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91 lines
2.2 KiB
Markdown
91 lines
2.2 KiB
Markdown
---
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title: "20-network-layer-control-plane"
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aliases:
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tags:
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- cosc203
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- lecture
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---
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# per-router control vs SDN
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## per router
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- each router runs a routing algorithm
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- router communicate with each other
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- and creates a forwarding table
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## SDN software defined networking
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a remote controller computes, and install fowarding tables in routers
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- much faster: less work for each router
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- separate control and data plane
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# routing algorithms
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- goal is to determine "good" paths from sending to recieving host through network of routers
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- path: sequence of routers
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- "good": least "cost", "fastest", "least congested"
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## graph abstraction
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- nodes: set of routers
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- edges: set of links
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$c_{a,b}$ cost the link directly connecting a and b. if there is no link the cost is ♾
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## algorithm classification
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global: all routers have complete toplogy, link cost into
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- link state algotihms
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decentralized: interative process of computation, exchange of into with neighbors
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- routers only know link costs to attacked neighbors
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- "distance vecotr algorithms
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static: routes change very slowly over time
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dynamic: routes change more quickly
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- periodic updates or in response to link cost changes
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## link state routing
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centralized: network topology, link costs are known to all nodes
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- each node gathers informatin on each link to its neighbors
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- build link state packets and flood to all other nodes
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computes least costs paths from one node to all other nodes
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- gives a fowarding table for that node
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iterative: after k interations, know least cost path to k destinations
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## notations
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## Dijkstra's algorithm
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foward search algorithm
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```
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///initialization
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N` = {u}
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for all nodes v
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if v adjacent to u
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then D(v) = Cuv
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else D(v) = infinity
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//loop
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loop until all nodes in N`
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find W not in N` such that D(w) is a min
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add w to N`
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update D(v) for all v adjacent to w and not in N`:
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D(v) = min(D(v), D(w)+Cwv)
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//new least-path-cost to v is either old least-cost-path to v or known least-path-cost to w plus direct-cost from w to v
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```
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complexity:
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- n nodes
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- O(n)
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# routing in the internet
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# ICMP |