TCP/IP - Computer Busses - page 369

• Length. - is a single byte which contains the number of bytes in the option field (maxi-

mum is 40).

• Pointer - this is a pointer, which is relative to this option, into the route data which indi-

cates the byte at which the next timestamp should be added to. The smallest value is 5.

• Overflow (Ov) - this has four bits and holds the number of IP modules that cannot regis-

ter timestamps due to lack of space.

• Flag (Flg) - this has four bits and defines the format of the timestamp. Valid values are:

0 - Store only the time stamps as 32-bit words.
1 - Store IP address followed by a time stamp.
3 - In this mode the IP addresses are specified in a table. A gateway only adds its time-
stamp if its IP address is in this table.

• Timestamp - this is a 32-bit value for the number of milliseconds since midnight UT

(universal time). If this is not possible then it is any time, as long as the high-order bit of
the timestamp is set to a 1 to indicate that it is non-standard time.

The originating host must reserve enough area for the total number of timestamps, as the size
of this option does not change as it transverses over the Internet. If there is a problem adding
the address then an ICMP parameter problem can be sent back to the source host. Initially the
contents of the timestamp data area is either zero, or has IP addresses with zero time stamps.
The timestamp area is full when the pointer is greater than the length.
It is not copied on fragmentation, and goes in the first fragment only. Also, it occurs, at
the most once in a datagram.

Stream identifier (type =136)
This option allows for a 16-bit SATNET stream identifier to be carried through networks that
do not support the stream concept. Its format is

+--------+--------+--------+--------+
|10001000|00000010| Stream ID |
+--------+--------+--------+--------+
23.16.3 Ethernet multicast/broadcast addresses
The following is a list of typical Ethernet multicast addresses:

Ethernet address Type field Usage
01-00-5E-00-00-00 0800 Internet multicast (RFC-1112)
01-80-C2-00-00-00 0802 Spanning tree (for bridges)
09-00-09-00-00-01 8005 HP probe
09-00-09-00-00-04 8005 HP DTC
09-00-1E-00-00-00 8019 Apollo DOMAIN
09-00-2B-00-00-03 8038 DEC lanbridge traffic monitor (LTM)
09-00-4E-00-00-02 8137 Novell IPX
CF-00-00-00-00-00 9000 Ethernet configuration test protocol

The following is a list of typical Ethernet broadcast addresses:

Ethernet address Type field Usage

FF-FF-FF-FF-FF-FF 0600 XNS packets, hello or gateway search.