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Route
Click on the red underlined text to get to the source
... sender of the datagram and
reduced at the points along the route where it is processed. If the
time to live reaches zero before the internet ...
... name indicates what we seek. An address indicates where it is. A
route indicates how to get there. The internet protocol deals
primarily with addresses ...
... datagram based on information
supplied by the source.
0 7 var. Record Route. Used to trace the route an
...
... datagram.
Loose Source and Record Route
+--------+--------+--------+---------//--------+
...
...
+--------+--------+--------+---------//--------+
|10000011| length | pointer| route data |
+--------+--------+--------+---------//--------+
Type=131
...
... Type=131
The loose source and record route (LSRR) option provides a means
for the source of an internet ...
... is the option length which includes the option type code and the
length octet, the pointer octet, and length-3 octets of route
data. The third octet is the pointer into the route data
...
... length octet, the pointer octet, and length-3 octets of route
data. The third octet is the pointer into the route data
indicating the octet which begins the next source address to be
...
... smallest legal value for the pointer is 4.
A route data is composed of a series of internet addresses.
Each internet address ...
... 32 bits or 4 octets. If the pointer is
greater than the length, the source route is empty (and the
recorded route full) and the routing ...
... greater than the length, the source route is empty (and the
recorded route full) and the routing is to be based on the
destination address field ...
... the pointer is not greater than the length, the next address in
the source route replaces the address in the destination address
field, and the recorded route ...
... source route replaces the address in the destination address
field, and the recorded route address replaces the source
address just used, and pointer is increased by four.
...
... source
address just used, and pointer is increased by four.
The recorded route address is the internet module's own internet
address ...
... being forwarded.
This procedure of replacing the source route with the recorded
route (though it is in the reverse of the order it must be in to
...
... This procedure of replacing the source route with the recorded
route (though it is in the reverse of the order it must be in to
be used as a source route) means the option (and the IP header ...
... route (though it is in the reverse of the order it must be in to
be used as a source route) means the option (and the IP header
as a whole) remains a constant length as the datagram ...
... host
IP is allowed to use any route of any number of other
intermediate gateways to reach the next address ...
... intermediate gateways to reach the next address in the route.
Must be copied on fragmentation ...
... datagram.
Strict Source and Record Route
+--------+--------+--------+---------//--------+
...
...
+--------+--------+--------+---------//--------+
|10001001| length | pointer| route data |
+--------+--------+--------+---------//--------+
Type=137
...
... Type=137
The strict source and record route (SSRR) option provides a
means for the source of an internet ...
... is the option length which includes the option type code and the
length octet, the pointer octet, and length-3 octets of route
data. The third octet is the pointer into the route data
...
... length octet, the pointer octet, and length-3 octets of route
data. The third octet is the pointer into the route data
indicating the octet which begins the next source address to be
...
... smallest legal value for the pointer is 4.
A route data is composed of a series of internet addresses.
Each internet address ...
... 32 bits or 4 octets. If the pointer is
greater than the length, the source route is empty (and the
recorded route full) and the routing ...
... greater than the length, the source route is empty (and the
recorded route full) and the routing is to be based on the
destination address field ...
... the pointer is not greater than the length, the next address in
the source route replaces the address in the destination address
field, and the recorded route ...
... source route replaces the address in the destination address
field, and the recorded route address replaces the source
address just used, and pointer is increased by four.
...
... source
address just used, and pointer is increased by four.
The recorded route address is the internet module's own internet
address ...
... being forwarded.
This procedure of replacing the source route with the recorded
route (though it is in the reverse of the order it must be in to
...
... This procedure of replacing the source route with the recorded
route (though it is in the reverse of the order it must be in to
be used as a source route) means the option (and the IP header ...
... route (though it is in the reverse of the order it must be in to
be used as a source route) means the option (and the IP header
as a whole) remains a constant length as the datagram ...
... datagram directly to the next address in the
source route through only the directly connected network
indicated in the next address ...
...
+--------+--------+--------+---------//--------+
|00000111| length | pointer| route data |
+--------+--------+--------+---------//--------+
Type=7
...
... is the option length which includes the option type code and the
length octet, the pointer octet, and length-3 octets of route
data. The third octet is the pointer into the route data
...
... length octet, the pointer octet, and length-3 octets of route
data. The third octet is the pointer into the route data
indicating the octet which begins the next area to store a route
...
... data. The third octet is the pointer into the route data
indicating the octet which begins the next area to store a route
address. The pointer is relative to this option, and the
...
... smallest legal value for the pointer is 4.
A recorded route is composed of a series of internet addresses.
Each internet address ...
... 32 bits or 4 octets. If the pointer is
greater than the length, the recorded route data area is full.
The originating host must compose this option with a large
...
... The originating host must compose this option with a large
enough route data area to hold all the address expected. The
size of the option does not change due to adding addresses ...
... size of the option does not change due to adding addresses. The
intitial contents of the route data area must be zero.
When an internet ...
... internet module routes a datagram it checks to see if
the record route option is present. If it is, it inserts its
own internet address as known in the environment into which this
...
... internet address as known in the environment into which this
datagram is being forwarded into the recorded route begining at
the octet indicated by the pointer, and increments the pointer
by four.
...
... by four.
If the route data area is already full (the pointer exceeds the
length) the datagram is forwarded without inserting the address ...
... datagram is forwarded without inserting the address
into the recorded route. If there is some room but not enough
room for a full address to be inserted, the original datagram ...