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CS 6250 Test 3/92 Questions and Answers/100% Graded
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CS 6250 Test 3/92 Questions andAnswers/100% Graded
Network Management - -configuring network to achieve variety of tasks,
including load balance, security, business relationships.
-What happens when a network is not configured correctly? - -this can lead
to persistent oscillation, loops, partitions, "black holes"
-why is configuration hard? - -1.Defining correctness is hard
2.Interactions between protocols can lead to unpredictability
3.Each as is independently configured, which can lead to issues between
AS's
4.Operators make mistakes.
-Software defined networking - -network wide views of topology and traffic,
ability to satisfy network level objectives, direct control. SDN allows an
operator to write a control program that directly affects the data plane.
remove routing at routers, perform routing computation at logically
centralized controller
-routers should - -Forward packets
Collect measurements (traffic stats and topology info)
-routers should not - -compute routes. these should be logically centralized
-data plane - -forward traffic according to control plane logic
Forwarding (at ip layer), switching (at layer 2)
-control plane - -logic that controls forwarding behavior
Routing protocols, configuration for network middleboxes
-effect of separating data and control plane - -Separation of data and
control allows network operator to build network with devices where the
control resides in a separate control program. This allows us to move from a
vertically integrated network to a network with open interfaces that can be
controlled by software and allow much more rapid innovation.
-SDN advantages - -coordination, evolution, reasoning
-SDN applications - -Data center
Backbone networks
Enterprise networks
Internet exchange points
, Home networks
-why is separating data and control plane a good idea? - -Independent
evolution of the network. Software and hardware can evolve independently
Control from a high level program. debug/check behavior more easily
-construct a firewall - -build hash table with key value pairs where table
maps a switch and source mac address to a true or false value depending on
whether traffic should be forwarded or dropped.
Controller may only forward packet if firewall entry maps to true.
-Problems with updates in SDNs - -Problems: updates may disrupt packets
along an end to end path. This is a packet level consistency problem.
Updates to multiple switches may result in problems
Packets from the same flow may be subject to two different network states.
This is a flow level consistency problem.
-solution to switches having a limited number of rules - -Solution:
dynamically unfold rules as traffic arrives. Programmer specifies
"GroupBy(srcip)"
Runtime dynamically adds rules as traffic arrives. Guaranteeing there are
only rules in the switch that correspond to active traffic
-consistency arises in two steps - -1. Controller may read state from
network switches at different times, resulting in inconsistent view.
2. Controller may write policy as traffic actively flows through network, which
could disrupt packets on an end to end path or packets that should be
treated consistently because they are part of the same flow
-What if more packets arrive at switch before controller can install rule for
that flow? - -Solution: programmer specifies a limit of 1 so application only
sees first packet in the flow and subsequent packets are suppressed.
Runtime system then hides the extra events
-solutions to reading state problems - -predicates, unfolding, suppression
-Network Virtualization - -Abstraction of physical network where multiple
logical networks can be run on the same shared physical substrate
-network hypervisor - -arbitrates access to underlying physical network to
multiple physical networks, providing illusion that each virtual network has
its own physical network.
-why use virtual networking? - --ossification of internet architecture
-Network virtualization enables evolution by letting multiple architectures
exist in parallel.
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