SDN and Networking Concepts Quiz

A protocol used between Autonomous Systems (ASs) to exchange routing information and find the best paths for packets traversing multiple ASs.

BGP works by advertising prefixes, which represent subnets or collections of them. Routers learn if a prefix is reachable and use this information to build forwarding tables.

A router at the edge of an AS directly connected to routers from other ASs. It's responsible for exchanging routing information between ASs.

A router that operates within an AS, connecting to other routers and hosts inside the same AS.

BGP uses this to determine the optimal route to a prefix based on policy and reachability information.

This is the process where subnets announce their presence to the rest of the Internet, informing other ASs that they're reachable.

BGP is a decentralized system, meaning each AS handles its own routing information and there is no central authority controlling the entire routing process.

BGP is asynchronous, meaning it doesn't rely on synchronized clocks or timing, adding flexibility and robustness to the routing system.

A BGP message is sent from an autonomous system (AS) to advertise the existence of a subnet with prefix 𝒙. The message indicates that 𝒙 is located in the sending AS. For example, AS3 might send a message stating "AS3 𝒙" to AS2.

When an AS receives a BGP message about a subnet 𝒙, it adds its own AS identifier to the message before passing it to its neighboring AS. This process creates a path of ASs that leads to the subnet. For example, AS2 might receive a message from AS3 saying "AS3 𝒙" and then send it to AS1 as "AS2 AS3 𝒙" indicating the route to 𝒙 goes through AS2 and then AS3.

Routers, not ASs, communicate directly with each other through semi-permanent TCP connections on port 179.

A BGP connection that connects routers in different ASs. It's the primary way for ASs to exchange routing information.

A BGP connection that connects routers within the same AS. It's used to distribute routing information within an AS.

A router in AS3 sends an eBGP message to a router in AS2 (e.g., "AS3 x"). The receiving router then sends an iBGP message to all other routers within AS2 (e.g., "AS3 x"). One of those routers then sends an eBGP message to a router in AS1 (e.g., "AS2 AS3 x"). Finally, the router in AS1 sends an iBGP message to all other routers within AS1 (e.g., "AS2 AS3 x").

BGP attributes are used to advertise routes and include information such as the AS Path and the next hop router. These attributes are crucial for routers to choose the best route for traffic.

A router chooses the best route for traffic based on multiple factors, including the BGP attributes like AS-PATH (how many ASs the path passes through) and NEXT-HOP (the next router in the path).

In BGP, when a prefix is received by an AS, it adds its own ASN to the existing AS-PATH list. This prevents routing loops by ensuring that an AS will reject an advertisement if it sees its own ASN in the path.

The IP address of a router outside the current AS that directly connects to the AS. This is used to forward traffic to the next hop towards the destination.

A router selects the route with the least cost to the NEXT-HOP router, even if this isn't the overall least-cost path to the destination. This prioritizes getting data out of the AS quickly.

This happens when a router needs to add an outside-AS prefix to its forwarding table. Both BGP (inter-AS) and an intra-AS protocol (like OSPF) are used to make this routing decision.

BGP selects the route with the least cost to the NEXT-HOP router if there is only one route. If there are multiple routes to the same prefix, further criteria are applied.

When there are multiple routes to the same prefix, BGP applies tiebreakers after considering the least cost to the NEXT-HOP router.

A policy-based value assigned to each route, with higher values indicating preference.

A metric used in BGP route selection that penalizes routes with a greater number of Autonomous System (AS) hops.

BGP's mechanism for handling tie-breakers when multiple routes remain after other selection criteria are applied.

A network architecture in which multiple servers share the same IP address, allowing clients to connect to the closest server.

Distributing content across multiple geographically dispersed servers to improve performance and availability.

A distributed database system that maps domain names to IP addresses, facilitating the resolution of hostnames.

A mechanism for selecting routes based on policy considerations and optimal paths, used in BGP to manage inter-AS routing.

Traffic entering an ISP access network must be destined for that network, and traffic leaving must originate within it.

A multi-homed ISP connected to two different backbone providers.

A policy used to prevent a multi-homed ISP from forwarding traffic between backbone providers. This strategy ensures the multi-homed ISP acts as a local access provider.

An ISP network carrying traffic with both source and destination inside its customer networks.

A rule of thumb in ISP routing where backbone networks only carry traffic with either source or destination within their customer networks, preventing free-riding.

Decisions based on routing policies take precedence in inter-autonomous system (AS) routing, while technical factors (shortest paths, bandwidth) dominate intra-AS routing.

The ability of a routing protocol to handle a large number of networks efficiently is essential for inter-AS routing, but less critical within a single AS.

OSPF allows hierarchical routing by dividing an autonomous system into areas, improving scalability and manageability within a single network.

Routing within a single Autonomous System (AS) focuses on the performance of routes, unlike inter-AS routing which emphasizes policy.

Obtaining internet connectivity involves contracting with a local ISP. The ISP provides the IP address range for your network, including addresses for servers and routers.

Your company's network prefix needs to be advertised to other ISPs for them to route traffic to your network. BGP is used by the local ISP to spread this information across the internet.

An SDN architecture separates data plane forwarding from control plane functions. Network switches handle forwarding, while the control plane manages routing, security, and other network tasks.

SDN allows for flexible network programming, enabling you to implement custom rules for traffic flow, security, or load balancing.

Flow-based forwarding, which is the foundation of SDN, directs traffic based on specific header fields. This allows for precise traffic management based on various criteria.

SDN unbundles network functionality, separating data plane switches, SDN controllers, and network control applications. This allows for greater flexibility and customization.

Applications running on the SDN controller implement network control functions like routing, firewall, and load balancing. This enables programmable control over the network behavior.