xStack
®
DGS-3400 Series Layer 2 Gigabit Ethernet Managed Sw itch
131
RIP Version 1 Message Format
There are two types of RIP messages: routing information messages and information requests. Both types use the same format.
The Command field specifies an operation according the following table:
Command
Meaning
1
Request for partial or full routing information
2
Response containing network-distance pairs from
sender’s routing table
3
Turn on trace mode (obsolete)
4
Turn off trace mode (obsolete)
5
Reserved for Sun Microsystem’s internal use
9
Update Request
10
Update Response
11
Update Acknowledgement
RIP Command Codes
The field VERSION contains the protocol version number (1 in this case), and is used by the receiver to verify which version of
RIP the packet was sent.
RIP 1 Message
RIP is not limited to TCP/IP. Its address format can support up to 14 octets (when using IP, the remaining 10 octets must be
zeros). Other network protocol suites can be specified in the Family of Source Network field (IP has a value of 2). This will
determine how the address field is interpreted.
RIP specifies that the IP address, 0.0.0.0, denotes a default route.
The distances, measured in router hops are entered in the Distance to Source Network, and Distance to Destination Network
fields.
RIP 1 Route Interpretation
RIP was designed to be used with classed address schemes, and does not include an explicit subnet mask. An extension to version
1 does allow routers to exchange subnetted addresses, but only if the subnet mask used by the network is the same as the subnet
mask used by the address. This means the RIP version 1 cannot be used to propagate classless addresses.
Routers running RIP version 1 must send different update messages for each IP interface to which it is connected. Interfaces that
use the same subnet mask as the router’s network can contain subnetted routes, other interfaces cannot. The router will then
advertise only a single route to the network.
RIP Version 2 Extensions
RIP version 2 includes an explicit subnet mask entry, so RIP version 2 can be used to propagate variable length subnet addresses
or CIDR classless addresses. RIP version 2 also adds an explicit next hop entry, which speeds convergence and helps prevent the
formation of routing loops.
RIP2 Message Format
The message format used with RIP2 is an extension of the RIP1 format:
RIP version 2 also adds a 16-bit route tag that is retained and sent with router updates. It can be used to identify the origin of the
route.
Because the version number in RIP2 occupies the same octet as in RIP1, both versions of the protocols can be used on a given
router simultaneously without interference.
RIP