esp-idf/components/lwip/Kconfig

menu "LWIP"

config L2_TO_L3_COPY
    bool "Enable copy between Layer2 and Layer3 packets"
    default n
    help
        If this feature is enabled, all traffic from layer2(WIFI Driver) will be
        copied to a new buffer before sending it to layer3(LWIP stack), freeing
        the layer2 buffer.
        Please be notified that the total layer2 receiving buffer is fixed and 
        ESP32 currently supports 25 layer2 receiving buffer, when layer2 buffer 
        runs out of memory, then the incoming packets will be dropped in hardware. 
        The layer3 buffer is allocated from the heap, so the total layer3 receiving
        buffer depends on the available heap size, when heap runs out of memory,  
        no copy will be sent to layer3 and packet will be dropped in layer2. 
        Please make sure you fully understand the impact of this feature before 
        enabling it.

config LWIP_IRAM_OPTIMIZATION
    bool "Enable LWIP IRAM optimization"
    default n
    help
        If this feature is enabled, some functions relating to RX/TX in LWIP will be
        put into IRAM, it can improve UDP/TCP throughput by >10% for single core mode,
        it doesn't help too much for dual core mode. On the other hand, it needs about
        10KB IRAM for these optimizations.

        If this feature is disabled, all lwip functions will be put into FLASH.

config LWIP_MAX_SOCKETS
    int "Max number of open sockets"
    range 1 16
    default 10
    help
        Sockets take up a certain amount of memory, and allowing fewer
        sockets to be open at the same time conserves memory. Specify
        the maximum amount of sockets here. The valid value is from 1
        to 16.

config USE_ONLY_LWIP_SELECT
    bool "Support LWIP socket select() only"
    default n
    help
        The virtual filesystem layer of select() redirects sockets to
        lwip_select() and non-socket file descriptors to their respective driver
        implementations. If this option is enabled then all calls of select()
        will be redirected to lwip_select(), therefore, select can be used
        for sockets only.

config LWIP_SO_REUSE
    bool "Enable SO_REUSEADDR option"
    default y
    help
        Enabling this option allows binding to a port which remains in
        TIME_WAIT.

config LWIP_SO_REUSE_RXTOALL
    bool "SO_REUSEADDR copies broadcast/multicast to all matches"
    depends on LWIP_SO_REUSE
    default y
    help
        Enabling this option means that any incoming broadcast or multicast
        packet will be copied to all of the local sockets that it matches
        (may be more than one if SO_REUSEADDR is set on the socket.)

        This increases memory overhead as the packets need to be copied,
        however they are only copied per matching socket. You can safely
        disable it if you don't plan to receive broadcast or multicast
        traffic on more than one socket at a time.

config LWIP_SO_RCVBUF
    bool "Enable SO_RCVBUF option"
    default n
    help
        Enabling this option allows checking for available data on a netconn.

config LWIP_DHCP_MAX_NTP_SERVERS
    int "Maximum number of NTP servers"
    default 1
    range 1 16
    help
        Set maximum number of NTP servers used by LwIP SNTP module.
        First argument of sntp_setserver/sntp_setservername functions
        is limited to this value.

config LWIP_IP_FRAG
    bool "Enable fragment outgoing IP packets"
    default n
    help
        Enabling this option allows fragmenting outgoing IP packets if their size
        exceeds MTU.

config LWIP_IP_REASSEMBLY
    bool "Enable reassembly incoming fragmented IP packets"
    default n
    help
        Enabling this option allows reassemblying incoming fragmented IP packets.

config LWIP_STATS
    bool "Enable LWIP statistics"
    default n
    help
        Enabling this option allows LWIP statistics

config LWIP_ETHARP_TRUST_IP_MAC
    bool "Enable LWIP ARP trust"
    default n
    help
        Enabling this option allows ARP table to be updated.

        If this option is enabled, the incoming IP packets cause the ARP table to be
        updated with the source MAC and IP addresses supplied in the packet.
        You may want to disable this if you do not trust LAN peers to have the
        correct addresses, or as a limited approach to attempt to handle
        spoofing. If disabled, lwIP will need to make a new ARP request if
        the peer is not already in the ARP table, adding a little latency.
        The peer *is* in the ARP table if it requested our address before.
        Also notice that this slows down input processing of every IP packet!

        There are two known issues in real application if this feature is enabled:
         - The LAN peer may have bug to update the ARP table after the ARP entry is aged out.
           If the ARP entry on the LAN peer is aged out but failed to be updated, all IP packets
           sent from LWIP to the LAN peer will be dropped by LAN peer.
         - The LAN peer may not be trustful, the LAN peer may send IP packets to LWIP with 
           two different MACs, but the same IP address. If this happens, the LWIP has problem
           to receive IP packets from LAN peer.

        So the recommendation is to disable this option. 
        Here the LAN peer means the other side to which the ESP station or soft-AP is connected.

config TCPIP_RECVMBOX_SIZE
    int "TCPIP task receive mail box size"
    default 32
    range 6 64
    help
        Set TCPIP task receive mail box size. Generally bigger value means higher throughput
        but more memory. The value should be bigger than UDP/TCP mail box size.

config LWIP_DHCP_DOES_ARP_CHECK
    bool "DHCP: Perform ARP check on any offered address"
    default y
    help
        Enabling this option performs a check (via ARP request) if the offered IP address
        is not already in use by another host on the network.

menu "DHCP server"

config LWIP_DHCPS_LEASE_UNIT
    int "Multiplier for lease time, in seconds"
    range 1 3600
    default 60
    help
        The DHCP server is calculating lease time multiplying the sent 
        and received times by this number of seconds per unit. 
        The default is 60, that equals one minute.

config LWIP_DHCPS_MAX_STATION_NUM
    int "Maximum number of stations"
    range 1 64
    default 8
    help
        The maximum number of DHCP clients that are connected to the server.
        After this number is exceeded, DHCP server removes of the oldest device
        from it's address pool, without notification.

endmenu # DHCPS

menuconfig LWIP_AUTOIP
    bool "Enable IPV4 Link-Local Addressing (AUTOIP)"
    default n
    help
        Enabling this option allows the device to self-assign an address
        in the 169.256/16 range if none is assigned statically or via DHCP.

        See RFC 3927.

config LWIP_AUTOIP_TRIES
    int "DHCP Probes before self-assigning IPv4 LL address"
    range 1 100
    default 2
    depends on LWIP_AUTOIP
    help
        DHCP client will send this many probes before self-assigning a
        link local address.

        From LWIP help: "This can be set as low as 1 to get an AutoIP
        address very quickly, but you should be prepared to handle a
        changing IP address when DHCP overrides AutoIP." (In the case of
        ESP-IDF, this means multiple SYSTEM_EVENT_STA_GOT_IP events.)

config LWIP_AUTOIP_MAX_CONFLICTS
    int "Max IP conflicts before rate limiting"
    range 1 100
    default 9
    depends on LWIP_AUTOIP
    help
        If the AUTOIP functionality detects this many IP conflicts while
        self-assigning an address, it will go into a rate limited mode.

config LWIP_AUTOIP_RATE_LIMIT_INTERVAL
    int "Rate limited interval (seconds)"
    range 5 120
    default 20
    depends on LWIP_AUTOIP
    help
        If rate limiting self-assignment requests, wait this long between
        each request.

menuconfig LWIP_NETIF_LOOPBACK
    bool "Support per-interface loopback"
    default y
    help
        Enabling this option means that if a packet is sent with a destination
        address equal to the interface's own IP address, it will "loop back" and
        be received by this interface.

config LWIP_LOOPBACK_MAX_PBUFS
    int "Max queued loopback packets per interface"
    range 0 16
    default 8
    depends on LWIP_NETIF_LOOPBACK
    help
         Configure the maximum number of packets which can be queued for
         loopback on a given interface. Reducing this number may cause packets
         to be dropped, but will avoid filling memory with queued packet data.

menu "TCP"

config LWIP_MAX_ACTIVE_TCP
    int "Maximum active TCP Connections"
    range 1 1024
    default 16
    help
        The maximum number of simultaneously active TCP
        connections. The practical maximum limit is
        determined by available heap memory at runtime.

        Changing this value by itself does not substantially
        change the memory usage of LWIP, except for preventing
        new TCP connections after the limit is reached.

config LWIP_MAX_LISTENING_TCP
    int "Maximum listening TCP Connections"
    range 1 1024
    default 16
    help
        The maximum number of simultaneously listening TCP
        connections. The practical maximum limit is
        determined by available heap memory at runtime.

        Changing this value by itself does not substantially
        change the memory usage of LWIP, except for preventing
        new listening TCP connections after the limit is reached.


config TCP_MAXRTX
    int "Maximum number of retransmissions of data segments"
    default 12
    range 3 12
    help
        Set maximum number of retransmissions of data segments.

config TCP_SYNMAXRTX
    int "Maximum number of retransmissions of SYN segments"
    default 6
    range 3 12
    help
        Set maximum number of retransmissions of SYN segments.

config TCP_MSS
    int "Maximum Segment Size (MSS)"
    default 1436
    range 1220 1436
    help
        Set maximum segment size for TCP transmission.

        Can be set lower to save RAM, the default value 1436 will give best throughput.

config TCP_MSL
    int "Maximum segment lifetime (MSL)"
    default 60000
    help
        Set maximum segment lifetime in in milliseconds.

config TCP_SND_BUF_DEFAULT
    int "Default send buffer size"
    default 5744  # 4 * default MSS
    range 2440 65535
    help
        Set default send buffer size for new TCP sockets.

        Per-socket send buffer size can be changed at runtime
        with lwip_setsockopt(s, TCP_SNDBUF, ...).

        This value must be at least 2x the MSS size, and the default
        is 4x the default MSS size.

        Setting a smaller default SNDBUF size can save some RAM, but
        will decrease performance.

config TCP_WND_DEFAULT
    int "Default receive window size"
    default 5744 # 4 * default MSS
    range 2440 65535
    help
        Set default TCP receive window size for new TCP sockets.

        Per-socket receive window size can be changed at runtime
        with lwip_setsockopt(s, TCP_WINDOW, ...).

        Setting a smaller default receive window size can save some RAM,
        but will significantly decrease performance.

config TCP_RECVMBOX_SIZE
    int "Default TCP receive mail box size"
    default 6
    range 6 64
    help
        Set TCP receive mail box size. Generally bigger value means higher throughput
        but more memory. The recommended value is: TCP_WND_DEFAULT/TCP_MSS + 2, e.g. if 
        TCP_WND_DEFAULT=14360, TCP_MSS=1436, then the recommended receive mail box size is 
        (14360/1436 + 2) = 12.

        TCP receive mail box is a per socket mail box, when the application receives packets
        from TCP socket, LWIP core firstly posts the packets to TCP receive mail box and the 
        application then fetches the packets from mail box. It means LWIP can caches maximum 
        TCP_RECCVMBOX_SIZE packets for each TCP socket, so the maximum possible cached TCP packets
        for all TCP sockets is TCP_RECCVMBOX_SIZE multiples the maximum TCP socket number. In other
        words, the bigger TCP_RECVMBOX_SIZE means more memory.
        On the other hand, if the receiv mail box is too small, the mail box may be full. If the 
        mail box is full, the LWIP drops the packets. So generally we need to make sure the TCP
        receive mail box is big enough to avoid packet drop between LWIP core and application.

config TCP_QUEUE_OOSEQ
    bool "Queue incoming out-of-order segments"
    default y
    help
        Queue incoming out-of-order segments for later use.

        Disable this option to save some RAM during TCP sessions, at the expense
        of increased retransmissions if segments arrive out of order.

config ESP_TCP_KEEP_CONNECTION_WHEN_IP_CHANGES
    bool "Keep TCP connections when IP changed"
    default n
    help
        This option is enabled when the following scenario happen:
        network dropped and reconnected, IP changes is like: 192.168.0.2->0.0.0.0->192.168.0.2
        
        Disable this option to keep consistent with the original LWIP code behavior.


choice TCP_OVERSIZE
    prompt "Pre-allocate transmit PBUF size"
    default TCP_OVERSIZE_MSS
    help
        Allows enabling "oversize" allocation of TCP transmission pbufs ahead of time,
        which can reduce the length of pbuf chains used for transmission.

        This will not make a difference to sockets where Nagle's algorithm
        is disabled.

        Default value of MSS is fine for most applications, 25% MSS may save
        some RAM when only transmitting small amounts of data. Disabled will
        have worst performance and fragmentation characteristics, but uses
        least RAM overall.

config TCP_OVERSIZE_MSS
     bool "MSS"
config TCP_OVERSIZE_QUARTER_MSS
     bool "25% MSS"
config TCP_OVERSIZE_DISABLE
     bool "Disabled"

endchoice

endmenu # TCP

menu "UDP"

config LWIP_MAX_UDP_PCBS
    int "Maximum active UDP control blocks"
    range 1 1024
    default 16
    help
        The maximum number of active UDP "connections" (ie
        UDP sockets sending/receiving data).
        The practical maximum limit is determined by available
        heap memory at runtime.

config UDP_RECVMBOX_SIZE
    int "Default UDP receive mail box size"
    default 6
    range 6 64
    help
        Set UDP receive mail box size. The recommended value is 6.

        UDP receive mail box is a per socket mail box, when the application receives packets 
        from UDP socket, LWIP core firstly posts the packets to UDP receive mail box and the
        application then fetches the packets from mail box. It means LWIP can caches maximum
        UDP_RECCVMBOX_SIZE packets for each UDP socket, so the maximum possible cached UDP packets 
        for all UDP sockets is UDP_RECCVMBOX_SIZE multiples the maximum UDP socket number. In other
        words, the bigger UDP_RECVMBOX_SIZE means more memory.
        On the other hand, if the receiv mail box is too small, the mail box may be full. If the
        mail box is full, the LWIP drops the packets. So generally we need to make sure the UDP
        receive mail box is big enough to avoid packet drop between LWIP core and application.

endmenu # UDP

config TCPIP_TASK_STACK_SIZE
    int "TCP/IP Task Stack Size"
    default 2048
    # for high log levels, tcpip_adapter API calls can end up
    # a few calls deep and logging there can trigger a stack overflow
    range 2048 65536 if LOG_DEFAULT_LEVEL < 4
    range 2560 65536 if LOG_DEFAULT_LEVEL >= 4
    help
       Configure TCP/IP task stack size, used by LWIP to process multi-threaded TCP/IP operations.
       Setting this stack too small will result in stack overflow crashes.

menuconfig PPP_SUPPORT
    bool "Enable PPP support (new/experimental)"
    default n
    help
        Enable PPP stack. Now only PPP over serial is possible.

        PPP over serial support is experimental and unsupported.

config PPP_PAP_SUPPORT
   bool "Enable PAP support"
   depends on PPP_SUPPORT
   default n
   help
       Enable Password Authentication Protocol (PAP) support

config PPP_CHAP_SUPPORT
   bool "Enable CHAP support"
   depends on PPP_SUPPORT
   default n
   help
       Enable Challenge Handshake Authentication Protocol (CHAP) support

config PPP_MSCHAP_SUPPORT
   bool "Enable MSCHAP support"
   depends on PPP_SUPPORT
   default n
   help
       Enable Microsoft version of the Challenge-Handshake Authentication Protocol (MSCHAP) support

config PPP_MPPE_SUPPORT
   bool "Enable MPPE support"
   depends on PPP_SUPPORT
   default n
   help
       Enable Microsoft Point-to-Point Encryption (MPPE) support

config PPP_DEBUG_ON
   bool "Enable PPP debug log output"
   depends on PPP_SUPPORT
   default n
   help
       Enable PPP debug log output

menu "ICMP"

config LWIP_MULTICAST_PING
   bool "Respond to multicast pings"
   default n

config LWIP_BROADCAST_PING
   bool "Respond to broadcast pings"
   default n

endmenu # ICMP

menu "LWIP RAW API"

config LWIP_MAX_RAW_PCBS
    int "Maximum LWIP RAW PCBs"
    range 1 1024
    default 16
    help
        The maximum number of simultaneously active LWIP
        RAW protocol control blocks. The practical maximum
        limit is determined by available heap memory at runtime.

endmenu  # LWIP RAW API

endmenu