------------------------------------*/

/**
 * @brief A device has sent an ARP reply, process it.
 * @param[in] pxARPFrame: The ARP packet received.
 * @param[in] pxTargetEndPoint: The end-point on which it is received.
 * @param[in] ulSenderProtocolAddress: The IPv4 address involved.
 */
static void vARPProcessPacketReply( const ARPPacket_t * pxARPFrame,
                                    NetworkEndPoint_t * pxTargetEndPoint,
                                    uint32_t ulSenderProtocolAddress )
{
    const ARPHeader_t * pxARPHeader = &( pxARPFrame->xARPHeader );
    uint32_t ulTargetProtocolAddress = pxARPHeader->ulTargetProtocolAddress;

    /* If the packet is meant for this device or if the entry already exists. */
    if( ( ulTargetProtocolAddress == pxTargetEndPoint->ipv4_settings.ulIPAddress ) ||
        ( xIsIPInARPCache( ulSenderProtocolAddress ) == pdTRUE ) )
    {
        iptracePROCESSING_RECEIVED_ARP_REPLY( ulTargetProtocolAddress );
        vARPRefreshCacheEntry( &( pxARPHeader->xSenderHardwareAddress ), ulSenderProtocolAddress, pxTargetEndPoint );
    }

    if( ( pxARPWaitingNetworkBuffer != NULL ) &&
        ( uxIPHeaderSizePacket( pxARPWaitingNetworkBuffer ) == ipSIZE_OF_IPv4_HEADER ) )
    {
        /* MISRA Ref 11.3.1 [Misaligned access] */
/* More details at: https://github.com/FreeRTOS/FreeRTOS-Plus-TCP/blob/main/MISRA.md#rule-113 */
        /* coverity[misra_c_2012_rule_11_3_violation] */
        const IPPacket_t * pxARPWaitingIPPacket = ( ( IPPacket_t * ) pxARPWaitingNetworkBuffer->pucEthernetBuffer );
        const IPHeader_t * pxARPWaitingIPHeader = &( pxARPWaitingIPPacket->xIPHeader );

        if( ulSenderProtocolAddress == pxARPWaitingIPHeader->ulSourceIPAddress )
        {
            IPStackEvent_t xEventMessage;
            const TickType_t xDontBlock = ( TickType_t ) 0;

            xEventMessage.eEventType = eNetworkRxEvent;
            xEventMessage.pvData = ( void * ) pxARPWaitingNetworkBuffer;

            if( xSendEventStructToIPTask( &xEventMessage, xDontBlock ) != pdPASS )
            {
                /* Failed to send the message, so release the network buffer. */
                vReleaseNetworkBufferAndDescriptor( pxARPWaitingNetworkBuffer );
            }

            /* Clear the buffer. */
            pxARPWaitingNetworkBuffer = NULL;

            /* Found an ARP resolution, disable ARP resolution timer. */
            vIPSetARPResolutionTimerEnableState( pdFALSE );

            iptrace_DELAYED_ARP_REQUEST_REPLIED();
        }
    }
}
/*-----------------------------------------------------------*/

/**
 * @brief Check whether an IP address is in the ARP cache.
 *
 * @param[in] ulAddressToLookup: The 32-bit representation of an IP address to
 *                    check for.
 *
 * @return When the IP-address is found: pdTRUE, else pdFALSE.
 */
BaseType_t xIsIPInARPCache( uint32_t ulAddressToLookup )
{
    BaseType_t x, xReturn = pdFALSE;

    /* Loop through each entry in the ARP cache. */
    for( x = 0; x < ipconfigARP_CACHE_ENTRIES; x++ )
    {
        /* Does this row in the ARP cache table hold an entry for the IP address
         * being queried? */
        if( xARPCache[ x ].ulIPAddress == ulAddressToLookup )
        {
            xReturn = pdTRUE;

            /* A matching valid entry was found. */
            if( xARPCache[ x ].ucValid == ( uint8_t ) pdFALSE )
            {
                /* This entry is waiting an ARP reply, so is not valid. */
                xReturn = pdFALSE;
            }

            break;
        }
    }

    return xReturn;
}

/**
 * @brief Check whether a packet needs ARP resolution if it is on local subnet. If required send an ARP request.
 *
 * @param[in] pxNetworkBuffer: The network buffer with the packet to be checked.
 *
 * @return pdTRUE if the packet needs ARP resolution, pdFALSE otherwise.
 */
BaseType_t xCheckRequiresARPResolution( const NetworkBufferDescriptor_t * pxNetworkBuffer )
{
    BaseType_t xNeedsARPResolution = pdFALSE;

    if( uxIPHeaderSizePacket( pxNetworkBuffer ) == ipSIZE_OF_IPv6_HEADER )
    {
        const IPPacket_IPv6_t * pxIPPacket = ( ( IPPacket_IPv6_t * ) pxNetworkBuffer->pucEthernetBuffer );
        const IPHeader_IPv6_t * pxIPHeader = &( pxIPPacket->xIPHeader );
        IPv6_Address_t * pxIPAddress = &( pxIPHeader->xSourceAddress );
        uint8_t ucNextHeader = pxIPHeader->ucNextHeader;

        if( ( ucNextHeader == ipPROTOCOL_TCP ) ||
            ( ucNextHeader == ipPROTOCOL_UDP ) )
        {
            IPv6_Type_t eType = xIPv6_GetIPType( pxIPAddress );
            FreeRTOS_printf( ( "xCheckRequiresARPResolution: %pip type %s\n", pxIPAddress->ucBytes, ( eType == eIPv6_Global ) ? "Global" : ( eType == eIPv6_LinkLocal ) ? "LinkLocal" : "other" ) );

            if( eType == eIPv6_LinkLocal )
            {
                MACAddress_t xMACAddress;
                NetworkEndPoint_t * pxEndPoint;
                eARPLookupResult_t eResult;
                char pcName[ 80 ];

                eResult = eNDGetCacheEntry( pxIPAddress, &xMACAddress, &pxEndPoint );
                FreeRTOS_printf( ( "xCheckRequiresARPResolution: eResult %s with EP %s\n", ( eResult == eARPCacheMiss ) ? "Miss" : ( eResult == eARPCacheHit ) ? "Hit" : "Error", pcEndpointName( pxEndPoint, pcName, sizeof pcName ) ) );

                if( eResult == eARPCacheMiss )
                {
                    NetworkBufferDescriptor_t * pxTempBuffer;
                    size_t uxNeededSize;

                    uxNeededSize = ipSIZE_OF_ETH_HEADER + ipSIZE_OF_IPv6_HEADER + sizeof( ICMPRouterSolicitation_IPv6_t );
                    pxTempBuffer = pxGetNetworkBufferWithDescriptor( BUFFER_FROM_WHERE_CALL( 199 ) uxNeededSize, 0U );

                    if( pxTempBuffer != NULL )
                    {
                        pxTempBuffer->pxEndPoint = pxNetworkBuffer->pxEndPoint;
                        pxTempBuffer->pxInterface = pxNetworkBuffer->pxInterface;
                        vNDSendNeighbourSolicitation( pxNetworkBuffer, pxIPAddress );
                    }

                    xNeedsARPResolution = pdTRUE;
                }
            }
        }
    }
    else
    {
        /* MISRA Ref 11.3.1 [Misaligned access] */
        /* More details at: https://github.com/FreeRTOS/FreeRTOS-Plus-TCP/blob/main/MISRA.md#rule-113 */
        /* coverity[misra_c_2012_rule_11_3_violation] */
        const IPPacket_t * pxIPPacket = ( ( IPPacket_t * ) pxNetworkBuffer->pucEthernetBuffer );
        const IPHeader_t * pxIPHeader = &( pxIPPacket->xIPHeader );
        IPV4Parameters_t * pxIPv4Settings = &( pxNetworkBuffer->pxEndPoint->ipv4_settings );

        if( ( pxIPHeader->ulSourceIPAddress & pxIPv4Settings->ulNetMask ) == ( pxIPv4Settings->ulIPAddress & pxIPv4Settings->ulNetMask ) )
        {
            /* If the IP is on the same subnet and we do not have an ARP entry already,
             * then we should send out ARP for finding the MAC address. */
            if( xIsIPInARPCache( pxIPHeader->ulSourceIPAddress ) == pdFALSE )
            {
                FreeRTOS_OutputARPRequest( pxIPHeader->ulSourceIPAddress );

                /* This packet needs resolution since this is on the same subnet
                 * but not in the ARP cache. */
                xNeedsARPResolution = pdTRUE;
            }
        }
    }

    return xNeedsARPResolution;
}

#if ( ipconfigUSE_ARP_REMOVE_ENTRY != 0 )

/**
 * @brief Remove an ARP cache entry that matches with .pxMACAddress.
 *
 * @param[in] pxMACAddress: Pointer to the MAC address whose entry shall
 *                          be removed..
 * @return When the entry was found and remove: the IP-address, otherwise zero.
 */
    uint32_t ulARPRemoveCacheEntryByMac( const MACAddress_t * pxMACAddress )
    {
        BaseType_t x;
        uint32_t lResult = 0;

        configASSERT( pxMACAddress != NULL );

        /* For each entry in the ARP cache table. */
        for( x = 0; x < ipconfigARP_CACHE_ENTRIES; x++ )
        {
            if( ( memcmp( xARPCache[ x ].xMACAddress.ucBytes, pxMACAddress->ucBytes, sizeof( pxMACAddress->ucBytes ) ) == 0 ) )
            {
                lResult = xARPCache[ x ].ulIPAddress;
                ( void ) memset( &xARPCache[ x ], 0, sizeof( xARPCache[ x ] ) );
                break;
            }
        }

        return lResult;
    }

#endif /* ipconfigUSE_ARP_REMOVE_ENTRY != 0 */
/*-----------------------------------------------------------*/

/**
 * @brief Add/update the ARP cache entry MAC-address to IP-address mapping.
 *
 * @param[in] pxMACAddress: Pointer to the MAC address whose mapping is being
 *                          updated.
 * @param[in] ulIPAddress: 32-bit representation of the IP-address whose mapping
 *                         is being updated.
 * @param[in] pxEndPoint: The end-point stored in the table.
 */
void vARPRefreshCacheEntry( const MACAddress_t * pxMACAddress,
                            const uint32_t ulIPAddress,
                            struct xNetworkEndPoint * pxEndPoint )
{
    #if ( ipconfigARP_STORES_REMOTE_ADDRESSES == 0 )
        /* Only process the IP address if it is on the local network. */
        BaseType_t xAddressIsLocal = ( FreeRTOS_FindEndPointOnNetMask( ulIPAddress, 2 ) != NULL ) ? 1 : 0; /* ARP remote address. */

        /* Only process the IP address if it matches with one of the end-points. */
        if( xAddressIsLocal != 0 )
    #else

        /* If ipconfigARP_STORES_REMOTE_ADDRESSES is non-zero, IP addresses with
         * a different netmask will also be stored.  After when replying to a UDP
         * message from a different netmask, the IP address can be looped up and a
         * reply sent.  This option is useful for systems with multiple gateways,
         * the reply will surely arrive.  If ipconfigARP_STORES_REMOTE_ADDRESSES is
         * zero the the gateway address is the only option. */

        if( pdTRUE )
    #endif
    {
        CacheLocation_t xLocation;
        BaseType_t xReady;

        xReady = prvFindCacheEntry( pxMACAddress, ulIPAddress, pxEndPoint, &( xLocation ) );

        if( xReady == pdFALSE )
        {
            if( xLocation.xMacEntry >= 0 )
            {
                xLocation.xUseEntry = xLocation.xMacEntry;

                if( xLocation.xIpEntry >= 0 )
                {
                    /* Both the MAC address as well as the IP address were found in
                     * different locations: clear the entry which matches the
                     * IP-address */
                    ( void ) memset( &( xARPCache[ xLocation.xIpEntry ] ), 0, sizeof( ARPCacheRow_t ) );
                }
            }
            else if( xLocation.xIpEntry >= 0 )
            {
                /* An entry containing the IP-address was found, but it had a different MAC address */
                xLocation.xUseEntry = xLocation.xIpEntry;
            }
            else
            {
                /* No matching entry found. */
            }

            /* If the entry was not found, we use the oldest entry and set the IPaddress */
            xARPCache[ xLocation.xUseEntry ].ulIPAddress = ulIPAddress;

            if( pxMACAddress != NULL )
            {
                ( void ) memcpy( xARPCache[ xLocation.xUseEntry ].xMACAddress.ucBytes, pxMACAddress->ucBytes, sizeof( pxMACAddress->ucBytes ) );

                iptraceARP_TABLE_ENTRY_CREATED( ulIPAddress, ( *pxMACAddress ) );
                /* And this entry does not need immediate attention */
                xARPCache[ xLocation.xUseEntry ].ucAge = ( uint8_t ) ipconfigMAX_ARP_AGE;
                xARPCache[ xLocation.xUseEntry ].ucValid = ( uint8_t ) pdTRUE;
                xARPCache[ xLocation.xUseEntry ].pxEndPoint = pxEndPoint;
            }
            else if( xLocation.xIpEntry < 0 )
            {
                xARPCache[ xLocation.xUseEntry ].ucAge = ( uint8_t ) ipconfigMAX_ARP_RETRANSMISSIONS;
                xARPCache[ xLocation.xUseEntry ].ucValid = ( uint8_t ) pdFALSE;
            }
            else
            {
                /* Nothing will be stored. */
            }
        }
    }
}
/*-----------------------------------------------------------*/

/**
 * @brief The results of an ARP look-up shall be stored in the ARP cache.
 *        This helper function looks up the location.
 * @param[in] pxMACAddress: The MAC-address belonging to the IP-address.
 * @param[in] ulIPAddress: The IP-address of the entry.
 * @param[in] pxEndPoint: The end-point that will stored in the table.
 * @param[out] pxLocation: The results of this search are written in this struct.
 */
static BaseType_t prvFindCacheEntry( const MACAddress_t * pxMACAddress,
                                     const uint32_t ulIPAddress,
                                     struct xNetworkEndPoint * pxEndPoint,
                                     CacheLocation_t * pxLocation )
{
    BaseType_t x = 0;
    uint8_t ucMinAgeFound = 0U;
    BaseType_t xReturn = pdFALSE;

    #if ( ipconfigARP_STORES_REMOTE_ADDRESSES != 0 )
        BaseType_t xAddressIsLocal = ( FreeRTOS_FindEndPointOnNetMask( ulIPAddress, 2 ) != NULL ) ? 1 : 0; /* ARP remote address. */
    #endif

    /* Start with the maximum possible number. */
    ucMinAgeFound--;

    pxLocation->xIpEntry = -1;
    pxLocation->xMacEntry = -1;
    pxLocation->xUseEntry = 0;

    /* For each entry in the ARP cache table. */
    for( x = 0; x < ipconfigARP_CACHE_ENTRIES; x++ )
    {
        BaseType_t xMatchingMAC = pdFALSE;

        if( pxMACAddress != NULL )
        {
            if( memcmp( xARPCache[ x ].xMACAddress.ucBytes, pxMACAddress->ucBytes, sizeof( pxMACAddress->ucBytes ) ) == 0 )
            {
                xMatchingMAC = pdTRUE;
            }
        }

        /* Does this line in the cache table hold an entry for the IP
         * address being queried? */
        if( xARPCache[ x ].ulIPAddress == ulIPAddress )
        {
            if( pxMACAddress == NULL )
            {
                /* In case the parameter pxMACAddress is NULL, an entry will be reserved to
                 * indicate that there is an outstanding ARP request, This entry will have
                 * "ucValid == pdFALSE". */
                pxLocation->xIpEntry = x;
                break;
            }

            /* See if the MAC-address also matches. */
            if( xMatchingMAC != pdFALSE )
            {
                /* This function will be called for each received packet
                 * This is by far the most common path. */
                xARPCache[ x ].ucAge = ( uint8_t ) ipconfigMAX_ARP_AGE;
                xARPCache[ x ].ucValid = ( uint8_t ) pdTRUE;
                xARPCache[ x ].pxEndPoint = pxEndPoint;
                /* Indicate to the caller that the entry is updated. */
                xReturn = pdTRUE;
                break;
            }

            /* Found an entry containing ulIPAddress, but the MAC address
             * doesn't match.  Might be an entry with ucValid=pdFALSE, waiting
             * for an ARP reply.  Still want to see if there is match with the
             * given MAC address.ucBytes.  If found, either of the two entries
             * must be cleared. */
            pxLocation->xIpEntry = x;
        }
        else if( xMatchingMAC != pdFALSE )
        {
            /* Found an entry with the given MAC-address, but the IP-address
             * is different.  Continue looping to find a possible match with
             * ulIPAddress. */
            #if ( ipconfigARP_STORES_REMOTE_ADDRESSES != 0 )
                {
                    /* If ARP stores the MAC address of IP addresses outside the
                     * network, than the MAC address of the gateway should not be
                     * overwritten. */
                    BaseType_t xOtherIsLocal = ( FreeRTOS_FindEndPointOnNetMask( xARPCache[ x ].ulIPAddress, 3 ) != NULL ) ? 1 : 0; /* ARP remote address. */

                    if( xAddressIsLocal == xOtherIsLocal )
                    {
                        pxLocation->xMacEntry = x;
                    }
                }
            #else /* if ( ipconfigARP_STORES_REMOTE_ADDRESSES != 0 ) */
                {
                    pxLocation->xMacEntry = x;
                }
            #endif /* if ( ipconfigARP_STORES_REMOTE_ADDRESSES != 0 ) */
        }

        /* _HT_
         * Shouldn't we test for xARPCache[ x ].ucValid == pdFALSE here ? */
        else if( xARPCache[ x ].ucAge < ucMinAgeFound )
        {
            /* As the table is traversed, remember the table row that
             * contains the oldest entry (the lowest age count, as ages are
             * decremented to zero) so the row can be re-used if this function
             * needs to add an entry that does not already exist. */
            ucMinAgeFound = xARPCache[ x ].ucAge;
            pxLocation->xUseEntry = x;
        }
        else
        {
            /* Nothing happens to this cache entry for now. */
        }
    } /* for( x = 0; x < ipconfigARP_CACHE_ENTRIES; x++ ) */

    return xReturn;
}
/*-----------------------------------------------------------*/

#if ( ipconfigUSE_ARP_REVERSED_LOOKUP == 1 )

/**
 * @brief Retrieve an entry from the cache table
 *
 * @param[in] pxMACAddress: The MAC-address of the entry of interest.
 * @param[out] pulIPAddress: set to the IP-address found, or unchanged when not found.
 *
 * @return Either eARPCacheMiss or eARPCacheHit.
 */
    eARPLookupResult_t eARPGetCacheEntryByMac( const MACAddress_t * const pxMACAddress,
                                               uint32_t * pulIPAddress,
                                               struct xNetworkInterface ** ppxInterface )
    {
        BaseType_t x;
        eARPLookupResult_t eReturn = eARPCacheMiss;

        configASSERT( pxMACAddress != NULL );
        configASSERT( pulIPAddress != NULL );

        if( ppxInterface != NULL )
        {
            *( ppxInterface ) = NULL;
        }

        /* Loop through each entry in the ARP cache. */
        for( x = 0; x < ipconfigARP_CACHE_ENTRIES; x++ )
        {
            /* Does this row in the ARP cache table hold an entry for the MAC
             * address being searched? */
            if( memcmp( pxMACAddress->ucBytes, xARPCache[ x ].xMACAddress.ucBytes, sizeof( MACAddress_t ) ) == 0 )
            {
                *pulIPAddress = xARPCache[ x ].ulIPAddress;

                if( ( ppxInterface != NULL ) &&
                    ( xARPCache[ x ].pxEndPoint != NULL ) )
                {
                    *( ppxInterface ) = xARPCache[ x ].pxEndPoint->pxNetworkInterface;
                }

                eReturn = eARPCacheHit;
                break;
            }
        }

        return eReturn;
    }
#endif /* ipconfigUSE_ARP_REVERSED_LOOKUP */

/*-----------------------------------------------------------*/

/**
 * @brief Look for ulIPAddress in the ARP cache.
 *
 * @param[in,out] pulIPAddress: Pointer to the IP-address to be queried to the ARP cache.
 * @param[in,out] pxMACAddress: Pointer to a MACAddress_t variable where the MAC address
 *                          will be stored, if found.
 * @param[out] ppxEndPoint: Pointer to the end-point of the gateway will be stored.
 *
 * @return If the IP address exists, copy the associated MAC address into pxMACAddress,
 *         refresh the ARP cache entry's age, and return eARPCacheHit. If the IP
 *         address does not exist in the ARP cache return eARPCacheMiss. If the packet
 *         cannot be sent for any reason (maybe DHCP is still in process, or the
 *         addressing needs a gateway but there isn't a gateway defined) then return
 *         eCantSendPacket.
 */
eARPLookupResult_t eARPGetCacheEntry( uint32_t * pulIPAddress,
                                      MACAddress_t * const pxMACAddress,
                                      struct xNetworkEndPoint ** ppxEndPoint )
{
    eARPLookupResult_t eReturn;
    uint32_t ulAddressToLookup;
    NetworkEndPoint_t * pxEndPoint = NULL;

    configASSERT( pxMACAddress != NULL );
    configASSERT( pulIPAddress != NULL );
    configASSERT( ppxEndPoint != NULL );

    *( ppxEndPoint ) = NULL;
    ulAddressToLookup = *pulIPAddress;
    pxEndPoint = FreeRTOS_FindEndPointOnIP_IPv4( ulAddressToLookup, 0 );

    if( xIsIPv4Multicast( ulAddressToLookup ) != 0 )
    {
        /* Get the lowest 23 bits of the IP-address. */
        vSetMultiCastIPv4MacAddress( ulAddressToLookup, pxMACAddress );

        eReturn = eCantSendPacket;
        pxEndPoint = FreeRTOS_FirstEndPoint( NULL );

        for( ;
             pxEndPoint != NULL;
             pxEndPoint = FreeRTOS_NextEndPoint( NULL, pxEndPoint ) )
        {
            if( ENDPOINT_IS_IPv4( pxEndPoint ) )
            {
                /* For multi-cast, use the first IPv4 end-point. */
                *( ppxEndPoint ) = pxEndPoint;
                eReturn = eARPCacheHit;
                break;
            }
        }
    }
    else if( ( FreeRTOS_htonl( ulAddressToLookup ) & 0xffU ) == 0xffU ) /* Is this a broadcast address like x.x.x.255 ? */
    {
        /* This is a broadcast so it uses the broadcast MAC address. */
        ( void ) memcpy( pxMACAddress->ucBytes, xBroadcastMACAddress.ucBytes, sizeof( MACAddress_t ) );
        pxEndPoint = FreeRTOS_FindEndPointOnNetMask( ulAddressToLookup, 4 );

        if( pxEndPoint != NULL )
        {
            *( ppxEndPoint ) = pxEndPoint;
        }

        eReturn = eARPCacheHit;
    }
    else
    {
        eReturn = eARPGetCacheEntryGateWay( pulIPAddress, pxMACAddress, ppxEndPoint );
    }

    return eReturn;
}
/*-----------------------------------------------------------*/

/**
 * @brief The IPv4 address is apparently a web-address. Find a gateway..
 * @param[in] pulIPAddress: The target IP-address. It may be replaced with the IP
 *                          address of a gateway.
 * @param[in] pxMACAddress: In case the MAC-address is found in cache, it will be
 *                          stored to the buffer provided.
 * @param[out] ppxEndPoint: The end-point of the gateway will be copy to the pointee.
 */
static eARPLookupResult_t eARPGetCacheEntryGateWay( uint32_t * pulIPAddress,
                                                    MACAddress_t * const pxMACAddress,
                                                    struct xNetworkEndPoint ** ppxEndPoint )
{
    eARPLookupResult_t eReturn = eARPCacheMiss;
    uint32_t ulAddressToLookup = *( pulIPAddress );
    NetworkEndPoint_t * pxEndPoint;
    uint32_t ulOrginal = *pulIPAddress;

    /* It is assumed that devices with the same netmask are on the same
     * LAN and don't need a gateway. */
    pxEndPoint = FreeRTOS_FindEndPointOnNetMask( ulAddressToLookup, 4 );

    if( pxEndPoint == NULL )
    {
        /* No matching end-point is found, look for a gateway. */
        #if ( ipconfigARP_STORES_REMOTE_ADDRESSES == 1 )
            eReturn = prvCacheLookup( ulAddressToLookup, pxMACAddress, ppxEndPoint );

            if( eReturn == eARPCacheHit )
            {
                /* The stack is configured to store 'remote IP addresses', i.e. addresses
                 * belonging to a different the netmask.  prvCacheLookup() returned a hit, so
                 * the MAC address is known. */
            }
            else
        #endif
        {
            /* The IP address is off the local network, so look up the
             * hardware address of the router, if any. */
            *( ppxEndPoint ) = FreeRTOS_FindGateWay( ( BaseType_t ) ipTYPE_IPv4 );

            if( *( ppxEndPoint ) != NULL )
            {
                /* 'ipv4_settings' can be accessed safely, because 'ipTYPE_IPv4' was provided. */
                ulAddressToLookup = ( *ppxEndPoint )->ipv4_settings.ulGatewayAddress;
            }
            else
            {
                ulAddressToLookup = *pulIPAddress;
            }

            /*FreeRTOS_printf( ( "Using gateway %lxip\n", FreeRTOS_ntohl( ulAddressToLookup ) ) ); */
        }
    }
    else
    {
        /* The IP address is on the local network, so lookup the requested
         * IP address directly. */
        ulAddressToLookup = *pulIPAddress;
        *ppxEndPoint = pxEndPoint;
    }

    #if ( ipconfigARP_STORES_REMOTE_ADDRESSES == 1 )
        if( eReturn == eARPCacheMiss )
    #endif
    {
        if( ulAddressToLookup == 0U )
        {
            /* The address is not on the local network, and there is not a
             * router. */
            eReturn = eCantSendPacket;
        }
        else
        {
            eReturn = prvCacheLookup( ulAddressToLookup, pxMACAddress, ppxEndPoint );

            if( ( eReturn != eARPCacheHit ) || ( ulOrginal != ulAddressToLookup ) )
            {
                FreeRTOS_debug_printf( ( "ARP %xip %s using %xip\n",
                                         ( unsigned ) FreeRTOS_ntohl( ulOrginal ),
                                         ( eReturn == eARPCacheHit ) ? "hit" : "miss",
                                         ( unsigned ) FreeRTOS_ntohl( ulAddressToLookup ) ) );
            }

            /* It might be that the ARP has to go to the gateway. */
            *pulIPAddress = ulAddressToLookup;
        }
    }

    return eReturn;
}
/*-----------------------------------------------------------*/

/**
 * @brief Lookup an IP address in the ARP cache.
 *
 * @param[in] ulAddressToLookup: The 32-bit representation of an IP address to
 *                               lookup.
 * @param[out] pxMACAddress: A pointer to MACAddress_t variable where, if there
 *                          is an ARP cache hit, the MAC address corresponding to
 *                          the IP address will be stored.
 * @param[in,out] ppxEndPoint: a pointer to the end-point will be stored.
 *
 * @return When the IP-address is found: eARPCacheHit, when not found: eARPCacheMiss,
 *         and when waiting for a ARP reply: eCantSendPacket.
 */
static eARPLookupResult_t prvCacheLookup( uint32_t ulAddressToLookup,
                                          MACAddress_t * const pxMACAddress,
                                          NetworkEndPoint_t ** ppxEndPoint )
{
    BaseType_t x;
    eARPLookupResult_t eReturn = eARPCacheMiss;

    /* Loop through each entry in the ARP cache. */
    for( x = 0; x < ipconfigARP_CACHE_ENTRIES; x++ )
    {
        /* Does this row in the ARP cache table hold an entry for the IP address
         * being queried? */
        if( xARPCache[ x ].ulIPAddress == ulAddressToLookup )
        {
            /* A matching valid entry was found. */
            if( xARPCache[ x ].ucValid == ( uint8_t ) pdFALSE )
            {
                /* This entry is waiting an ARP reply, so is not valid. */
                eReturn = eCantSendPacket;
            }
            else
            {
                /* A valid entry was found. */
                ( void ) memcpy( pxMACAddress->ucBytes, xARPCache[ x ].xMACAddress.ucBytes, sizeof( MACAddress_t ) );
                /* ppxEndPoint != NULL was tested in the only caller eARPGetCacheEntry(). */
                *( ppxEndPoint ) = xARPCache[ x ].pxEndPoint;
                eReturn = eARPCacheHit;
            }

            break;
        }
    }

    return eReturn;
}
/*-----------------------------------------------------------*/

/**
 * @brief A call to this function will update (or 'Age') the ARP cache entries.
 *        The function will also try to prevent a removal of entry by sending
 *        an ARP query. It will also check whether we are waiting on an ARP
 *        reply - if we are, then an ARP request will be re-sent.
 *        In case an ARP entry has 'Aged' to 0, it will be removed from the ARP
 *        cache.
 */
void vARPAgeCache( void )
{
    BaseType_t x;
    TickType_t xTimeNow;

    /* Loop through each entry in the ARP cache. */
    for( x = 0; x < ipconfigARP_CACHE_ENTRIES; x++ )
    {
        /* If the entry is valid (its age is greater than zero). */
        if( xARPCache[ x ].ucAge > 0U )
        {
            /* Decrement the age value of the entry in this ARP cache table row.
             * When the age reaches zero it is no longer considered valid. */
            ( xARPCache[ x ].ucAge )--;

            /* If the entry is not yet valid, then it is waiting an ARP
             * reply, and the ARP request should be retransmitted. */
            if( xARPCache[ x ].ucValid == ( uint8_t ) pdFALSE )
            {
                FreeRTOS_OutputARPRequest( xARPCache[ x ].ulIPAddress );
            }
            else if( xARPCache[ x ].ucAge <= ( uint8_t ) arpMAX_ARP_AGE_BEFORE_NEW_ARP_REQUEST )
            {
                /* This entry will get removed soon.  See if the MAC address is
                 * still valid to prevent this happening. */
                iptraceARP_TABLE_ENTRY_WILL_EXPIRE( xARPCache[ x ].ulIPAddress );
                FreeRTOS_OutputARPRequest( xARPCache[ x ].ulIPAddress );
            }
            else
            {
                /* The age has just ticked down, with nothing to do. */
            }

            if( xARPCache[ x ].ucAge == 0U )
            {
                /* The entry is no longer valid.  Wipe it out. */
                iptraceARP_TABLE_ENTRY_EXPIRED( xARPCache[ x ].ulIPAddress );
                xARPCache[ x ].ulIPAddress = 0U;
            }
        }
    }

    xTimeNow = xTaskGetTickCount();

    if( ( xLastGratuitousARPTime == ( TickType_t ) 0 ) || ( ( xTimeNow - xLastGratuitousARPTime ) > ( TickType_t ) arpGRATUITOUS_ARP_PERIOD ) )
    {
        NetworkEndPoint_t * pxEndPoint = pxNetworkEndPoints;

        while( pxEndPoint != NULL )
        {
            if( ( pxEndPoint->bits.bEndPointUp != pdFALSE_UNSIGNED ) && ( pxEndPoint->ipv4_settings.ulIPAddress != 0U ) )
            {
                if( pxEndPoint->bits.bIPv6 != pdFALSE_UNSIGNED )
                {
                    FreeRTOS_OutputAdvertiseIPv6( pxEndPoint );
                }
                else
                {
                    if( pxEndPoint->ipv4_settings.ulIPAddress != 0U )
                    {
                        FreeRTOS_OutputARPRequest( pxEndPoint->ipv4_settings.ulIPAddress );
                    }
                }
            }

            pxEndPoint = pxEndPoint->pxNext;
        }

        xLastGratuitousARPTime = xTimeNow;
    }
}
/*-----------------------------------------------------------*/

/**
 * @brief Send a Gratuitous ARP packet to allow this node to announce the IP-MAC
 *        mapping to the entire network.
 */
void vARPSendGratuitous( void )
{
    /* Setting xLastGratuitousARPTime to 0 will force a gratuitous ARP the next
     * time vARPAgeCache() is called. */
    xLastGratuitousARPTime = ( TickType_t ) 0;

    /* Let the IP-task call vARPAgeCache(). */
    ( void ) xSendEventToIPTask( eARPTimerEvent );
}

/*-----------------------------------------------------------*/

/**
 * @brief Create and send an ARP request packet.
 *
 * @param[in] ulIPAddress: A 32-bit representation of the IP-address whose
 *                         physical (MAC) address is required.
 */
void FreeRTOS_OutputARPRequest( uint32_t ulIPAddress )
{
    NetworkBufferDescriptor_t * pxNetworkBuffer;
    const NetworkEndPoint_t * pxEndPoint;

    /* Send an ARP request to every end-point which has the type IPv4,
     * and which already has an IP-address assigned. */
    for( pxEndPoint = FreeRTOS_FirstEndPoint( NULL );
         pxEndPoint != NULL;
         pxEndPoint = FreeRTOS_NextEndPoint( NULL, pxEndPoint ) )
    {
        if( ( pxEndPoint->bits.bIPv6 == pdFALSE_UNSIGNED ) &&
            ( pxEndPoint->ipv4_settings.ulIPAddress != 0U ) )
        {
            /* This is called from the context of the IP event task, so a block time
             * must not be used. */
            pxNetworkBuffer = pxGetNetworkBufferWithDescriptor( sizeof( ARPPacket_t ), ( TickType_t ) 0U );

            if( pxNetworkBuffer != NULL )
            {
                pxNetworkBuffer->xIPAddress.ulIP_IPv4 = ulIPAddress;
                pxNetworkBuffer->pxEndPoint = pxEndPoint;
                pxNetworkBuffer->pxInterface = pxEndPoint->pxNetworkInterface;
                vARPGenerateRequestPacket( pxNetworkBuffer );

                #if ( ipconfigETHERNET_MINIMUM_PACKET_BYTES > 0 )
                    {
                        if( pxNetworkBuffer->xDataLength < ( size_t ) ipconfigETHERNET_MINIMUM_PACKET_BYTES )
                        {
                            BaseType_t xIndex;

                            for( xIndex = ( BaseType_t ) pxNetworkBuffer->xDataLength; xIndex < ( BaseType_t ) ipconfigETHERNET_MINIMUM_PACKET_BYTES; xIndex++ )
                            {
                                pxNetworkBuffer->pucEthernetBuffer[ xIndex ] = 0U;
                            }

                            pxNetworkBuffer->xDataLength = ( size_t ) ipconfigETHERNET_MINIMUM_PACKET_BYTES;
                        }
                    }
                #endif /* if( ipconfigETHERNET_MINIMUM_PACKET_BYTES > 0 ) */

                if( xIsCallingFromIPTask() != pdFALSE )
                {
                    iptraceNETWORK_INTERFACE_OUTPUT( pxNetworkBuffer->xDataLength, pxNetworkBuffer->pucEthernetBuffer );

                    /* Only the IP-task is allowed to call this function directly. */
                    if( pxEndPoint->pxNetworkInterface != NULL )
                    {
                        ( void ) pxEndPoint->pxNetworkInterface->pfOutput( pxEndPoint->pxNetworkInterface, pxNetworkBuffer, pdTRUE );
                    }
                }
                else
                {
                    IPStackEvent_t xSendEvent;

                    /* Send a message to the IP-task to send this ARP packet. */
                    xSendEvent.eEventType = eNetworkTxEvent;
                    xSendEvent.pvData = pxNetworkBuffer;

                    if( xSendEventStructToIPTask( &xSendEvent, ( TickType_t ) portMAX_DELAY ) == pdFAIL )
                    {
                        /* Failed to send the message, so release the network buffer. */
                        vReleaseNetworkBufferAndDescriptor( pxNetworkBuffer );
                    }
                }
            }
        }
    }
}
/*-----------------------------------------------------------*/

/**
 * @brief  Wait for address resolution: look-up the IP-address in the ARP-cache, and if
 *         needed send an ARP request, and wait for a reply.  This function is useful when
 *         called before FreeRTOS_sendto().
 *
 * @param[in] ulIPAddress: The IP-address to look-up.
 * @param[in] uxTicksToWait: The maximum number of clock ticks to wait for a reply.
 *
 * @return Zero when successful.
 */
BaseType_t xARPWaitResolution( uint32_t ulIPAddress,
                               TickType_t uxTicksToWait )
{
    BaseType_t xResult = -pdFREERTOS_ERRNO_EADDRNOTAVAIL;
    TimeOut_t xTimeOut;
    MACAddress_t xMACAddress;
    eARPLookupResult_t xLookupResult;
    NetworkEndPoint_t * pxEndPoint;
    size_t uxSendCount = ipconfigMAX_ARP_RETRANSMISSIONS;
    uint32_t ulIPAddressCopy = ulIPAddress;

    /* The IP-task is not supposed to call this function. */
    configASSERT( xIsCallingFromIPTask() == pdFALSE );

    xLookupResult = eARPGetCacheEntry( &( ulIPAddressCopy ), &( xMACAddress ), &( pxEndPoint ) );

    if( xLookupResult == eARPCacheMiss )
    {
        const TickType_t uxSleepTime = pdMS_TO_TICKS( 250U );

        /* We might use ipconfigMAX_ARP_RETRANSMISSIONS here. */
        vTaskSetTimeOutState( &xTimeOut );

        while( uxSendCount > 0U )
        {
            FreeRTOS_OutputARPRequest( ulIPAddressCopy );

            vTaskDelay( uxSleepTime );

            xLookupResult = eARPGetCacheEntry( &( ulIPAddressCopy ), &( xMACAddress ), &( pxEndPoint ) );

            if( ( xTaskCheckForTimeOut( &( xTimeOut ), &( uxTicksToWait ) ) == pdTRUE ) ||
                ( xLookupResult != eARPCacheMiss ) )
            {
                break;
            }

            /* Decrement the count. */
            uxSendCount--;
        }
    }

    if( xLookupResult == eARPCacheHit )
    {
        xResult = 0;
    }

    return xResult;
}
/*-----------------------------------------------------------*/

/**
 * @brief Generate an ARP request packet by copying various constant details to
 *        the buffer.
 *
 * @param[in,out] pxNetworkBuffer: Pointer to the buffer which has to be filled with
 *                             the ARP request packet details.
 */
void vARPGenerateRequestPacket( NetworkBufferDescriptor_t * const pxNetworkBuffer )
{
/* Part of the Ethernet and ARP headers are always constant when sending an IPv4
 * ARP packet.  This array defines the constant parts, allowing this part of the
 * packet to be filled in using a simple memcpy() instead of individual writes. */
    static const uint8_t xDefaultPartARPPacketHeader[] =
    {
        0xff, 0xff, 0xff, 0xff, 0xff, 0xff, /* Ethernet destination address. */
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* Ethernet source address. */
        0x08, 0x06,                         /* Ethernet frame type (ipARP_FRAME_TYPE). */
        0x00, 0x01,                         /* usHardwareType (ipARP_HARDWARE_TYPE_ETHERNET). */
        0x08, 0x00,                         /* usProtocolType. */
        ipMAC_ADDRESS_LENGTH_BYTES,         /* ucHardwareAddressLength. */
        ipIP_ADDRESS_LENGTH_BYTES,          /* ucProtocolAddressLength. */
        0x00, 0x01,                         /* usOperation (ipARP_REQUEST). */
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* xSenderHardwareAddress. */
        0x00, 0x00, 0x00, 0x00,             /* ulSenderProtocolAddress. */
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00  /* xTargetHardwareAddress. */
    };

    ARPPacket_t * pxARPPacket;

/* memcpy() helper variables for MISRA Rule 21.15 compliance*/
    const void * pvCopySource;
    void * pvCopyDest;

    /* Buffer allocation ensures that buffers always have space
     * for an ARP packet. See buffer allocation implementations 1
     * and 2 under portable/BufferManagement. */
    configASSERT( pxNetworkBuffer != NULL );
    configASSERT( pxNetworkBuffer->xDataLength >= sizeof( ARPPacket_t ) );
    configASSERT( pxNetworkBuffer->pxEndPoint != NULL );

    /* MISRA Ref 11.3.1 [Misaligned access] */
/* More details at: https://github.com/FreeRTOS/FreeRTOS-Plus-TCP/blob/main/MISRA.md#rule-113 */
    /* coverity[misra_c_2012_rule_11_3_violation] */
    pxARPPacket = ( ( ARPPacket_t * ) pxNetworkBuffer->pucEthernetBuffer );

    /* memcpy the const part of the header information into the correct
     * location in the packet.  This copies:
     *  xEthernetHeader.ulDestinationAddress
     *  xEthernetHeader.usFrameType;
     *  xARPHeader.usHardwareType;
     *  xARPHeader.usProtocolType;
     *  xARPHeader.ucHardwareAddressLength;
     *  xARPHeader.ucProtocolAddressLength;
     *  xARPHeader.usOperation;
     *  xARPHeader.xTargetHardwareAddress;
     */

    /*
     * Use helper variables for memcpy() to remain
     * compliant with MISRA Rule 21.15.  These should be
     * optimized away.
     */
    pvCopySource = xDefaultPartARPPacketHeader;
    pvCopyDest = pxARPPacket;
    ( void ) memcpy( pvCopyDest, pvCopySource, sizeof( xDefaultPartARPPacketHeader ) );

    pvCopySource = pxNetworkBuffer->pxEndPoint->xMACAddress.ucBytes;
    pvCopyDest = pxARPPacket->xEthernetHeader.xSourceAddress.ucBytes;
    ( void ) memcpy( pvCopyDest, pvCopySource, ipMAC_ADDRESS_LENGTH_BYTES );

    pvCopySource = pxNetworkBuffer->pxEndPoint->xMACAddress.ucBytes;
    pvCopyDest = pxARPPacket->xARPHeader.xSenderHardwareAddress.ucBytes;
    ( void ) memcpy( pvCopyDest, pvCopySource, ipMAC_ADDRESS_LENGTH_BYTES );

    pvCopySource = &( pxNetworkBuffer->pxEndPoint->ipv4_settings.ulIPAddress );
    pvCopyDest = pxARPPacket->xARPHeader.ucSenderProtocolAddress;
    ( void ) memcpy( pvCopyDest, pvCopySource, sizeof( pxARPPacket->xARPHeader.ucSenderProtocolAddress ) );
    pxARPPacket->xARPHeader.ulTargetProtocolAddress = pxNetworkBuffer->xIPAddress.ulIP_IPv4;

    pxNetworkBuffer->xDataLength = sizeof( ARPPacket_t );

    iptraceCREATING_ARP_REQUEST( pxNetworkBuffer->xIPAddress.ulIP_IPv4 );
}
/*-----------------------------------------------------------*/

/**
 * @brief A call to this function will clear the ARP cache.
 * @param[in] pxEndPoint: only clean entries with this end-point, or when NULL,
 *                        clear the entire ARP cache.
 */
void FreeRTOS_ClearARP( const struct xNetworkEndPoint * pxEndPoint )
{
    if( pxEndPoint != NULL )
    {
        BaseType_t x;

        for( x = 0; x < ipconfigARP_CACHE_ENTRIES; x++ )
        {
            if( xARPCache[ x ].pxEndPoint == pxEndPoint )
            {
                ( void ) memset( &( xARPCache[ x ] ), 0, sizeof( ARPCacheRow_t ) );
            }
        }
    }
    else
    {
        ( void ) memset( xARPCache, 0, sizeof( xARPCache ) );
    }
}
/*-----------------------------------------------------------*/

#if 1

/**
 * @brief  This function will check if the target IP-address belongs to this device.
 *         If so, the packet will be passed to the IP-stack, who will answer it.
 *         The function is to be called within the function xNetworkInterfaceOutput().
 *
 * @param[in] pxDescriptor: The network buffer which is to be checked for loop-back.
 * @param[in] bReleaseAfterSend: pdTRUE: Driver is allowed to transfer ownership of descriptor.
 *                              pdFALSE: Driver is not allowed to take ownership of descriptor,
 *                                       make a copy of it.
 *
 * @return pdTRUE/pdFALSE: There is/isn't a loopback address in the packet.
 */
    BaseType_t xCheckLoopback( NetworkBufferDescriptor_t * const pxDescriptor,
                               BaseType_t bReleaseAfterSend )
    {
        BaseType_t xResult = pdFALSE;
        NetworkBufferDescriptor_t * pxUseDescriptor = pxDescriptor;

        /* MISRA Ref 11.3.1 [Misaligned access] */
/* More details at: https://github.com/FreeRTOS/FreeRTOS-Plus-TCP/blob/main/MISRA.md#rule-113 */
        /* coverity[misra_c_2012_rule_11_3_violation] */
        const IPPacket_t * pxIPPacket = ( ( IPPacket_t * ) pxUseDescriptor->pucEthernetBuffer );

        if( pxIPPacket->xEthernetHeader.usFrameType == ipIPv4_FRAME_TYPE )
        {
            NetworkEndPoint_t * pxEndPoint;

            pxEndPoint = FreeRTOS_FindEndPointOnMAC( &( pxIPPacket->xEthernetHeader.xDestinationAddress ), NULL );

            if( ( pxEndPoint != NULL ) &&
                ( memcmp( pxIPPacket->xEthernetHeader.xDestinationAddress.ucBytes, pxEndPoint->xMACAddress.ucBytes, ipMAC_ADDRESS_LENGTH_BYTES ) == 0 ) )
            {
                xResult = pdTRUE;

                if( bReleaseAfterSend == pdFALSE )
                {
                    /* Driver is not allowed to transfer the ownership
                     * of descriptor,  so make a copy of it */
                    pxUseDescriptor =
                        pxDuplicateNetworkBufferWithDescriptor( pxDescriptor, pxDescriptor->xDataLength );
                }

                if( pxUseDescriptor != NULL )
                {
                    IPStackEvent_t xRxEvent;

                    pxUseDescriptor->pxInterface = pxEndPoint->pxNetworkInterface;
                    pxUseDescriptor->pxEndPoint = pxEndPoint;

                    xRxEvent.eEventType = eNetworkRxEvent;
                    xRxEvent.pvData = pxUseDescriptor;

                    if( xSendEventStructToIPTask( &xRxEvent, 0U ) != pdTRUE )
                    {
                        vReleaseNetworkBufferAndDescriptor( pxUseDescriptor );
                        iptraceETHERNET_RX_EVENT_LOST();
                        FreeRTOS_printf( ( "prvEMACRxPoll: Can not queue return packet!\n" ) );
                    }
                }
            }
        }

        return xResult;
    }

#endif /* 0 */
/*-----------------------------------------------------------*/

#if ( ipconfigHAS_PRINTF != 0 ) || ( ipconfigHAS_DEBUG_PRINTF != 0 )

    void FreeRTOS_PrintARPCache( void )
    {
        BaseType_t x, xCount = 0;

        /* Loop through each entry in the ARP cache. */
        for( x = 0; x < ipconfigARP_CACHE_ENTRIES; x++ )
        {
            if( ( xARPCache[ x ].ulIPAddress != 0U ) && ( xARPCache[ x ].ucAge > ( uint8_t ) 0U ) )
            {
                /* See if the MAC-address also matches, and we're all happy */
                FreeRTOS_printf( ( "ARP %2d: %3u - %16xip : %02x:%02x:%02x : %02x:%02x:%02x\n",
                                   ( int ) x,
                                   xARPCache[ x ].ucAge,
                                   ( unsigned ) FreeRTOS_ntohl( xARPCache[ x ].ulIPAddress ),
                                   xARPCache[ x ].xMACAddress.ucBytes[ 0 ],
                                   xARPCache[ x ].xMACAddress.ucBytes[ 1 ],
                                   xARPCache[ x ].xMACAddress.ucBytes[ 2 ],
                                   xARPCache[ x ].xMACAddress.ucBytes[ 3 ],
                                   xARPCache[ x ].xMACAddress.ucBytes[ 4 ],
                                   xARPCache[ x ].xMACAddress.ucBytes[ 5 ] ) );
                xCount++;
            }
        }

        FreeRTOS_printf( ( "Arp has %ld entries\n", xCount ) );
    }
#endif /* ( ipconfigHAS_PRINTF != 0 ) || ( ipconfigHAS_DEBUG_PRINTF != 0 ) */