The justifications of maintaining old RIP in a world of newer and stronger routing protocols are mainly its vast distribution and its small overhead requirements both in bandwidth and in configuration and management time. In addition, RIP is very easy to implement, especially in relation to the newer IGPs. Under the assumption that RIP will remain in service for some more years, there were people who thought it was reasonable to increase RIP's usefulness, especially since the gain looked far greater than the expense of the change.
Recently, RIP version 2 became the standard version of RIP, and the original RIP is now historic.
The main disadvantages of RIP version 1 are the minimal amount of information included in every packet, the large amount of unused space in the header of each packet and the ignorance from implementations and topics which postdated RIP 1. Namely, autonomous systems and basically EGP interactions, sub-netting, and authentication.
The RIP 2 datagram format is:
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Command (1) | Version (1) | Routing domain |
+---------------+---------------+-------------------------------+
| Address Family Identifier (2) | Route Tag (2) |
+-------------------------------+-------------------------------+
| IP Address (4) |
+---------------------------------------------------------------+
| Subnet Mask (4) |
+---------------------------------------------------------------+
| Next Hop (4) |
+---------------------------------------------------------------+
| Metric (4) |
+---------------------------------------------------------------+
The Command, Address Family Identifier (AFI), IP Address, and Metric all have the same meanings as in RIP 1. The Version field specifies version number 2 for RIP datagrams which use authentication or carry information in any of the newly defined fields.
In RIP 2 there is an optional authentication mechanism. When in use, this option abuses an entire RIP entry, and leaves space to at most 24 RIP entries in the remainder of the packet. The most widespread authentication Type is simple password and it is type 2.
The Routing domain field enables some routing domains inter-work upon the same physical infrastructure, while logically ignoring each other. This gives the ability to simply implement various kinds of policies. There is a default routing domain which is assigned the value '0'.
The Route Tag (RT) field exists as a support for EGP's. This field is expected to carry Autonomous System numbers for EGP and BGP. RIP systems which receive RIP entry which contains a non-zero RT value must re-advertise that value.
The Subnet Mask field contains the subnet mask which is applied to the IP address to yield the non-host portion of the address. If this field is zero, then no subnet mask is included for this entry.
Next Hop is the immediate next hop IP address to which packets to the destination specified by this route entry should be forwarded. The purpose of the Next Hop field is to eliminate packets being routed through extra hops in the system. It is particularly useful when RIP is not being run on all of the routers on a network.
Multi-casting is an optional feature in RIP 2 using IP address 224.0.0.9. This feature reduces unnecessary load on those hosts which are not listening to RIP 2. The IP multi-cast address is used for periodic broadcasts. In order to maintain backwards compatibility, the use of the multi-cast address is configurable.
RIP 2 is totally backwards compatible with RIP 1. Its applications support fine tuning to be RIP 1 emulation, RIP 1 compatible, or fully RIP 2.
