The messageType field indicates what type of message is being relayed, and
must conform to the following enumeration
.TS
allbox tab(:);
cb cb cb cb cb
c l l l c.
messageType:Name:On Bootstrap:On Realtime:Version
0x00:Invalid:Yes:Yes:1+
0x01:Not_A_Type:Yes:Yes:1+
0x02:Keepalive:No:Yes:1+
0x03:Publish:No:Yes:1+
0x04:Confirm_Req:No:Yes:1+
0x05:Confirm_Ack:No:Yes:1+
0x06:Bulk_Pull:Yes:No:1+
0x07:Bulk_Push:Yes:No:1+
0x08:Frontier_Req:Yes:No:1+
0x09:Bulk_Pull_Blocks:Yes:No:Deprecated
0x0A:Node_ID_Handshake:Yes:No:12+
0x0B:Bulk_Pull_Account:Yes:No:12+
.TE

.TP
.B Extensions
The following message types have extension bits used as flags:
.IR Node_ID_Handshake ", " Bulk_Pull .

The following message types encode a block type in the extension bits:
.IR Publish ", " Confirm_Req ", and " Confirm_Ack .
The block type is encoded in the lower 4 bits of the first byte of the
extensions field (i.e., (extensions & 0x0f00 >> 8)).

.SS Payload
Following the message header comes the payload for the particular message
type.

.TP
.B Invalid
TODOC

.TP
.B Not_A_Type
TODOC

.TP
.B Keepalive
The
.I Keepalive
message serves as an introduction and beaconing mechanism for
the Nano real-time network.
The Keepalive message requires exactly 8 IPv6 address and port number
tuples to be sent as its payload.  The IPv6 addresses are each 128-bits
(16-bytes) long and the port numbers are 16-bit integers sent in little endian
byte order.  The payload for the Keepalive message type is 144 bytes in size.

.TP
.B Publish
The
.I Publish
message serves as a mechanism to introduce new blocks into the
Nano real-time network.  The block type is encoded in the
.I Extensions
field as described above.  The payload is the contents of the block.

.TP
.B Confirm_Req
The
.I Confirm_Req
message requests that all online representatives "vote" on a block.
The block type is encoded in the
.I Extensions
field as described above.  The payload is the contents of the block
to be voted on.

.TP
.B Confirm_Ack
The
.I Confirm_Ack
message is sent in response to either a new block being observed
by a representative or in response to an explicit
.IR Confirm_Req .
The block type is encoded in the
.I Extensions
field as described above.
If the block type is specified as
.I Not_A_Block
then the payload is a sequence of hashes.  Due to IPv4 fragment
size limits this typically does not exceed 12 hashes.  If the
block type is something other than
.I Not_A_Block
then the payload is the contents of the block that is being
voted on.

.TP
.B Bulk_Pull
The Bulk_Pull message is used to pull the entire chain for an account, down to
its beginning or to a given block.  It takes 2 arguments, both of them 256-bit.
The first argument is the account, so its 256-bit public key should be encoded
as binary in big-endian notation.  The second argument is the block hash to