NAME

     netdump — protocol for transmitting kernel dumps to a remote server

SYNOPSIS

     To compile netdump client support into the kernel, place the following line in your kernel configuration
     file:

           options NETDUMP

DESCRIPTION

     netdump is a UDP-based protocol for transmitting kernel dumps to a remote host.  A netdump client is a
     panicking kernel, and a netdump server is a host running the netdump daemon, available in ports as
     ports/ftp/netdumpd.  netdump clients are configured using the dumpon(8) utility.

     netdump client messages consist of a fixed-size header followed by a variable-sized payload.  The header
     contains the message type, a sequence number, the offset of the payload data in the kernel dump, and the
     length of the payload data (not including the header).  The message types are HERALD, FINISHED, KDH,
     VMCORE, and EKCD_KEY.  netdump server messages have a fixed size and contain only the sequence number of
     the client message.  These messages indicate that the server has successfully processed the client message
     with the corresponding sequence number.  All client messages are acknowledged this way.  Server messages
     are always sent to port 20024 of the client.

     To initiate a netdump, the client sends a HERALD message to the server at port 20023.  The client may
     include a relative path in its payload, in which case the netdump server should attempt to save the dump at
     that path relative to its configured dump directory.  The server will acknowledge the HERALD using a random
     source port, and the client must send all subsequent messages to that port.

     The KDH, VMCORE, and EKCD_KEY message payloads contain the kernel dump header, dump contents, and dump
     encryption key respectively.  The offset in the message header should be treated as a seek offset in the
     corresponding file.  There are no ordering requirements for these messages.

     A netdump is completed by sending the FINISHED message to the server.

     The following network drivers support netdump: alc(4), bge(4), bnxt(4), bxe(4), cxgb(4), em(4), igb(4),
     ix(4), ixl(4), mlx4en(4), mlx5en(4), re(4), vtnet(4).

SYSCTL VARIABLES

     The following variables are available as both sysctl(8) variables and loader(8) variables:

     net.netdump.debug
             Control debug message verbosity.  Debug messages are disabled by default, but are useful when
             troubleshooting or when developing driver support.

     net.netdump.path
             Specify a path relative to the server's dump directory in which to store the dump.  For example, if
             the netdump server is configured to store dumps in /var/crash, a path of “foo” will cause the
             server to attempt to store dumps from the client in /var/crash/foo.  The server will not
             automatically create the relative directory.

     net.netdump.polls
             The client will poll the configured network interface while waiting for acknowledgements.  This
             parameter controls the maximum number of poll attempts before giving up, which typically results in
             a re-transmit.  Each poll attempt takes 0.5ms.

     net.netdump.retries
             The number of times the client will re-transmit a packet before aborting a dump due to a lack of
             acknowledgement.  The default may be too small in environments with lots of packet loss.

     net.netdump.arp_retries
             The number of times the client will attempt to learn the MAC address of the configured gateway or
             server before giving up and aborting the dump.

SEE ALSO

     decryptcore(8), dumpon(8), savecore(8)

HISTORY

     netdump client support first appeared in FreeBSD 12.0.

BUGS

     Only IPv4 is supported.

     netdump may only be used after the kernel has panicked.