Information Technology Reference
In-Depth Information
Figure 5-1
Encapsulated RIPv1 Message (Answer)
Data Link Frame
Header
IP Packet
Header
UDP Segment
Header
RIP Message
(512 Bytes; Up to 25 Routes)
Data Link Frame:
MAC Source Address = Address of Sending Interface
MAC Destination Address =
Broadcast: FF-FF-FF-FF-FF-FF
IP Packet:
IP Source Address = Address of Sending Interface
IP Destination Address =
Protocol Field =
17 for UDP
Broadcast: 255.255.255.255
UDP Segment:
Source Port =
Destination Port =
520
520
RIP Message:
Command:
(1);
(2)
Version = 1
Address Family ID = 2 for IP
Routes: Network IP Address
Metric:
Request
Response
Hop Count
RIP Message Format: RIP Header
Figure 5-2 shows the detail of a RIPv1 message. Fill in the missing field content.
Figure 5-2
RIPv1 Message Format (Answer)
0
7
8
15
16
23
24
31
Command = 1 or 2
Address Family Identifier (2 = IP)
IP Address (Network Address)
Version = 1
Must be Zero
Must be Zero
Route
Entry
Must be Zero
Must be Zero
Metric (Hops)
Multiple Route Entries, upto a maximum of 25.
RIP Message Format: Route Entry
The route entry portion of the message includes three fields with content:
Address family identifier
,
IP address
, and
Metric
. This route entry portion represents one destination route with its associated
metric. One RIP update can contain up to
25
route entries. The maximum datagram size is
512
bytes,
not including the IP or UDP headers.
RIP Operation
RIP uses two message types specified in the Command field:
Request
message and
Response
mes-
sage. Each RIP-configured interface sends out a
Request
message on startup, requesting that all RIP
neighbors send their complete routing tables. A
Response
message is sent back by RIP-enabled neigh-
bors. When the requesting router receives the responses, it evaluates each route entry. If a route entry
is new, the receiving router installs the route in the routing table. If the route is already in the table,
