Fabric: A Retrospective on Evolving SDN

thoughtlessskytopNetworking and Communications

Oct 29, 2013 (3 years and 11 months ago)

91 views

Author :
Martín
Casado
,

Teemu

Koponen
,

Scott
Shenker
,

Amin
Tootoonchian

Publisher :

Presenter : Pei
-
Hua

Huang

Date : 2013/10/02


Fabric: A Retrospective on Evolving
SDN

Introduction


Current networks
are
too expensive
, too complicated to
manage, too prone to
vendor
-
lockin
, and
too hard to
change


Network infrastructure
has two components:

(i)
the underlying hardware

(ii)
the
software that controls the overall
behavior of
the network

1

Introduction


Ideal hardware :

Simple
:

inexpensive to build
and operate

Vendor
-
neutral
:
easy to switch between
hardware
vendors

Future
-
proof
:
as
much as
possible to accommodate
future
innovation


Ideal software
:

Flexible
: should support
the wide variety of
requirements

2

Background


Network infrastructure design is guided by network
requirements and
network
interfaces


Network requirements come from
two sources:

(i)
Host :
want their packets to travel to a particular
destination

(ii) Network operator : traffic engineering,


virtualization
, tunneling and isolation

3


There are
three relevant
interfaces

(i)
Host
-
Network
: inform the network of host’s
requirements

(ii)
Operator
-
Network

: inform the network of operator’s
requirements

(iii)
Packet
-
Switch

: identify packet to a switch

4

Original Internet


The goal is to
merely carry the packet
from source
to
destination


Every router
would independently interpret
the host
requirements and take the
appropriate
forwarding
action


Host
-
Network and Packet
-
Switch interfaces were identical,
and no Operator
-
Network
interface

5

MPLS


MPLS introduced an explicit distinction between the
network
edge and
the network
core


Edge routers inspect the incoming
packet headers

and then
attach a label onto the
packet

which is used
for all
forwarding
within the
core


Distinguished Host
-
Network
and Packet
-
Switch interfaces,
but
no Operator
-
Network
interface

6

SDN


provide
a fully programmatic
Operator
-
Network interface


In
OpenFlow

each switch within the network exports an
interface that
allows a remote controller to manage its
forwarding
state


do
not
distinguish between
the Host
-
Network interface and
the Packet
-
Switch interface

7

SDN


three
problems

(i)
no simplified hardware

(ii)
no sufficient flexibility

(iii)
it
unnecessarily couples the host requirements to
the
network
core behavior

8

Extending SDN


9

Extending SDN


the
key properties for fabrics

(i)
Separation
of
Forwarding
:


external addresses are not used
in forwarding
decisions

within
the fabric both

to
simplify the
fabric forwarding

elements
,
but
also to allow for independent
evolution of

fabric
and
edge

(i)
Separation
of
Control
:


Separating
the control
planes allows them
each
to

evolve
separately, focusing
on the specifics
of the

problem

10

Fabric Service Model


a
fabric should
be able to support any number of edge
designs
including different
addressing schemes and policy
models

11

Fabric Path Setup


two methods
are commonly
used
today

1.
use a standard IGP (like OSPF) and ECMP to build a
fabric

2.
MPLS, requires
the explicit provisioning of an LSP
by the
provider

12

Addressing and Forwarding in the Fabric


A forwarding
element in the
fabric is not
required to use
end
-
host addresses for
forwarding,
they are only responsible
for delivering a packet
to its
destination(s
)


Two approaches
can be
optimized the implementation
of the
fabric
forwarding

1.
follow
MPLS

2.
limit the packet operations to
a destination
address lookup
with a longest prefix match
with ECMP
-
based
forwarding

13

Mapping the Edge Context to the Fabric


The complexity in an edge/fabric architecture lies in
mapping the edge context to network addresses or paths


two primary mechanisms

1.
Address translation
: swapping out addresses in situ

2.
Encapsulation



14

Questions and Implications


Isn’t this just another approach to layering
?


What does this mean for
OpenFlow
?


Why is simplicity so important?


What does this mean for networking more generally?


15