Transcript pptx - SFU computer science

CMPT 471
Networking II
Multicasting
© Janice Regan, 2006-2013
1
Types of Multicasting (1)
 Multicasting is useful in several contexts
(RFC
3569)
 SSM, source specific multicast: Information
is sent to all members of the multicast group
from a single source , members do not
communicate directly with each other.


Multimedia “broadcast” to many destinations
(hosts and networks)
Multicast to hosts on a local network for resource
discovery
© Janice Regan, 2006-2013
2
Types of Multicasting (2)
 Multicasting is useful in several contexts
(RFC 3569)
 ASM, any source multicast: many sources and many
destinations, no limit on source or number of hosts







Supports applications such asTeleconferencing, gaming, and
distributed computing
An IP datagram is transmitted to a "host group“
A “host group” is a set of >=0 end-hosts (or routers) identified by
a single IP destination address (224.0.0.0 - 239.255.255.255 ).
End-hosts may join and leave the group any time,
Any host may send to a group
Only members of the group may receive from that group
protocols include ICMPv2 with DVRMP (or PIM or MOSPF)
© Janice Regan, 2006-2013
3
Types of Multicasting (3)
 Multicasting is useful in several contexts
(RFC
3569)
 SFM, source filtered multicast can specify
one type of filtering either


INCLUDE: Specify the group and the members of the
group from which incoming data will be accepted,
EXCLUDE: Specify hosts from which multicast data will not
be accepted
 A variant of ASM (using IGMPv3 for IPv4 and
MLDv2 for IPv6) with source filtering added
© Janice Regan, 2006-2013
4
ASM Multicasting Overview
 Transmit to a group of hosts on several networks.
 This group of hosts includes a subset of hosts on each




of the several networks. (subset may be entire network)
Membership in the group is dynamic. Hosts may join or
leave groups as they wish.
A multicast router (mrouted, pimd) used to route
between networks with members in a multicast group
It is the responsibility of the multicast router to monitor
and update changes in membership of groups, both
within and outside the attached networks
A single multicast address in the range (224.0.0.0 –
229.255.255.255) refers to the group of hosts
© Janice Regan, 2006-2013
5
Multicasting In a LAN (1)
 Many LANs provide hardware support for
broadcast or multicast
 To send Protocol stack on the host must
map the IP multicast address onto the
appropriate (MAC) multicast or broadcast
addresses.
 To receive the protocol’s network layer must
keep track of processes belonging to each
multicast group (allowing processes to join or
leave the group)
© Janice Regan, 2006-2013
6
Multicasting In a LAN (2)
 If the LAN does not provide hardware support,
(LAN is a non broadcast multi access or NBMA
network)
 map the multicast addresses to local link layer
unicast addresses at the multicast router.
 The multicast router can then send the appropriate
unicast messages to group members
© Janice Regan, 2006-2013
7
Address Translation (1)
 Within an Ethernet the interface to each
host is assigned an Ethernet address
(when manufactured for IPv4)
 The Ethernet address belongs to the
interface, not the host, if the interface is
replaced the Ethernet address will change
 48 bit Ethernet addresses can indicate one
interface, a network broadcast address or a
multicast address.
© Janice Regan, 2006-2013
8
Address Translation (2)
 Within an Ethernet each interface to a
host is assigned an ethernet address
 The interface to a host will extract from the
network packets with





The Ethernet address of the interface itself
The Ethernet network broadcast address
The Ethernet local broadcast address
The Ethernet all hosts multicast group
Any Ethernet multicast addresses of groups the
host is a member of
© Janice Regan, 2006-2013
9
Address Translation (3)
 A multicast router attached to the ethernet will translate
IP addresses to the ethernet multicast or broadcast
addresses, recognizable by the interfaces
 To translate: the lowest 23 bits of the IP multicast
address is placed in the special ethernet address
01.00.5e.00.00.00 (Not a unique mapping as IP has
28 significant bits)
 The non unique mapping means that a multicast host
must check the IP address on a received multicast
packet to assure it is actually a recipient of the packet
(not one of the other 31 of 32 hosts with the same
ethernet multicast address.)
© Janice Regan, 2006-2013
10
Address Translation (4)
225
125
22
5
1 1 1 0 0 0 0 1 0 1 1 1 1 1 0 1 0 0 0 1 0 1 1 0 0 0 0 0 0 1 0 1
0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0 1 1 1 1 0 0 1 1 1 1 1 0 1 0 0 0 1 0 1 1 0 0 0 0 0 0 1 0 1
01
00
5E
The first four bits of the IP address are fixed (they indicate a multicast address)
The next 5 bits (dark blue) are not used in the Ethernet address
Therefore there are 25 = 32 IP addresses with the same Ethernet broadcast address
© Janice Regan, 2006-2013
11
Multicasting Requirements(1)
 Addressing Scheme: locally autonomous assignment
of addresses with global applicability

IPv4 - Class D - start 1110
Address range 224.0.0.0 – 239.255.255.255
 IPv6 - 8 bit prefix, all 1, 4 bit flags field (permanently assigned
or dynamic using IGMP), 4 bit scope field (single network to
global), 112 bit group identifier
 A multicast address can only be a destination address, not a
source address.
 A multicast datagram cannot generate an ICMPv4 message
© Janice Regan, 2006-2013
12
Special multicast addresses
 Just as some unicast IP addresses are reserved for
special purposed, some multicast addresses are
used for special multicast groups
 A list of examples are given in your text (figure 16.2).
 Addresses 224.0.0.0 through 224.0.0.255 are
reserved for special groups and 239.252.0.0 through
239.255.255.255 are restricted to use on a single
site
 You will see and use examples of some special
multicast addresses in your laboratory experiments
© Janice Regan, 2006-2013
13
Special multicast addresses
 224.0.0.0
 224.0.0.1
 224.0.0.2
 224.0.0.4
 224.0.0.5
 224.0.0.8
 224.0.0.13
© Janice Regan, 2006-2013
Reserved network base address
All systems on this subnet (all hosts)
All routers on this subnet (all routers)
All DVMRP Routers
All OSPF Routers
All OSPF Designated Routers
All PIMv2 Routers
14
Multicasting Requirements (2)
 Effective notification and delivery
 Hosts need a mechanism to notify routers about which
groups are of interests to them (IGMP), that is a
mechanism to join and leave multicast groups
 Routers need a mechanism to deliver the multicast
packets to the hosts attached to them
 This mechanism is determined by the type of
network
 Broadcast network
 Non broadcast multiple access network (NBMA)
© Janice Regan, 2006-2013
15
Multicasting Requirements (3)
 Effective notification and delivery
 Routers need a mechanism to deliver the multicast
packets to the hosts attached to them


In a broadcast network the router must translate
between IP multicast address and network multicast
address and multicast packet to group members
In an NBMA network the router must deliver
translate between the multicast address and a list of
unicast IP address in the group then unicast the
packet to all hosts on that list
© Janice Regan, 2006-2013
16
Multicasting Requirements(4)
 An Efficient, Dynamic Forwarding Facility
 Router must translate between IP multicast
addresses and list of networks containing group
members
 Routers must exchange information
 Which networks include members of given group
at a given time
 Sufficient path cost information to work out
shortest path to each network
 Routers must determine ‘shortest’ routing paths
based on source and destination addresses
© Janice Regan, 2006-2013
17
Constraints for efficient
multicast routing:
 Every member host of a multicast group
should receive one copy of the packet
 No host not a member of the multicast
group should receive the packet
 Each router should receive the packet only
once
© Janice Regan, 2006-2013
18
Delivery to multicast group members
 Multiple Unicast
 Send a copy of the packet to each member
of the multicast group
 Not efficient, creates a larger load than
necessary
 Is used only by multicast routers to send
information to members of a multicast group
on an NBMA network
© Janice Regan, 2006-2013
19
Multicast
 Determine least cost path to each network
that has host in group subject to these
constraints
 Gives spanning tree configuration containing
networks with group members
 Transmit one packet along the resulting
spanning tree
 Routers replicate packets at branch points
of the spanning tree
© Janice Regan, 2006-2013
20
Multicast Example
© Janice
Regan,
2006-2013
Stallings
2003:
21
Spanning Tree
 from Router C to Multicast Group
 Must determine multicast routing paths on the
basis of both source and destination addresses
Stallings
2003:
© Janice
Regan,
2006-2013
22
Multicast vs Multiple Unicast
© Janice Regan, 2006-2013
Stallings 2003:
23