CS 91: Cloud Systems & Datacenter Networks Networks Background

(1)

CS 91: Cloud Systems &

Datacenter Networks

(2)

(3)

Agenda

• _{Overview
of
tradiBonal
network
topologies}

• _{IntroducBon
to
soEware-‐deﬁned
networks}

(4)

Topology

• _{Shape
and
structure
of
the
network}

“Star” or

“Hub and spoke” “Bus”

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Topology

• _{Shape
and
structure
of
the
network}

“Tree”

Most common in

datacenter. Why?

(6)

Growth

“Star” or

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Growth

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“TradiBonal” Datacenter

40 Servers 40 Servers 40 Servers 40 Servers Edge

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“TradiBonal” Datacenter

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“TradiBonal” Datacenter

AggregaBon Core

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Recall: OversubscripBon

AggregaBon Core

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OversubscripBon

40 Servers 40 Servers 40 Servers 40 Servers Edge AggregaBon Core

All hosts

connected to

same switch.

Full speed

between all of

them. (1:1)

(e.g., 1 Gbps)

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OversubscripBon

AggregaBon Core

If these links are

also 1 Gbps, we

now have 1/40

th

_of

link capacity for

each host. (40:1)

What might we do to

help alleviate this?

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OversubscripBon

AggregaBon Core

10 Gbps gives us

a raBo of 4:1.

Good enough?

Highlighted sub-‐secBon might be OK if:

• ApplicaBon has good locality

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OversubscripBon

AggregaBon Core

Might wants hosts to

have 10 Gbps too!

SBll problemaBc.

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OversubscripBon

AggregaBon Core

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Redundancy (MulB-‐rooted Tree)

AggregaBon Core

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Redundancy (MulB-‐rooted Tree)

AggregaBon Core

Pro: More capacity! Con: Decision must be made (complexity, reordering)

1

?

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Equal-‐Cost MulB Path (ECMP)

• If there’s a decision to be made, hash packet

• All packets of ﬂow (conversaBon) use same path

• Hash collisions lead to poor uBlizaBon

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Paper Preview

• _{“A
Scalable,
Commodity
Data
Center
Network}

Architecture”

– 

AlternaBve tree redundant tree topology design

• _{“Hedera:
Dynamic
Flow
Scheduling
for
Data}

Center Networks”

– 

Use live traﬃc informaBon to decide path choice

• _{“AugmenBng
Data
Center
Networks
with}

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Network Hardware

Tradi&onal Hardware

SDN Hardware

You Can’t read this, it’s too small! Seriously, stop trying to read this, more important things are happening

elsewhere!

elsewhere! You Can’t read this, it’s

too small! Seriously, stop trying to read this, more important things are happening

elsewhere!

LeE Right

This sounds great, why mess with a good thing?

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SoEware-‐Deﬁned Networking (SDN)

Tradi&onal Hardware

SDN Hardware

Controller

elsewhere! You Can’t read this, it’s

too small! Seriously, stop trying to read this, more important things are happening

elsewhere!

LeE @ 100 Mbps Right @ 300 Mbps LeE @ 400 Mbps Right @ 200 Mbps

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Centralized Network Control

• _{Not
so
great
on
the
Internet}

– 

Failures common

– 

Long distances

– 

Who would be in charge?

• _{Powerful
in
controlled
environment}

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Centralized Network Control

• _{Treat
device
as
a
blank
forwarding
table.}

Protocol Src Dst Src_Pt Dst_Pt Output

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Centralized Network Control

• _{Table
built
from
TCAM
memory.}

TCP 10.1.1.1 10.1.1.2 54321 80 1 * 10.1.3.3 10.1.3.4 * * 2

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Centralized Network Control

• _{Table
built
from
TCAM
memory.}

TCP 10.1.1.1 10.1.1.2 54321 80 1 * 10.1.3.3 10.1.3.4 * * 2

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Paper (& Lab) Preview

• _{“Ethane:
Taking
Control
of
the
Enterprise”}

• _{“OpenFlow:
Enabling
InnovaBon
in
Campus}

Networks”

• _{“Extending
Networking
into
the
VirtualizaBon}

Layer”

• _{Lab:
Using
SDN
(OpenFlow)
to
implement}

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Layering

• _{Primary
network
abstracBon:
stack
of
layers}

• _{Each
layer
has
disBnct
responsibiliBes}

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OSI Seven-‐Layer Model

ApplicaBon: the applicaBon (e.g., the Web, Email)

Transport: end-‐to-‐end connecBons, reliability Network: rouBng

Link (data-‐link): framing, error detecBon

Physical: 1’s and 0’s/bits across a medium (copper, the air, ﬁber) PresentaBon: formanng, encoding, encrypBon

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OSI Seven-‐Layer Model

ApplicaBon: the applicaBon (e.g., the Web, Email)

Transport: TCP / UDP Network: IP

Link (data-‐link): Ethernet Physical: Wires

“Layer 7”

“Layer 3”

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Header EncapsulaBon

ApplicaBon Data

Transport: TCP

Network: IP

(payload)

Link: Ethernet

(payload)

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Header EncapsulaBon

ApplicaBon Data

Transport: TCP

Network: IP

(payload)

Link: Ethernet

(payload)

This whole chunk of bytes is what goes out on the wire.

Adds reliability informaBon.

Adds port numbers to

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Header EncapsulaBon

ApplicaBon Data

Transport: TCP

Network: IP

(payload)

Link: Ethernet

(payload)

This whole chunk of bytes is what goes out on the wire.

Adds addresses.

Network: IP address

Link: MAC address

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Addressing

• _{Layer
3
/
Network
/
IP
addresses:}

– 

Hierarchical rouBng

– 

The numerical values say something about the

locaBon of the node in the network

• _{Layer
2
/
Data
Link
/
MAC
addresses:}

– 

Just a ﬂat, unique idenBﬁer

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“Middlebox”

• _{(Usually)
transparent
device
that
looks
at}

traﬃc passing through, someBmes modiﬁes it

• _Examples:

– 

Firewall: Look at traﬃc headers. If the “wrong”

machines are communicaBng, block it.

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CS 91: Cloud Systems & Datacenter Networks Networks Background