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Assignment on routing protocols

Daniel Hansen
CIE 333
Question 1
Distance vector Routing
Routers running distance vector algorithms advertise the vector (path) and distance (metric) for
each destination reachable within the network to adjacent (directly connected) peers. This
information is placed in a local database as it is received, and some algorithm is used to determine
which path is the best path to each reachable destination. Once the best path is determined, these
best paths are advertised to each directly connected adjacent router.
Two common algorithms used for determining the best path are Bellman-Ford, which is used by
the Routing Information Protocol (RIP and RIPv2), and the Diffusing Update Algorithm (DUAL),
used by the Enhanced Interior Gateway Protocol (EIGRP).
It is a dynamic routing algorithm in which each router computes distance between itself and
each possible destination i.e. its immediate neighbors.
The router share its knowledge about the whole network to its neighbors and accordingly
updates table based on its neighbors.
The sharing of information with the neighbors takes place at regular intervals.
It makes use of Bellman Ford Algorithm for making routing tables.
Problems – Count to infinity problem which can be solved by splitting horizon.
– Good
– Persistent looping problem i.e. loop will be there forever.
Bandwidth required is less due to local sharing, small packets and no flooding.
Makes use of Bellman Ford algorithm.
Traffic is less
Link State Routing
Link state protocols, such as IS-IS and OSPF, rely on each router in the network to advertise the
state of each of their links to every other router within the local routing domain. The result is a
complete network topology map, called a shortest path tree, compiled by each router in the
network. As a router receives an advertisement, it will store this information in a local database,
typically referred to as the link state database, and pass the information on to each of its adjacent
peers. This information is not processed or manipulated in any way before it is passed on to the
router's adjacent peers. The link state information is flooded through the routing domain
unchanged, just as the originating router advertises it.
As each router builds a complete database of the link state information as advertised by every other
router within the network, it uses an algorithm, called the shortest path first algorithm, to build a
tree with itself as the center of that tree. The shortest path to each reachable destination within the
network is found by traversing the tree.
It is a dynamic routing algorithm in which each router shares knowledge of its neighbors
with every other router in the network.
A router sends its information about its neighbors only to all the routers through flooding.
Information sharing takes place only whenever there is a change.
It makes use of Dijkastra’s Algorithm for making routing tables.
– Heavy
– Flooding can result in infinite looping which can be solved by using Time to leave
(TTL) field.
Bandwidth required is more due to flooding and sending of large link state packets
It is based on global knowledge (about the entire network).
Makes use of Dijkastra’s algorithm
Traffic is more
Converges faster
Path Vector Routing protocol
A path vector protocol does not rely on the cost of reaching a given destination to determine
whether each path available is loop free or not. Instead, path vector protocols rely on analysis of
the path to reach the destination to learn if it is loop free or not. Path vector (PV) protocols, such
as BGP, are used across domains aka autonomous systems. In a path vector protocol, a router
does not just receive the distance vector for a particular destination from its neighbor; instead, a
node receives the distance as well as path information (aka BGP path attributes), that the node
can use to calculate (via the BGP path selection process) how traffic is routed to the destination
Question 2
The Metric used in RIP is hop counts
The Metric used in OSPF is cost. Its formula is Reference bandwidth divided by interface
The Metrics used in EIGRP is Bandwidth, Load, Delay, Reliability and MTU. Its formula is
256 * { K1*BW + [(K2*BW)/(256-load)] + (K3*delay) } * {
K5/(reliability+K4) }