Cracking the Coding Interview, 4 Edition - 150 Programming Interview Questions and Solutions

Solutions to Chapter 17 | Networking
17.2 Explain any common routing protocol in detail. For example: BGP, OSPF, RIP.
SOLUTION
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Depending on the reader’s level of understanding, knowledge, interest or career aspirations,
he or she may wish to explore beyond what is included here. Wikipedia and other websites
are great places to look for a deeper understanding. We will provide only a short summary.
BGP: Border Gateway Protocol
BGP is the core routing protocol of the Internet. “When a BGP router first comes up on the
Internet, either for the first time or after being turned off, it establishes connections with
the other BGP routers with which it directly communicates. The first thing it does is download
the entire routing table of each neighboring router. After that it only exchanges much
shorter update messages with other routers.
BGP routers send and receive update messages to indicate a change in the preferred path
to reach a computer with a given IP address. If the router decides to update its own routing
tables because this new path is better, then it will subsequently propagate this information
to all of the other neighboring BGP routers to which it is connected, and they will in turn
decide whether to update their own tables and propagate the information further.”
Borrowed from http://www.livinginternet.com/i/iw_route_egp_bgp.htm.
RIP: Routing Information Protocol
“RIP provides the standard IGP protocol for local area networks, and provides great network
stability, guaranteeing that if one network connection goes down the network can quickly
adapt to send packets through another connection. “
“What makes RIP work is a routing database that stores information on the fastest route
from computer to computer, an update process that enables each router to tell other routers
which route is the fastest from its point of view, and an update algorithm that enables
each router to update its database with the fastest route communicated from neighboring
routers.”
Borrowing from http://www.livinginternet.com/i/iw_route_igp_rip.htm.
OSPF: Open Shortest Path First
“Open Shortest Path First (OSPF) is a particularly efficient IGP routing protocol that is faster
than RIP, but also more complex.”
The main difference between OSPF and RIP is that RIP only keeps track of the closest router
for each destination address, while OSPF keeps track of a complete topological database of
all connections in the local network. The OSPF algorithm works as described below.
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