8. Routing Flashcards
(16 cards)
Multiple Choice
Which of the following tasks is NOT performed by a router?
Clarifier: Choose the task that routers do not do among forwarding, routing table updates, packet encapsulation, and path selection.
Routing and Forwarding
C) Packet encapsulation
Clarifier: Routers forward packets, update routing tables, and select paths, but packet encapsulation is done at the Data Link or Physical layer, not the router.
Packet encapsulation is typically done at lower layers (Data Link/Physical). Routers operate mainly at the Network layer, forwarding packets and updating routing tables.
True/False
The optimality principle states that if router J lies on the optimal path from router I to router K, then the optimal path from J to K also lies along the same route.
Optimality Principle
True
This principle ensures that subpaths of an optimal path are themselves optimal, forming a sink tree rooted at the destination.
Open-Ended
Explain the main difference between distance vector routing and link state routing.
Comparison between the two primary routing algorithm categories.
Distance vector routing relies on routers exchanging distance vectors with neighbors to update routes, while link state routing requires routers to flood link state packets to all routers to build a complete network map.
Distance vector uses neighbor info only; link state routers have full network topology, enabling them to compute shortest paths individually.
Multiple Choice
What problem does the ‘count to infinity’ issue primarily affect?
Clarifier: Select the routing algorithm most impacted by this problem.
Count to Infinity Problem
B) Distance Vector Routing
Clarifier: This problem arises when distance vector protocols slowly converge on route failures.
Distance vector algorithms can suffer slow convergence and loops causing the ‘count to infinity’ problem; link state protocols do not have this issue.
True/False
Flooding is a practical routing method used commonly in large-scale networks.
Usefulness and practicality of flooding routing.
False
Flooding sends packets out all outgoing lines, causing excessive overhead; it’s mainly used for special cases like testing or emergency networks.
Open-Ended
Describe one method to reduce duplicate packets during flooding.
Techniques to control flooding overhead.
Using a hop counter that decrements at each hop, or keeping track of flooded packets to avoid resending duplicates.
Hop count limits packet lifetime; tracking prevents multiple transmissions of the same packet.
Multiple Choice
In the Distance Vector Routing algorithm, what does a router do when it receives routing information from a neighbor?
Clarifier: Select the correct update action the router takes.
Distance Vector table update mechanism.
C) Adds one hop to the cost received and updates its table if the new cost is lower or the route is new.
Clarifier: Routers update their routing tables based on neighbors’ info, incrementing the cost metric.
Routing info received includes neighbor’s cost to destinations; router adds its cost to neighbor and updates its own table accordingly.
True/False
Split horizon with poison reverse is a technique to prevent routing loops in distance vector protocols.
Loop prevention techniques in routing.
True
Split horizon prevents advertising a route back on the interface it was learned from; poison reverse advertises it with an infinite metric to break loops.
Open-Ended
What is the main purpose of hierarchical routing?
Hierarchical routing benefits and motivation.
To reduce routing table size and routing overhead in large networks by dividing the network into regions or areas.
Hierarchical routing limits routing information scope, improving scalability and efficiency in large-scale networks.
Multiple Choice
Which of the following routing protocols is an example of an exterior gateway protocol (EGP)?
Clarifier: Choose the protocol that routes between autonomous systems.
Distinguishing interior vs exterior routing protocols.
D) Border Gateway Protocol (BGP)
Clarifier: BGP handles routing between autonomous systems on the Internet.
RIP and OSPF are interior protocols used inside ASes; BGP is the standard inter-AS protocol.
True/False
OSPF uses a link state routing algorithm and can assign different weights to links based on service types.
OSPF characteristics.
True
OSPF is a link state protocol that supports cost metrics including hop count and differentiated service weights.
Open-Ended
Briefly describe the purpose of a HELLO packet in link state routing.
Neighbor discovery and link cost measurement.
HELLO packets are used to discover neighbors, confirm connectivity, and measure link delay by exchanging time stamps.
HELLO exchanges allow routers to learn neighbor IDs and link metrics needed to build link state packets.
Multiple Choice
What is the maximum hop count allowed in RIP before a route is considered unreachable?
Clarifier: RIP’s limit for path cost to prevent loops.
RIP hop count limits.
C) 15
Clarifier: A hop count of 16 is considered infinite, meaning unreachable.
RIP uses a maximum cost of 15 hops to limit network size and prevent routing loops.
True/False
In the Border Gateway Protocol (BGP), the path vector algorithm stores the full path of autonomous systems a route traverses.
BGP routing table contents.
True
BGP includes the full AS path in its routing information to enforce policies and prevent loops.
Open-Ended
What role does an Autonomous System (AS) play in Internet routing?
AS definition and significance.
An AS is a collection of IP networks under a common administrative domain that runs its own routing policies and protocols.
ASes are the building blocks of Internet routing; each AS uses interior protocols internally and BGP externally.
