Information Technology Reference
In-Depth Information
The fields are
•
SSS…SSS, security (16 bits) - These specify one of 16 levels of security, such as
00000000 00000000 - Unclassified
11110001 00110101 - Confidential
01111000 10011010 - EFTO
10111100 01001101 - MMMM
01011110 00100110 - PROG
10101111 00010011 - Restricted
11010111 10001000 - Secret
01101011 11000101 - Top Secret
00110101 11100010 - Reserved
10011010 11110001 - Reserved
01001101 01111000 - Reserved
00100100 10111101 - Reserved
00010011 01011110 - Reserved
10001001 10101111 - Reserved
11000100 11010110 - Reserved
11100010 01101011 - Reserved
•
CCC…CCC, compartments (16 bits) - When this field contains all zero values then the
transmitted information is not compartmented, other values can be obtained from the
Defense Intelligence Agency.
•
HHH…HHH, handling restrictions (16 bits) - This field is defined in the Defense In-
telligence Agency Manual DIAM 65-19.
•
TCC, transmission control code (24 bits) - This field allows the segregation of traffic
and to define controlled communities of interest among subscribers (available from HQ
DCA Code 530). Must be copied on fragmentation.
Loose source and record route (Type = 131)
Loose source and record route (LSRR) allows for the source of an internet datagram to sup-
ply routing information to be used by the gateways in forwarding the datagram to the desti-
nation. It can also be used to record routing information.
When routing the source host adds the IP addresses of the route to the route data, and
each gateway routes the datagram using the recorded route, and not with its own internal
routing table. This allows datagrams to take alternative routes through the Internet. Its format
is
+--------+--------+--------+---------...--------+
|10000011| Length | Pointer| Route data |
+--------+--------+--------+---------...--------+
where
•
Length - this is a single byte which contains the number of bytes in the option field.
•
Pointer - this is a pointer, which is relative to this option, into the route data which indi-
cates the byte which begins the next source address to be processed. The smallest value
is 4.
•
Route data - this is constructed with a number of internet addresses, each of 4 bytes in
length. If the pointer is greater than the length, the source route is empty (and the re-
corded route full) and the routing is to be based on the destination address field.
When reaching the address in the destination address field, and when the pointer is not
greater than the length in the route data, then the next address in the source route data re-
places the address in the destination field. The pointer is also incremented by 4, to point to
