RFC1582 - Extensions to RIP to Support Demand Circuits( 八 )

routing database.
Only the first 4 octets of the packet format shown in
figure 2 are sent, since all routing information is
implied by this request type.
TRIGGERED RESPONSE (7)
A message containing all of the sender"s routing
database, excluding those entries learned from the
interface to which the routing information is being
sent.
This message may be sent in response to a triggered
request, or it may be an update message resulting
from a change in the routing database.
A triggered response message MUST be sent in response
to a triggered request message even if there are no
routes to propagate. This would be the case for a
host which had a WAN interface only, but which wished
to run the triggered update protocol.
0 1 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
command (1)version (1)must be zero (2)
--------------- --------------- -------------------------------
The following new fields are inserted for some commands
0 1 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
sequence number (2)fragment (1) no of frags (1)
------------------------------- -------------------------------
Followed by up to 25 routing entries (each 20 octets)
0 1 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
address family identifier (2)must be zero (2)
------------------------------- -------------------------------
IP address (4)
---------------------------------------------------------------
must be zero (4)
---------------------------------------------------------------
must be zero (4)
---------------------------------------------------------------
metric (4)
---------------------------------------------------------------
.
.
The format of an IP RIP datagram in octets, with each tick mark
representing one bit. All fields are in network order.
The four octets: sequence number (2), fragment number (1) and
number of fragments (1) are not present in the original RIP
specification. They are only present if command takes the
values 7 or 8.
Figure 2. IP Routing Information Protocol packet format
TRIGGERED ACKNOWLEDGEMENT (8)
A message sent in response to every triggered response
packet received.
Only the first 8 octets of the packet format shown in
figure 2 are sent.
VERSION In this instance Version 1.
SEQUENCE NUMBER
This is a new field inserted if command takes the values 7
or 8.
The sequence number MUST be incremented every time updated
information is sent out on a WAN. The sequence number
wraps round at 65535.
When a triggered acknowledgement is sent the sequence
number is set to the same value as the triggered response
packet being acknowledged.
The sequence number MUST be identical over fragments. If a
fragment is retransmitted the sequence number MUST not
change.
FRAGMENT NUMBER
The fragment number is one for the first fragment of a
routing update, and is incremented for each subsequent
fragment. A fragment can contain up to 25 routing entries.
When a triggered acknowledgement is sent the fragment
number is set to the same value as the triggered response
packet being acknowledged.
NUMBER OF FRAGMENTS
In a triggered response packet this indicates the number of
packets required to complete the routing update.
This field has no relevance for triggered acknowledgement