What a RIP(V1/V2) Off!

The algorithms that Routing Information Protocol is based on date back to 1957, but the protocol itself was defined in RFC 1058 in 1988, with several revisions since that time.  The first version of RIP was classful, meaning that it only recognized addressing according to the Class A, B and C groups defined for the original Internet.  Subnetting was not practical since subnet masks could not be transmitted in routing updates.  If you ever want to see what this behavior is like, issue the no ip classless command on a Cisco router and specify version 1 of RIP (which is the default unless you explicitly enable version 1).  One of the more interesting things about RIP is the maximum hop-count of 15.  When I first started in networking, that seemed silly and arbitrary, but as I gained a greater grasp of binary, it made perfect sense!  You see, RIP uses a 4-Bit metric, and in binary, that maps out as follows, using the Powers of Two we talked about earlier:
8     4     2     1                Powers of Two
1       1     1     1                Binary Digits
Binary 1111 (8+4+2+1) equals a decimal value of 15!  Simply put, RIP just can’t count any higher!  In addition, because RIP is a Distance Vector Routing Protocol, it uses the loop-prevention mechanisms we talked about previously, and sends out its entire routing table every 30 seconds.  Even the newest engineer can see the glaring limitations of RIP, and due to those shortcomings, Cisco gained huge popularity by introducing its proprietary Interior Gateway Routing Protocol (IGRP).  IGRP could measure more than just hop count and thus represented a quantum leap forward in routing technology.  Unfortunately, both these protocols still used broadcasts, and new protocols such as OSPF created far more attractive update mechanisms by utilizing multicast instead.
Classless routing changed the landscape of routing in general, and in 1993 with RFC 1388, RIP was updated to support classless routing, and with the transmission of subnet masks in routing updates, subnetting was now possible.  In addition, updates using multicast became supported, and some other improvements, although the hop-limit remained at 15.  One critical thing to keep in mind is that a feature called automatic summarization is enabled on RIPV2 by default, which summarizes networks to the nearest classful boundary—in effect, making the classless protocol act classful.  Two command to almost always use when configuring RIP are: 1. Version 2 (V1 is enabled by default) and no auto-summary (disables automatic summarization).
RIP is useful in smaller networks, but in reality is as undesirable as a cheerleader being asked to the prom by the president of the chess club (see graphic above).  As we will discuss next time, there are MUCH better choices available now.
– Joe

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