17. Mar. 20041INF-3190: Internet Internet Foreleser: Carsten Griwodz Email: [email protected]@ifi.uio.no

17. Mar. 2004 1 INF-3190: Internet

Internet

Foreleser: Carsten GriwodzEmail: [email protected]


Multicast


Multicast Multicast Definition

Unicast: 1:1 communication Multicast: 1:n communication

Tasks To send data to a group of end

systems one-time sending instead of multiple sending

To maintain the overall load at a low level

Results Lower network load Lower load on the sender

Condition: group addressing Group membership may change,

managed for example by

Sender

Receiver

Receiver

Receiver

Sender

Receiver

Receiver

Receiver


Internet Multicast• Multicast

• Means to create trees, to address them, to modify them ...

• IP Multicast Model• Shared Tree

• tree may be used by several senders• Source Tree

• tree is used by exactly one sender

• Properties / Fields of Activity / Topics• Group addressing• Routing• Reliable multicast

• temporally limited and error free


IP Multicast: Concepts• Virtual Overlay Network

• isolated solutions capable of multicasting• connected worldwide through several tunnels• logical tree structure

• Dynamic, anonymous group model• no restrictions regarding the participants

(location/number)• dynamic group membership• one host may be a member of several groups at the

same time• sender does not have to be a member of the group• no restrictions regarding the group’s duration


IP Multicast• Addresses

• IPv4• 28 bit, i. e. > 250 Mio.

Groups• IPv6

• 120 bit

• Types of group addresses• Permanent

• e. g. all ES and IS on one LAN,

• all IS (router) on one LAN, ...

• Temporary

• Internet Group Management Protocol (IGMP)

• RFC 1112• dynamic definition of

group memberships

0 Network Host

1

7

0

1 1 0

Network Host

Network Host

1 1 01 Multicast address

1 111 Reserved

24

14 16

21 8

28

28

0000 0001…

1111 1110 101111 1110 111111 1111

Unassigned…

Link local use addressesSite local use address

Multicast

0000 0000 Reserved (including IPv4) 1/256

…

1/1024

1/256

1/256

1/1024

Prefix (binary) Usage Fraction


IP Multicast Scoping rules

Two ways of limiting multicast group size TTL scoping Administrative scoping

TTL scoping Original, first used in MBone Limits distribution based on TTL field

Administrative scoping Set of RFCs Limits distribution based on addresses


IP Multicast TTL scoping

IPv4 scoping style Introduced for the Multicast backbone Not covered by RFCs Still in use

16 - Country

TTL Do not forward outside …

32 - Continent64 - World-wide

128 - Low bandwidth tunnels

1 - 15 Organization


IP Multicast Address Assignment Multicast address grouping in IPv4

1 1 01 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 x x x x x x x x

8 8 8 8

Local Network Control Block

Internetwork Control Block

Ad-Hoc Control Block

ST Multicast Groups

SDP/SAP Block

DIS Transient Block

reserved

Source Specific Multicast Block

GLOP Block

Administratively Scoped Block

1 1 01 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 x x x x x x x x

1 1 01 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0

1 1 01 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

1 1 01 0 0 0 0 0 0 0 0 0 0 0 1 x x x x x x x x x x x x x x x x

1 1 01 0 0 0 0 0 0 0 0 0 0 1 0 x x x x x x x x x x x x x x x x

1 1 01 0 0 0 0 1 1 1 1 1 1 x x x x x x x x x x x x x x x x x x

1 1 01 0 0 0 1 x x x x x x x x x x x x x x x x x x x x x x x x



1 1 01 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1 1 01 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1reserved




Local network control block For control traffic in one LAN

Internetwork control block For control traffic forwarded through the entire Internet

Ad-hoc control block First-come first-serve

ST multicast groups Used by ST-II (the connection-oriented network layer

protocol with version number 5)

SDP/SAP block Exclusively for SAP messages



DIS transient block Historical – may be reassigned

Source specific multicast block No allocation required Routers must build one tree per (source IP address, multicast

destination address)

GLOP block Addresses that can be requested using a global allocation

mechanism Multicast address dynamic client allocation protocol

(MADCAP) Addresses are requested for some time

Administratively scoped block Like administrative scoping in IPv6, next slide


IP Multicast Address Assignment Administrative scoping in IPv6

scop is a 4-bit multicast scope value used to limit the scope of the multicast group

8flags Group ID1 1 1 1 1 1 1 1 scop

4 4 112

0 0 0 T

0scop

123456789ABCDEF

reservedInterface-local scopeLink-local scope

Admin-local scopeSite-local scope

reserved

Organization-local scope

Global scopereserved

(unassigned)(unassigned)

(unassigned)

(unassigned)

(unassigned)(unassigned)(unassigned)

meaning

T=0 Permanently assigned

(“well-known”) multicast address, assigned by IANA (Internet Assigned Number Authority)

T=1 Non-permanently

assigned (“transient”) address


IP Multicast Address Assignment Administrative scoping in IPv4

Interface-local Only inside one machine

Link-local Only inside a single LAN or on one point-to-point

connection Admin-local

Smallest scope that can not be automatically configured Site-local

Inside one site Where all nodes have the same subnet ID

Organization-local Multiple sites of one organization

Global


IP Multicast Address Assignment Unicast-prefix scoping in IPv6

8flags1 1 1 1 1 1 1 1 reserved

4 4

0 0 1 1

flags Must be 0011

scop As before

scop8

plen8

network prefix64 32

group id

plen Number of bits used for

network prefix network prefix

Identifies the prefix of a subnet

group id A multicast group id that

is unique for the subnet


Multicast Routing


Spanning Tree

Principle Global knowledge of the multicast group’s spanning tree

(Multicast Tree), Initially only local knowledge

Distribution of Information First IS adapts spanning tree to the specific group

i.e. aligning (propagating) the spanning tree by distance vector routing or link state routing

22

2

22

11

1 1

1Multicast source IS

Spanning tree for source IS

Spanning tree for group 2

Spanning tree for group 1


Spanning Tree Principle

all IS must know the multicast tree i.e. each IS

knows to which group it belongs but does not know (initially) which other IS belong to

the group as well distribution of this information

depends on the underlying routing protocol here: Link State Routing


Spanning Tree with Link State Routing

Link State Routing All IS send link state packets periodically

Containing information distance to neighbours expanded by information on multicast group

By broadcast to all the others Each IS calculates a multicast tree

From the now locally available and complete state information

Based on the information about the multicast tree

IS determines the outgoing lineson which packets have to be transmitted


Reverse Path Forwarding with Pruning

Pruning Feedback in order to stop data transfer Feedback is generated by IS without interested

end systems

Principle Sender sends first multicast packet to

everybody, using the broadcast method Reverse Path Forwarding

Then apply adaptation (Pruning) Because broadcasting too resource consuming



Reverse Path Forwarding When a multicast packet arrives at an IS

from origin S on an interface I

Test whether it would send unicast packets to S via I Yes

Deliver multicast packet to all connected end systems in the multicast group(they must have registered themselves using IGMP)

Forward multicast packet on all interfaces to other routers except I

No Drop packet (assume it’s a duplicate)



Pruning When a multicast packet arrives from S on interface I If

No directly connected end system is registered Non-Membership-Reports (NMRs) are received from all IS

reachable via interfaces other than I Then

Send a Non-Membership-Report (NMR) to the previous IS that forwarded the packet

Do not forward messages for the group any more

Flooding and pruning must be repeated after some time To find end-systems that have joined

Benefit Pruning only on trees that are actually used Unused trees are cut coarsely

Optimized for many receivers


Core-Based Tree

Also known as "Trees with Rendezvous Points“ Principle

the core is selected (an IS which is central to the group) the group’s spanning tree from this node/IS is determined the sender transmits a packet to this central IS the core transmits this packet via the spanning tree

Properties+ simple central calculation+ one tree common to all n senders (instead of n trees)- route to the central IS may not be optimized

Core IS

Non-Core IS


Truncated Reverse Path Forwarding Principle

Enhancement of broadcast routing approach"Reverse-Path-Broadcast“


Reverse Path Broadcast Motivation

When packets are forwarded,they are forwarded over all edges (not including the incoming one)

Better if over only one suitable edge

Algorithm: packet from source S to destination Has packet arrived via an IS entry over which packets

may also be sent to station/source S? Yes

Packet used the best route until now Select the edges at which the packets arrived that were

routed to S Forward over those edges

No Discard packet (is most likely a duplicate)


Reverse Path Broadcast

In the example A can learn by inspecting the unicast packets

that it is located on the unicast path from B to S X can learn by packets failing to appear

that it is not located on the unicast path from B to S This information is used by the RPB algorithm

Broadcast Sender S

EF

X

B

A

C

D

8

2 1

2

1

3

3

2

3

UnicastPath


Reverse Path Broadcast

In the example with the RPB algorithm X does not forward a broadcast packet from S to B, because X

knows that B does not receive unicast packets via X but sends them over a different node instead with this other node then receiving the broadcast packet

Broadcast Sender S

EX

B

A

C

D

8

21

2

1

3

3

2

3

XX

X

XX no transmission of broadcast

packets into this direction, becausethe opposing party does not sendpackets to S over this channel.


Truncated Reverse Path Forwarding Principle

Enhancement of broadcast routing approach"Reverse-Path-Broadcast“

Here packets are sent only on edge/leaf links which Contain group members Contain additional routers in their path (known from the message

exchange between the routers)

Algorithm (when packet arriving at IS) Has this packet arrived from the same connection over which

packets are sent to this station? Yes

Packet used the most favorable route up to now Select all subnetwork edges/leaf links (not incl. the incoming one) that

Contain group members, or Contain additional routes within their path

Forward over those edges No

discard packet (is probably duplicate)


Truncated Reverse Path Forwarding Comment on selecting the outgoing paths

Recognizing leaf links by sending router messages Exchange membership information via IGMP Uncoupling of subnetworks only (no pruning procedure)


Additional Procedures & Topics Additional Variations

Steiner Trees (optimizing network resources) Distance Vector Multicast Routing Protocol (DVMRP)

Flooding and pruning approach Hierarchic DVMRP

Two-tiered, non-overlapping domains/subnetworks Multicast Open Shortest Path First (MOSPF)

Based on link state routing OSPF Protocol Independent Multicast – Dense Mode (PIM-DM)

Similar to DVMRP Protocol Independent Multicast – Sparse Mode (PIM-SM)

For groups with small spatial density Related to core-based trees


Additional Procedures & Topics Objectives

Optimizations Constraints

Optimizations Edge optimization

e. g. path with largest bandwidth Path optimization

e. g. path with the lowest overall costs

Constraints Edge limited

e. g. find a path that adheres to the constraints at every edge Path limited

e. g. path which does not exceed a certain overall delay


Mobile IP


Mobile IP Motivation

Networked society demands for & enables mobility at work private environment

Infrastructure: wireless communication technologies spreading more and more e.g. hotspots with IEEE 802.11

End systems: laptops, palmtops are getting more and more powerful

Mobility using Internet technology

Mobile IP Adds mobility to the Internet History

developed by the Internet Engineering Task Force (IETF) proposed standard in 1996 (RFC 2002) obsoleted by RFC3344

There are many more RFCs and drafts in this area, seehttp://www.ietf.org/html.charters/mobileip-charter.html


Problems & Challenges IP address of end system

Belong to organizational entity Contains topological information

Intermediate systems Use the IP address for routing definition

Network information, or Subnet information (part of host-Id), or Only end system information (part of host-Id)

Change of physical subnet implies Either: Change of IP address Or: Change entries in routing tables

Problems How to connect mobile end system to the Internet?

With existing address but from a different location Routing to mobile end system does not work Changing IP address

DNS updates take to long time TCP connections break

Changing entries in routing tables Does not scale with the number of mobile hosts and frequent changes in the

location


Problems & Challenges with Mobility in the Internet

(simple) Possible solutions

Use new IP address at each respective location Information of own IP address maintained at many locations

(e.g. DNS), update impractical, problems with IPSec

Communication with other systems has to be interrupted when changing location

Modified routing definitioni.e. routers to make use of complete IP address

Router tables with millions of entries, extremely high costsSecurity problems

(secure change of routes)


Requirements Basic requirement

Mobile end system uses the same IP address allover Transparency

Compatibility requirements No modifications on existing

(non-mobile) end system necessary IS (i.e. routers)

Tables Protocols

Interoperability with TCP/IP protocol-suite Possibility to adapt existing applications Solution should be independent

from an underlying wireless network technology


Requirements Performance requirements

No overhead with mobile end system in stationary cases

Should have solid scaling characteristics Quantity of administrative protocol messages

should be low because often lower bandwidth of wireless networks limited battery performance of mobile end system

Security requirements E.g. all registration messages have to be

protected


Components

Mobile Node (MN), mobile host moves to different location uses permanent IP address

Correspondend Node (CN) Communication partner to mobile node

Home Agent (HA) IS (router) in the home network of the mobile host

knows the mobile hosts, which are not "at home" at the moment knows the current location of the mobile host tunnels IP packets (re-routes them) to the mobile host’s location

Home LAN

Home agentCell

Mobile host

Foreign LANWAN Correspondent node


Components

Foreign Agent (FA) IS (router) in the foreign network

mobile hosts log on to the foreign agents unpacks tunneled IP packets re-routes them to their respective mobile host assigns addresses (CoA) to the visiting Mobile Node

Care-of-Address (CoA) Tunnel endpoint of the Mobile Node while abroad

Home LAN

Home agentCell

Mobile host

Foreign agent



Protocol Overview

A mobile host moves to a foreign network1. The foreign agent periodically sends out agent

advertisements thereby the mobile host receives a care-of-address

care-of-address is used to inform the home agent of the new location

2. The home agent intercepts and redirects the IP packets which are intended for the mobile host to its new address

this is done by means of an IP tunnel 3. Once the mobile host is back in its home network

it de-registers from its home agent

Home LAN

Home agentCell

Mobile host

Foreign agent



Protocol Overview

The mobile IP protocol consists out of three independent functions

Agent discovery Registration Tunneling

Home LAN

Home agentCell

Mobile host

Foreign agent



Agent Discovery Procedure used by the mobile host to determine if

it is in its home network it is in a foreign network it has moved into another (additional) foreign network (move

detection)

Message type: Agent Advertisements transmitted by home or foreign agent

to offer their services to mobile hosts determines in which network the mobile host is

if it is in a foreign network it receives a care-of-address from Agent Advertisement

Message type: Agent Solicitations transmitted from the mobile host

if it cannot/does not want to wait any longer for the agent advertisement


Agent Discovery The care-of-address is

temporary IP address for the mobile host specific for the foreign network defines the location of the mobile host i.e. it is the IP address transmitted to the home agent and to

which the IP packets, which are intended for the mobile host, are re-routed


Registration

Foreignagent

Mobilehost

Requestsservice

Homeagent

WANWAN

FA relays requestto HA

HA acceptsor denies

FA relaysStatus to MH

Agent discovery(incl. advertisements)


Registration Main purpose

to transmit the new care-of-address of the mobile host to the home agent

Home agent logs the current care-of-addresses in a table each registration has a period of validity

The mobile host registers itself when it is in a new network when the old registration expires

Note authentications of registration messages done using the MD5

algorithm


Tunneling

Foreign agent

Correspondentnode

Home agent

Packet issent to the mobilehost’s home address

Packet is tunneledto the foreign agent


Tunneling IP packets of the correspondent node to the mobile host

are routed to the home agent

Home agent performs IP-in-IP Encapsulation original packets are "encapsulated" into surrounding IP

packets destination is current care-of-address IP packet is routed to the care-of-address this process is called Tunneling

The foreign agent is the finishing point of the tunnel unpacks the packet transfers it to the mobile host according to the original home

address


A Few Additional Aspects

Foreign agent

Correspondentnode

Home agent

Packet issent to the mobilehost’s home address

Packet is tunneledto the foreign agent

Sender is given foreign agents address

Tunnel to theforeign agent


A Few Additional Aspects Redirecting the packets from the mobile host to the

correspondent host can be sent directly to the correspondent host

by using the care-of-address as the sender’s address or, for security reasons, be done

by means of reverse tunneling i.e. the packets are "re-tunneled" to the home agent note: route optimization

If no foreign agent is available, a mobile host itself can assume this function

the mobile host gets a colocated care-of-address from a foreign network,

e.g. via the "Dynamic Host Configuration Protocol" (DHCP) this address is then used exclusively by the mobile host it transmits this address to its home agent and represents the tunnel’s finishing point


Mobile IP: Problems Without special care

Reverse tunneling may be necessary for Firewalls Streaming servers with destination check

Mandatory in RTSP Tunneling

IP in IP has an additional header Reduces the max MTU size

Large increase in delay End-to-end distance IP in IP processing

Increase in jitter and loss No reasonable interaction

With multicast Subscribe to groups through the tunnel

With reservation protocols E.g. RSVP relies on multicast

Documents

17. Mar. 20041INF-3190: Internet Internet Foreleser: Carsten Griwodz Email: [email protected]@ifi.uio.no