5: Routing Flashcards
What is policy-based routing?
Routing as per specifications of policy by an AS network admin, e.g. don’t route through another AS and if/when to advertise paths to neighboring ASes.
What is forwarding?
The process by which a datagram is moved from a source device to an output device: 1 hop along a path.
What are the types of BGP message?
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What is a routing protocol?
A protocol specifying how routers in a network communicate, forwarding tables in routers are built, and paths of data between two endpoint nodes are chosen.
What plane does routing happen on?
The control plane
What is the network control plane?
The part of the router architecture that is concerned with drawing the network topology, or the information in a (possibly augmented) routing table that defines what to do with incoming packets.
How may the network control plane be structured?
With per-router control (traditional) or logically centralised control (software-defined networking).
How does the Distance vector algorithm work?
Each node stores its distance estimates to other nodes, and other nodes use its distance estimates to other nodes to estimate their distances to their nodes; for instance, the distance of a node x to get to node z via node y = the distance of x to y the estimated distance of y to z that y informs x of.
In this manner, it is a recursive algorithm. Estimated costs only update when their neighbours do, and starter changes only change due to changes in a local link. It is distributed that changes only occur when neighbours do, so they propagate.
What are eBGP and iBGP connections?
Connections external and internal to an AS that advertise the availability of the nodes in a subnet to the rest of the network and vice versa.
Why are there different protocols for inter and intra AS routing?
different weights on policy and performance in the two
What is global and decentralised information?
In networks with global information, all routers know the complete topology and the link cost information. In networks with decentralised information, a router only knows the link costs to its neighbours.
What are static and dynamic routing algorithms?
Static routes change more slowly over time, whereas dynamic routes change more rapidly, often periodically updating in response to link cost changes.
What is Dijkstra’s algorithm?
An algorithm to find the shortest paths between nodes in a graph.
How do link state and distance vector algorithms compare?
In link-state algorithms, all routers independently calculate the best path for data, being aware of all router links and having the entire routing algorithm logic. This contrasts with distance-vector protocols, in which each router’s routing table is recursively dependent on all others.
Link-state algorithms more resistant against router malfunction: nodes only compute its own table rather than tables using each other in DV, where errors propagate.
n ^ 2 complexity LS algorithms converge in O(n * E) messages, where n = no nodes, E = no links, and DV convergence time varies
How does Dijkstra’s algorithm work?
It finds the costs of going between all adjacent nodes, then the minimum cost of going between all nodes 2 hops apart, then 3, then 4, etc, to build a forwarding table of the minimum cost path between any 2 nodes on the graph.
What is a distance vector?
An array (vector) of diatances to other ndoes in the network from a given node.
