Network Layer Part A (IPv6) Network Layer 4-1 Chapter 4: outline - - PowerPoint PPT Presentation

Network Layer – Part A (IPv6)

Network Layer 4-1

4.1 Overview of Network layer

• data plane
• control plane

4.2 What’s inside a router 4.3 IP: Internet Protocol

• datagram format
• fragmentation
• IPv4 addressing
• network address

translation

• IPv6

4.4 Generalized Forward and SDN

• match
• action
• OpenFlow examples
• f match-plus-action in

action

Chapter 4: outline

4-2 Network Layer: Data Plane

Network Layer 4-3

IPv6: motivation

 initial motivation: 32-bit address space soon to be

completely allocated.

 additional motivation:

• header format helps speed processing/forwarding
• header changes to facilitate QoS

IPv6 datagram format:

• fixed-length 40 byte header
• no fragmentation allowed

IPv6 Design Issues

 Overcome IPv4 scaling problem

• lack of address space.

 Flexible transition mechanism.  New routing capabilities.  Quality of service.  Security.  Ability to add features in the future.

Size of the Internet

Network Layer 5

1000 2000 3000 4000 5000 6000 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Theoretical Usable Allocated Addressable

IPv4 Doomsday ?

Distribution Statement A: Cleared for Public Release; Distribution is unlimited.

Internet BGP Routing Table

Network Layer 6

Exponential Growth No Growth Linear Growth CIDR deployment Exponential Growth - CIDR breaking down

http://www.telstra.net/ops/bgptable.html

Distribution Statement A: Cleared for Public Release; Distribution is unlimited.

Network Layer 7

Network Layer 8

Network Layer 9

What about technologies & efforts to slow the consumption rate?

 Dial-access / PPP / DHCP

• Provides temporary allocation aligned with actual endpoint use.

 Strict allocation policies

• Reduced allocation rates by policy of ‘current-need’ vs. previous

policy based on ‘projected-maximum-size’.

 CIDR

• Aligns routing table size with needs-based address allocation policy.

Additional enforced aggregation actually lowered routing table growth rate to linear for a few years.

 NAT

• Hides many nodes behind limited set of public addresses.

Network Layer 10

What were the benefits?

 Actual allocation history

• 1981 – IPv4 protocol published
• 1985 ~ 1/16 total space
• 1990 ~ 1/8 total space
• 1995 ~ 1/4 total space
• 2000 ~ 1/2 total space

 The lifetime-extending efforts & technologies delivered the

ability to absorb the dramatic growth in consumer demand during the late 90’s. In short they bought – TIME –

Network Layer 11

Would increased use of NATs be adequate?

NO!

 NAT enforces a ‘client-server’ application model where the server has

topological constraints.

• They won’t work for peer-to-peer or devices that are “called” by others

(e.g., IP phones)

• They inhibit deployment of new applications and services, because all NATs

in the path have to be upgraded BEFORE the application can be deployed.

 NAT compromises the performance, robustness, and security of the

Internet.

 NAT increases complexity and reduces manageability of the local

network.

 Public address consumption is still rising even with current NAT

deployments.

Network Layer 12

IPv6 Background

 IP has been patched (subnets, supernets) but there is

still the fundamental 32 bit address limitation

 IETF started effort to specify new version of IP in 1991

• New version would require change of header
• Include all modifications in one new protocol
• Solicitation of suggestions from community
• Result was IPng which became IPv6
• First version completed in ’94

 Same architectural principles as v4 – only bigger

Network Layer 13

What Ever Happened to IPv5?

IP March 1977 version (deprecated) 1 IP January 1978 version (deprecated) 2 IP February 1978 version A (deprecated) 3 IP February 1978 version B (deprecated) 4 IPv4 September 1981 version (current widespread) 5 ST Stream Transport (not a new IP, little use) 6 IPv6 December 1998 version (formerly SIP, SIPP) 7 CATNIP IPng evaluation (formerly TP/IX; deprecated) 8 Pip IPng evaluation (deprecated) 9 TUBA IPng evaluation (deprecated) 10-15 unassigned

Network Layer 14

IPv6 RFCs

 1752 - Recommendations for the IP Next Generation

Protocol

 2460 - Overall specification  2373 - addressing structure  others (find them)  www.rfc-editor.org

Network Layer 15

What were the goals of a new IP design?

 Expectation of a resurgence of “always-on” technologies

• xDSL, cable, Ethernet-to-the-home, Cell-phones, etc.

 Expectation of new users with multiple devices.

• China, India, etc. as new growth
• Consumer appliances as network devices

– (1015 endpoints)

 Expectation of millions of new networks.

• Expanded competition and structured delegation.

– (1012 sites)

Network Layer 16

Benefits of 128 bit Addresses

 Room for many levels of structured hierarchy and routing

aggregation

 Easy address auto-configuration  Easier address management and delegation than IPv4  Ability to deploy end-to-end IPsec

(NATs removed as unnecessary)

Network Layer 17

Incidental Benefits of New Deployment

 Chance to eliminate some complexity in IP header

• improve per-hop processing

 Chance to upgrade functionality

• multicast, QoS, mobility

 Chance to include new features

• binding updates

Network Layer 18

IPv6 Enhancements (1)

 Expanded address space

• 128 bit

 Improved option mechanism

• Separate optional headers between IPv6 header and

transport layer header

• Most are not examined by intermediate routes
• Improved speed and simplified router processing
• Easier to extend options

 Address autoconfiguration

• Dynamic assignment of addresses

Network Layer 19

IPv6 Enhancements (2)

 Increased addressing flexibility

• Anycast - delivered to one of a set of nodes
• Improved scalability of multicast addresses

 Support for resource allocation

• Replaces type of service
• Labeling of packets to particular traffic flow
• Allows special handling
• e.g. real time video

Network Layer 20

Summary of Main IPv6 Benefits

 Expanded addressing capabilities  Structured hierarchy to manage routing table growth  Serverless autoconfiguration and reconfiguration  Streamlined header format and flow identification  Improved support for options / extensions

Network Layer 21

Address Complexity

 IPv6 actually has many kinds of addresses

• unicast, anycast, multicast,
• link-local, site-local, loopback, IPv4-embedded, care-of,

manually-assigned, DHCP-assigned, self-assigned, solicited-node, and more…

 most of this complexity is also present in IPv4,

just never written down in one place

• a result of 20 years of protocol evolution

 one simplification: no broadcast addresses in IPv6!

• uses multicast to achieve same effects

Network Layer 22

Types of address

 Unicast

• Single interface

 Anycast

• Set of interfaces (typically different nodes)
• Delivered to any one interface
• the “nearest”

 Multicast

• Set of interfaces
• Delivered to all interfaces identified

Network Layer 23

IPv6 Addresses

 128 bits - written as eight 16-bit hex numbers.

5f1b:df00:ce3e:e200:0020:0800:2078:e3e3

 High order bits determine the type of address.

The book shows the breakdown of address types.

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Network Layer

Unicast Assignment in v6

 Unicast address assignment is similar to CIDR

• Unicast addresses start with 001
• Host interfaces belong to subnets
• Addresses are composed of a subnet prefix and a host identifier
• Subnet prefix structure provides for aggregation into larger networks

 Provider-based plan

• Idea is that the Internet is global hierarchy of network
• Three levels of hierarchy – region, provider, subscriber
• Goal is to provide route aggregation to reduce BGP overhead
• A provider can advertise a single prefix for all of its subscribers
• Region = 13 bits, Provider = 24 bits, Subscriber = 16 bits, Host = 80 bits
• Eg. 001,regionID,providerID,subscriberID,subnetID,intefaceID
• What about multi-homed subscribers?
• No simple solution

 Anycase addresses are treated just like unicast addresses

• It’s up to the routing system to determine which server is “closest”

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IPv6 Addressing

 Classless addressing/routing (similar to CIDR)  Notation: x:x:x:x:x:x:x:x (x = 16-bit hex number)

• contiguous 0s are compressed: 47CD::A456:0124
• IPv6 compatible IPv4 address: ::128.42.1.87

 Address assignment

• provider-based (can’t change provider easily)
• geographic

Network Layer 26

001 Registry ID Provider ID Subscriber ID Subnet ID Interface ID n bits m bits

• bits

p bits (125-m-n-o-p) bits

IPv6 Addressing

 Top Level and Next Level Aggregators  Interface ID typically from MAC address  Special site-local and link-local addresses  Special multicast and anycast addresses  Special IPv4 compatible addresses TLA NLA SLA Interface ID resv 3 13 8 24 16 64 F Public Topology Site Topology

IPv4-Mapped IPv6 Address

 IPv4-Mapped addresses allow a host that support

both IPv4 and IPv6 to communicate with a host that supports only IPv4.

 The IPv6 address is based completely on the IPv4

address.

28

Network Layer

IPv4-Mapped IPv6 Address

 80 bits of 0s followed by 16 bits of ones, followed

by a 32 bit IPv4 Address:

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0000 . . . 0000 IPv4 Address FFFF 80 bits 32 bits 16 bits

Works with DNS

 An IPv6 application asks DNS for the address of a

host, but the host only has an IPv4 address.

 DNS creates the IPv4-Mapped IPv6 address

automatically.

 Kernel understands this is a special address and

really uses IPv4 communication.

30

Address Autoconfigure

 Start with link-local address  Neighbor Discovery (ND) multicast to find prefix

• r DHCP server

 Stateful assignment via DHCPv6  Stateless assignment via a routing prefix  Entire sites can renumber with new prefix  Mobility via dynamic care-of address

Address Space and Notation

 Allocation is classless

• Prefixes specify different uses (unicast, multicast, anycast)
• Anycast: send packets to nearest member of a group
• Prefixes can be used to map v4 to v6 space and visa-versa
• Lots of flexibility with 128 bits!
• ~1500 address/sqft of the earths surface

 Standard representation is set of eight 16-bit values separated by

colons

• Eg. 47CD:1234:3200:0000:0000:4325:B792:0428
• If there are large number of zeros, they can be omitted with series of

colons

• Eg. 47CD:1234:3200::4325:B792:0428
• Address prefixes (slash notation) are the same as v4
• Eg. FEDC:BA98:7600::/40 describes a 40 bit prefix

32

Address Prefix Assignments

33

0000 0000 Reserved 0000 0001 Unassigned 0000 001 Reserved for NSAP (non-IP addresses used by ISO) 0000 010 Reserved for IPX (non-IP addresses used by IPX) 0000 011 Unassigned 0000 1 Unassigned 0001 Unassigned 001 Unicast Address Space 010 Unassigned 011 Unassigned 100 Unassigned 101 Unassigned 110 Unassigned 1110 Unassigned 1111 0 Unassigned 1111 10 Unassigned 1111 110 Unassigned 1111 1110 0 Unassigned 1111 1110 10 Link Local Use addresses 1111 1110 11 Site Local Use addresses 1111 1111 Multicast addresses

IP Options

IPv4 and IPv6

Vers 4

IHL

Type of Service

Total Length Identification

Flags

Frag Offset

Time to Live

Protocol Header Checksum Source Address Destination Address Source Address Destination Address Payload Length Hop Limit Next Hdr Flow Label

Traffic Class Vers 6

v4 Header = 20 Bytes + Options v6 Header = 40 Bytes

IPv6 Headers

 Simpler header - faster processing by routers.

• No optional fields - fixed size (40 bytes)
• No fragmentation fields.
• No checksum

 Support for multiple headers

• more flexible than simple “protocol” field.

35

IPv6 Header Fields

 VERS: 6 (IP version number)  Priority: will be used in congestion control  Flow Label: experimental - sender can label a

sequence of packets as being in the same flow.

 Payload Length: number of bytes in everything

following the 40 byte header, or 0 for a Jumbogram.

36

IPv6 Header Fields

 Next Header is similar to the IPv4 “protocol”

field - indicates what type of header follows the IPv6 header.

 Hop Limit is similar to the IPv4 TTL field (but

now it really means hops, not time).

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Key differences in header

 No checksum

• Bit level errors are checked for all over the place

 No length variability in header

• Fixed format speeds processing

 No more fragmentation and reassembly in header

• Incorrectly sized packets are dropped and message is

sent to sender to reduce packet size

• Hosts should do path MTU discovery
• But of course we have to be able to segment packets!
• What about UDP packets?

38

Extension Headers

IPv6 extension headers.

Network Layer 39

5-69

Figure 3.4

Network Layer 40 Stallings HSNET 2ed

Extension Headers (2)

Daisy Chain extension Headers

Network Layer 4-41

Basic header Next header = TCP TCP segment Basic header Next header = routing Routing header Next header = fragment Fragment header Next header = authentication TCP segment Authentication header Next header = TCP

Extension Headers (3)

Network Layer 42 Stallings HSNET 2ed

Extension Headers (4)

The hop-by-hop extension header for large datagrams (jumbograms).

Network Layer 43

Hop-by-Hop Options

 Next header  Header extension length  Options

• Pad1
• Insert one byte of padding into Options area of header
• PadN
• Insert N (2) bytes of padding into Options area of header
• Ensure header is multiple of 8 bytes
• Jumbo payload
• Over 216 = 65,535 octets
• Router alert
• Tells router that contents of packet is of interest to router
• Provides support for RSPV (chapter 16)

Network Layer 44

Fragmentation Extension

 Similar to v4 fragmentation

• Implemented as an extension header
• Placed between v6 header and data (if it is the only extension used)
• 13 bit offset
• Last-fragment mark (M)
• Larger fragment ID field than v4

 Fragmentation is done on end host  Node must perform path discovery to find smallest MTU of

intermediate networks

• Source fragments to match MTU
• Otherwise limit to 1280 octets

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next header reserved

• ffset

M reserved ID

Routing

 Same “longest-prefix match” routing as IPv4 CIDR  Straightforward changes to existing IPv4 routing protocols to

handle bigger addresses

• unicast: OSPF, RIP-II, IS-IS, BGP4+, …
• multicast: MOSPF, PIM, …

 Use of Routing header with anycast addresses allows routing

packets through particular regions

 List of one or more intermediate nodes to be visited

• e.g., for provider selection, policy, performance, etc.

Network Layer 46

Routing Extension

 Without this header, routing is essentially the same as v4  With this header essentially same as the source routing option in v4

• Loose or strict

 Header length is in 64-bit words  Up to 24 addresses can be included

• Packet will go to nearest of these in “anycast” configuration

 Segments left tracks current target

47

8 16 24 31 Next header

• Hd. Ext. Len

Segmnts left 1 – 24 addresses

Routing Header

The extension header for routing.

Network Layer 48

Reserved Strict/Loose Bit Mask Address 1 Address 2 0 8 16 24 31 Next Header Header Length Routing Type = 0 Segment Left

. . .

Address 24

Example of Using the Routing Header

Network Layer 49

S A B D

Example of Using the Routing Header

Network Layer 4-50

S A B D

Example of Using the Routing Header

Network Layer 4-51

S A B D

Example of Using the Routing Header

Network Layer 52

S A B D

Network Layer 4-53

Transition from IPv4 to IPv6

 not all routers can be upgraded simultaneously

• no “flag days”
• how will network operate with mixed IPv4 and

IPv6 routers?

 tunneling: IPv6 datagram carried as payload in IPv4

datagram among IPv4 routers

IPv4 source, dest addr IPv4 header fields

IPv4 datagram IPv6 datagram

IPv4 payload UDP/TCP payload IPv6 source dest addr IPv6 header fields

Network Layer 4-54

Tunneling

physical view:

IPv4 IPv4

A B

IPv6 IPv6

E

IPv6 IPv6

F C D logical view:

IPv4 tunnel connecting IPv6 routers

E

IPv6 IPv6

F A B

IPv6 IPv6

Network Layer 4-55

flow: X src: A dest: F data

A-to-B: IPv6

Flow: X Src: A Dest: F data

src:B dest: E

B-to-C: IPv6 inside IPv4 E-to-F: IPv6

flow: X src: A dest: F data

B-to-C: IPv6 inside IPv4

Flow: X Src: A Dest: F data

src:B dest: E physical view: A B

IPv6 IPv6

E

IPv6 IPv6

F C D logical view:

IPv4 tunnel connecting IPv6 routers

E

IPv6 IPv6

F A B

IPv6 IPv6

Tunneling

IPv4 IPv4