Explore fundamental concepts of Internet routing and BGP with this quiz designed to introduce key protocols, terminology, and practical routing scenarios. Assess your understanding of routing basics, BGP operation, path selection, and core networking principles.
Which type of routing protocol is Border Gateway Protocol (BGP) considered to be?
Explanation: BGP is classified as a path-vector routing protocol, which means it maintains the path information that gets updated as it passes through each router in the network. Distance-vector protocols use hop counts and do not track the full path, while link-state protocols share information about node connections. Hybrid-vector is not a standard protocol category. Only path-vector accurately describes BGP’s methodology.
On which TCP port does BGP establish its sessions between peers for exchanging routing information?
Explanation: BGP uses TCP port 179 to establish and maintain reliable connections between peers and exchange route updates. Port 25 is commonly used for email transmission, port 53 for DNS queries, and port 80 for HTTP web traffic. None of these other ports are associated with BGP operation.
What is the primary purpose of Autonomous System Numbers (ASNs) in global Internet routing?
Explanation: ASNs are used to uniquely identify networks, known as autonomous systems, which are managed under a single administrative authority and participate in BGP routing. ASNs do not label individual IP addresses or devices, nor are they used for encryption purposes. Their role is key in BGP for determining routing decisions between disparate networks.
If BGP receives multiple routes to the same destination, which path attribute does it use first to choose the best route?
Explanation: BGP checks the Local Preference attribute first when selecting the best route among multiple options for the same destination. A higher local preference is preferred. AS Path length is considered only after Local Preference if the values are equal. Next-hop IP and origin code are checked later in the selection process, not as the primary attribute.
What does a BGP router advertise to its peers when sharing routing information?
Explanation: BGP advertises IP prefixes or networks to its peers, letting them know which destinations are reachable through the advertising router. It does not advertise default gateways or MAC addresses, as those are more relevant to different layers of networking. Subnet masks are included as part of the prefix, but not shared alone.
What is the main difference between an Interior Gateway Protocol (IGP) and an Exterior Gateway Protocol (EGP) such as BGP?
Explanation: EGPs like BGP are explicitly designed for routing between separate autonomous systems, while IGPs handle routing within the boundaries of a single autonomous system. IGPs are not restricted to wireless networks, and neither protocol type is defined by their encryption capabilities. BGP specifically uses path-vector algorithms, not IGPs.
Which of the following is stored in a BGP table maintained by a router?
Explanation: A BGP table contains all the routes a router has learned via BGP, along with important attributes that help with path selection. It does not store user authentication information, active TCP connections, or DNS records. Only the routing data and route attributes related to BGP operations are kept.
How does BGP primarily prevent routing loops between autonomous systems?
Explanation: BGP uses the AS Path attribute to track which autonomous systems a route has traversed; if a router detects its own ASN in the path, it rejects the route to prevent a loop. Hop counts are used by other protocols but not by BGP for loops. Ignoring unknown routes or discarding long prefixes are not standard BGP loop prevention strategies.
What is the difference between eBGP and iBGP sessions?
Explanation: eBGP is used for routing between routers in different autonomous systems, whereas iBGP is used by routers within the same autonomous system to communicate route information. The underlying protocol, supported IP versions, and encryption requirements are not what define the difference between eBGP and iBGP.
What happens when a BGP router withdraws a previously advertised route from its peers?
Explanation: When a route is withdrawn by a BGP router, its peers will remove that route from their routing tables, ensuring traffic no longer uses that path. Ignoring the update would result in outdated routes. Increasing route priority or asking for credentials is not a behavior associated with BGP route withdrawal.