Internetworking: Revision Questions Answers

Internetworking: Revision Questions
What are the key characteristics of:
Distance Vector
- Has periodic updates, at the end of a given period of time, updates will be
sent to any router taking part in distance vector protocol.
- Has neighbours whom with which they routing information
- Broadcasts to find the available neighbours
Link – State
- Uses Dijkstra algorithm
- Use cost as the parameter for best path calculation
- Link state updates part the network
- Updates are triggered by changes in network topology
- Has fast time convergence
- Uses hierarchical structure
Path Vector
- Uses path to reach the destination
- Is a loop free protocol
What are the characteristics of:
- Internal routing protocols IGP is a Routing Protocol which is deployed to look
for a network path information within an internal network routing.
external routing protocols
- Exterior Gateway Protocol (EGP) is a Routing Protocol which is deployed to
find network route information between different ASs.
Explain the main functions of RIP
- Is a distance routing protocol which uses hop count as the main metric. This
protocol defines how the routers are supposed to share information during
the moving of the traffic among the interconnected group of LANs.
What are the main limitations of the routing protocol?
- RIP cannot support a network which has more than fifteen hops within the
same network
- Does not support the variable-length subnet mask.
- Has limited security
- Has slower convergency time.
What timers can be found in RIP?
- Invalid timer – a route is declared invalid after 180 sec
- Update – takes place 30 sec
- Hold down – timer which happens after hold down timer after 180 sec
- Flush time – timer which expire after route entry has been removed from
routing table 240 sec.
How does each work?
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- See explanation after each above.
How do they relate to each other?
- The update timer updates after every 30 sec, invalid timer is triggered when
there has been no update after 180 sec, the hold-down timer is activated as
soon as the route has been declared invalid and the flush which is set to
240 resets the route once it has stayed in for 240 sec
How does RIP manage to maintain its routing table up-to-date?
- RIP maintains its routing table up-to-date by broadcasting its entire routing
table to its closest neighbours.
Explain the main functions of OSPF
- OSPF is a routing protocol which is used to find the best path during their
passing through a number of linked networks.
Explain the key advantages of OSPF over RIP
- Supports VLSM: the OSPF supports the classless routing
- Network reachability: OSPF is able to support networks which have more
than 15 hops.
- Fast convergence: the OSPF converges fast as compared to RIP
- Metric: OSPF uses costs as its metric as compared to hop count for RIP
which is very slow.
- Efficiency: RIP’s 30 seconds frequent updates makes it inefficient.
What is an Autonomous System?
- This is a globally assigned unique number. The autonomous system share
information with autonomous system by use of BGP.
What is an OSPF area?
- An OSPF network can be divided into sub-domains called areas. An area is a
logical collection of OSPF networks, routers, and links that have the same
area identification.
What is a Link State Database? How is it used?
- This is a tree image of the of the OSPF topology holding all the OSPF routing
information. The Link state Database is used to sore the routing information
of the OSPF routing.
What is Link State Advertising (LSA)? How is it used?
- This is an OSPF data packet which contains link-state advertisement
together with the information which is share between OSPF routers.
What are the five steps to initiate routing in an OSPF area?
i. Establishment of the neighbour adjacencies.
ii. Exchange of the link-state advertisements
iii. Topology table building
iv. SPF algorithm execution
v. Routing table building
How does OSPF manage to maintain its routing table up-to-date?
- Hello protocol is used to maintain the routing-table by providing dynamic
discovery of neighbour relationships
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