BGP and inter-domain routing in Computer Networks - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary role of BGP in inter-domain routing?

Border Gateway Protocol (BGP) is crucial for routing between different networks on the internet. What is its main function?

A To exchange routing information between different autonomous systems

B To manage routing within a single local network

C To encrypt data packets between routers

D To assign IP addresses to devices

💡 Hint

Think about how different large networks communicate routing information.

BGP is designed to exchange routing information between autonomous systems (AS), which are large networks or groups of networks under a common administration. It is not used for routing inside a local network or for encryption or IP address assignment.

📋 Factual

intermediate

Which attribute in BGP is used to select the best path when multiple routes exist?

When BGP routers receive multiple routes to the same destination, which attribute do they primarily use to decide the best path?

A MAC address

B Subnet mask

C TTL value

D AS_PATH length

💡 Hint

Consider which attribute reflects the number of networks a route passes through.

The AS_PATH attribute lists the autonomous systems a route has passed through. BGP prefers the path with the shortest AS_PATH length to avoid longer or less efficient routes.

🔍 Analysis

advanced

What happens if a BGP router receives a route with its own AS number in the AS_PATH?

Consider a BGP router that receives a route advertisement containing its own AS number in the AS_PATH attribute. What is the expected behavior?

A The router resets the BGP session with the neighbor

B The router rejects the route to prevent routing loops

C The router modifies the AS_PATH by removing its AS number

D The router accepts the route and forwards it normally

💡 Hint

Think about how BGP avoids routing loops between autonomous systems.

BGP uses the AS_PATH attribute to detect routing loops. If a router sees its own AS number in the AS_PATH, it means the route has looped back, so it rejects the route to prevent loops.

❓ Comparison

advanced

How does BGP differ from interior gateway protocols (IGPs) like OSPF in inter-domain routing?

Compare BGP with IGPs such as OSPF regarding their roles and characteristics in routing.

A BGP automatically discovers neighbors, but IGPs require manual configuration

B BGP uses link-state algorithms, whereas IGPs use path-vector algorithms

C BGP is used for routing between autonomous systems, while IGPs operate within a single autonomous system

D BGP does not support policy-based routing, unlike IGPs

💡 Hint

Think about the scope of routing each protocol handles.

BGP is designed for inter-domain routing between autonomous systems, while IGPs like OSPF handle routing inside a single autonomous system. BGP uses path-vector, and IGPs often use link-state algorithms. Neighbor discovery and policy support differ as well.

❓ Reasoning

expert

Why is BGP considered a path-vector protocol rather than a distance-vector or link-state protocol?

BGP is classified as a path-vector protocol. What reasoning best explains this classification compared to distance-vector and link-state protocols?

A Because BGP maintains the full path of autonomous systems for each route, enabling loop detection and policy enforcement

B Because BGP only shares the cost of routes without path information

C Because BGP floods link-state information to all routers in the network

D Because BGP uses shortest path first algorithm like link-state protocols

💡 Hint

Consider how BGP tracks route information differently from other protocols.

BGP keeps track of the entire path of autonomous systems a route passes through (the AS_PATH). This path information helps detect loops and apply routing policies. Distance-vector protocols share only distance metrics, and link-state protocols share topology information.