Test 2

Network Layer

transport segment from sending to receiving host

sender

encapsulates segments into datagrams, passes to link layer

receiver

delivers segments to transport layer protocol

hosts routers

devices that have network layer protocols:

routers

1. examines header fields in all IP datagrams passing through it.
2.moves datagrams from input ports to output ports to transfer datagrams along end-end path.

forwarding

move packets from a router's inout link to appropriate router output link
- Getting through single interchange

routing

determine route taken by packets from source to destination (routing algorithms)
- process of planning trip from source to destination

transport

layer is only needed at beginning and end

Ethernet

what switch has no network layer because it has no router?

data control

What are the planes of a network layer?

data plane

- local per-router function
- determines how the arriving datagram will be forwarded to output
-touches user data

control plane

- network wide logic
- determines how datagram is routed among routers along end-end path from source host to destination host.
- example : traditional routing algorithms

routing algorithm

each router that interact in the control plane has an individual

successful datagram delivery to destination , timing or oder of delivery , bandwidth available to end-end flow

Internet "best effort" service model has no guarantees on :

simplicity of mechanism

has allowed internet to be widely deployed adopted

provisioning of bandwidth

sufficient __________________ allows of performance of real time apps (video) to be "good enough" for "most of the time"

replicated application layer distributed services

(data centers, content distribution networks) connecting close clients networks, allow services to be provided from multiple locations

control plane

which plane operates in millisecond scale and is software

data plane

which plane operates in nanosecond time scale and is hardware

line termination , link layer protocol , lookup forwarding queuing

router input functions are:

physical

line termination is a __________ layer and has bit-level reception

input port queuing

if datagram arrive faster than forwarding rate into switch fabric

lookup

using header field values to ________ output port using forwarding table in input port memory

line speed

goal of decentralized switching is to complete input port processing at

destination based forwarding

forward based only on destination IP address (traditional)

longest prefix match

use longest address that matches destination address

switching fabric

transfer packet from input link to appropriate output link

switching rate

- rate at which packet can be transferred from input to output
- measured as multiple of input/output line rate.
- N inputs: switching rate N times line rate desirable

rate : N ( input ports) x R (routing)

shared memory, shared bus and interconnection network

types of switching fabrics:

shared memory

- used in first generation routers with switching under CPU
- packet is copied to memory
- speed limited by memory bandwidth (2 bus crossing per datagram)

shared bus

- datagram from input port memory to output port memory via shared bus
- has bus contention (1 thing at a time)
- 32 Gbps bus, Cisco 5600: access routers

bus contention

switching speed limited by bus bandwidth

interconnection network

- change packets with constant time rate
- break up to fragments and reassemble datagram at exit
- has multistage switch NxN
- exploiting parallelism

multistage switch

nxn switch from multiple stages of smaller switches

crossbar , clos networks

examples of interconnection nets initially developed to connect processors in multiprocessor.

scaling

using multiple switching planes in parallel

cisco crs router

- basic unit has 8 switching planes
- each plane has 3 stage interconnection network
- up to 100s Tbps switching capacity

head of line queuing

queued datagram at front of queue prevents others in queue from moving forward

buffering

required when datagrams arrive from fabric faster than link transmission , datagrams can be lost due congestion and lack of buffers

scheduling discipline

chooses among queued datagrams from transmission, priority scheduling

output port buffer overflow

queuing and loss due to ____________

tail drop and priority

types of dropping

marking

which packets to mark signal congestion

front

if we have a TCP , we drop the _____ because the destination will have early acknowledgment (duplicate ack)

FCFS

FIRST COME FIRST SERVE packets transmitted in order of arrival to output port (FIFO : first in firs out)

priority scheduling

- classified as classes ( think airport example) any header fields can be used to classify

Round robin

cued by class and go around and take one from each class.

weighted far queuing

generalized round robin , weighted amounts wi / sum of wj

path selection algorithms , IP protocol , ICMP protocol

network layer functions:

path selection algorithm

implemented in routing protocols OSPF, BGP

IP protocol

- datagram format
- addressing
- packet handling conventions

ICMP protocol

- error reporting
- router signalling

IP address

32-bit identifier associated with each host or router interface

32

IP address __ bit identifier associated with each host or router interface

interface

connection between host/router and physical link
- routers have multiple ________
- host has one or two ____________

subnet

device interfaces that can physically reach each other without passing through an intervening router (bubble)

subnet part

devices in the same subnet have common high order bits of IP address structure

host part

low order bits of IP address structure

subnet

each isolated network is called a

host router

to define subnet we detach each interface from its ______ or __________

Classless Interdomain routing

CIDR : a.b.c.d/x

bits

a.b.c.d/x : the x is the number of _________

hardcoded by sysadmin and DHCP

how does host get IP address?

dynamic host configuration protocol

DHCP : dynamically gets address from as server

DHCP

host dynamically obtain IP address from network server when it joins the network
- can renew its lease on address in use
- allows reuse of addresses
- support for mobile user to join/leave network

discover offer request ack

Set of steps for DHCP: DHCP ____

router

DHCP server is located in _____________

hierarchical addressing

allows efficient advertisement of routing information

NAT

network adress transfer

ope IPv4

all devices in local network share just _____ ________ address as far as outside world is concerned

32 bit

How big is the address of the IP address that can be only be used in local network?

one external IP address for depletion, security (outside not accessible)

What are the advantages of NAT?

depletion from 32 to 128

main goals of address ipv4 address

speed processing/forwarding (40 byte header) , enable different network layer treatment of flows

secondary goals to fix IPv4

priority

identify priority among datagrams in flow in IPv6

flow label

identify datagrams in same "flow"

128 bits

size of source address and destination address ?

checksum, fragmentation , options

what is missing in IPv6 instead of IPv4

tunneling

IPv6 datagram carried as payload in IPv4 datagram among IPv6 routers "packets in packets"

IP

in the protocol hourglass, what is the middle network layer?

connectivity , IP Protocol , Intelligence complexity at edge

Three cornerstone beliefs of the internet

per-router control and logically centralized control

two approaches to structuring network control plane:

control plane

individual routing algorithm components in each and every router interact in the ____________ _________

routing protocol

The goal of __________ __________ : determine good paths from sending host to receiving host through network of routers

path

sequence of routers packets traverse from given initial source host to final destination host

cost, fast, congestion

What makes a "good" path?

routers , links

graph G = ( N is set of _______ , E is a set of ________)

link state broadcast

how to get link costs to all nodes?

node

Each ______ computes least cost paths from itself to all other noes and produces a forwarding table

iterative

Dijkstra's link-state routing algorithm is _____________ : after k iterations, know least cost path from itself to k

Cxy

direct link cost from node x to y , infinity if not direct neighbors

D(v)

current estimate of cost of least-cost-path from source to destination v

p(v)

predecessor node (before v) along path from source to v

N'

set of nodes whose least-cost-path already found

least cost path tree

when finding shortest path to all nodes from source we call the final result a ________ ________ _________ __________

distance vector

each node send sits own _______ _______ estimate to neighbors

distance vector

Dx(y) = minv { cx,y + Dv(y) } is the equation of ___________ ____________

wait for change , recompute DV , notify if changes happen

distance vector algorithm has these three steps:

link cost changes , DV update

when does an iteration happen for the distance vector ?

asynchronous

Distance algorithm is __________ since there is no lock in step among the nodes for each iteration