Multicasting A message can be unicast, multicast, or
broadcast.
Slide 2
Unicasting In unicasting, the router forwards the received
packet through only one of its interfaces.
Slide 3
Multicasting
Slide 4
In multicasting, the router may forward the received packet
through several of its interfaces. In multicasting communications
there is one source and a group of destinations In broadcasting
there is one source but all of other hosts are the
destinations
Slide 5
Multicasting and multiple unicasting Multicasting starts with
one single packet from the source that is duplicated by the router
The destination address in each packet is the same for all
duplicates In multiple unicasting several packets starts from the
source. Destination address will be different in each packet There
may be multiple copies traveling between two routers---E.g. Email
There will be a delay between packets in MU
Slide 6
Multicasting versus multiple unicasting
Slide 7
Multicast Applications Multicasting has many applications today
such as access to distributed databases information dissemination
teleconferencing distance learning
Slide 8
Multicast Routing In multicast routing, each involved router
needs to construct a shortest path tree for each group When a
router receives a multicast packet it forwards to different
networks Two types Source based tree Group shared tree
Slide 9
Source Based Tree In the source-based tree approach, each
router needs to have one shortest path tree for each group. If the
number of groups is m, each router needs to have m shortest path
trees, one for each group
Slide 10
Source-based tree approach
Slide 11
Group Shared Tree In the group-shared tree approach, only the
core router, which has a shortest path tree for each group, is
involved in multicasting. Instead of each router having m shortest
path tree, only one designated router called the centre core or
rendezvous router, takes the responsibility of distributing
multicast traffic
Slide 12
Group-shared tree approach
Slide 13
Taxonomy of common multicast protocols
Slide 14
Mulitcast link state routing Multicast link state routing uses
the source- based tree approach. Information about a group comes
from IGMP
Slide 15
Multicast Open Shortest Path First (MOSPF) Multicast Open
Shortest Path First protocol is an extension of OSPF protocol that
uses multicast link state routing to create source based tree.
Slide 16
Multicast distance vector routing Multicast distance vector
routing uses source based tree But router never makes the routing
table When a router receives a multicast packet it forwards the
packet as though it is consulting a routing table.
Slide 17
Flooding A router receives a packet and without even looking at
the destination group address, send it out from every interface
except the one from which it was received.
Slide 18
Reverse path forwarding(RPF) In RPF a router forwards only the
copy that has traveled the shortest path from the source to the
router. No loops But duplicate copies may receive
Slide 19
RPF
Slide 20
Figure 15.9 Problem with RPF
Slide 21
Reverse Path Broadcasting(RPB)
Slide 22
Figure 15.10 RPF versus RPB
Slide 23
Reverse path multicating(RPM) RPM adds pruning and grafting to
RPB to create a multicast shortest path tree that supports dynamic
membership changes
Slide 24
RPF, RPB, and RPM
Slide 25
Distance Vector Multicast Routing Protocol (DVMRP) Is an
implementation of multicast distance vector routing. It is a source
based routing protocol
Slide 26
CBT The Core-Based Tree (CBT) protocol is a group-shared
protocol that uses a core as the root of the tree. The autonomous
system is divided into regions and a core (center router or
rendezvous router) is chosen for each region.
Slide 27
Every router is informed of the unicast address of the selected
rendezvous router Each router then sends a unicast join message
Intermediate router extracts information such as unicast address of
sender and interfaces through which it has passed When all message
received a tree is formed at rendezvous router
Slide 28
Group-shared tree with rendezvous router
Slide 29
Sending a multicast packet to the rendezvous router
Slide 30
In CBT, the source sends the multicast packet (encapsulated in
a unicast packet) to the core router. The core router decapsulates
the packet and forwards it to all interested interfaces
Slide 31
If router wants to leave the group it sends a leave message to
upstream router. Difference between DVMRP 1) tree is first made and
then pruned but in CBT initial no tree, joining gradually makes the
tree 2) made from the root up but CBT formed from the leaves
down
Slide 32
32 PIM Protocol Independent Multicast (PIM) is the name given
to two independent multicast routing protocols: Protocol
Independent Multicast, Dense Mode (PIM-DM) and Protocol Independent
Multicast, Sparse Mode (PIM-SM).
Slide 33
33 PIM-DM is used in a dense multicast environment, such as a
LAN.
Slide 34
34 PIM-DM uses RPF and pruning/grafting strategies to handle
multicasting. Like DVMRP,However, it is independent from the
underlying unicast protocol.
Slide 35
35 PIM-SM is used in a sparse multicast environment such as a
WAN.
Slide 36
36 PIM-SM is similar to CBT but uses a simpler procedure. Does
not require acknowledgement Creates backup set of rendezvous point
for each region to cover RP failures Can switch from group shared
tree to source based tree
Slide 37
Host Configuration: BOOTP and DHCP
Slide 38
BOOTP The Bootstrap Protocol (BOOTP) is a client/server
protocol that configures a diskless computer or a computer that is
booted for the first time. BOOTP provides the IP address, subnet
mask, the address of a default router, and the address of a name
server. Configuration file
Slide 39
RARP provides only IP address Both client and server should be
on same network
Slide 40
Operations BOOTP server issues a passive open command on UDP
port number 67 and waits for client A BOOTP client issues an active
open command on port number 68 This message is encapsulated in UDP
datagram and in turn encapsulated in IP datagram IP addresses of
client and server will be all zeros and all ones Server
responds
Slide 41
Client and server on the same network
Slide 42
Client and server on two different networks
Slide 43
Use of UDP ports
Slide 44
Using TFTP In the reply message server defines the path name of
a file in which the client can find complete booting information.
Client then uses TFTP to obtain the rest of information
Slide 45
Error Control BOOTP requires UDP uses the checksum BOOTP client
uses timers and a retransmission policy if it does not receive the
BOOTP reply to a request. Timers will be set randomly
Slide 46
BOOTP packet format
Slide 47
Operation Code: 8 bit: 1 request 2 reply Hardware type: type of
physical network for Ethernet value is 1 Hardware Length: 8 bit:
length of physical address Hop count: 8bit Specifies max no of hops
a packet can travel Transaction ID: 4 byte: integer Number of
seconds: 16 bit: elapsed since the client started to boot Client IP
address : 4 byte Your IP address : 4 byte
Slide 48
Server IP address : 4 byte Gateway IP address: 4 byte: IP
address of router Client hardware address: Physical address of
client Server name: optional 64 byte : contains domain name of the
server Bootfile name: optional 128 byte: full path name of the
bootfile Options: 64 byte: only in reply it is used server uses a
number called magic cookie in the format of IP address with the
value: 99.130.83.99
Slide 49
Option format
Slide 50
Options for BOOTP
Slide 51
DHCP In BOOTP binding is predetermined The Dynamic Host
Configuration Protocol (DHCP) provides static and dynamic address
allocation that can be manual or automatic
Slide 52
Static Address allocation Backward compatible with BOOTP A DHCP
server has a database that statically binds physical address to IP
address
Slide 53
Dynamic Address Allocation Use a second database- pool of IP
addresses When a DHCP client requests First check the static
database If not, the DHCP server selects a temporary IP address
from the pool of available(unused) and assigns an IP address for a
negotiable period of time.
Slide 54
Manual and automatic configuration Mapping the IP address to
physical address configuration In BOOTP it is manual In DHCP it has
both manual and automatic Static addresses are created manually
Dynamic addresses are created automatically
Slide 55
Packet Format
Slide 56
DHCP packet
Slide 57
Flag 1 bit flag to let the client specify a forced broadcast
reply from the server
Slide 58
Options Tag 53
Slide 59
Options Other option include 51 :Lease time 58 : Renewal (T1)
time value 59 : Rebinding (T2) time value
Slide 60
Transition States DHCP client transitions from one state to
another depending on the message it receives or sends
Slide 61
DHCP transition diagram
Slide 62
Initializing state When the DHCP client first starts, it is in
the initializing state. Client broadcast the DHCPDISCOVER message
Using port 67
Slide 63
Selecting State After sending DHCPDISCOVER message client goes
to selecting state Servers respond with DHCPOFFER Offers IP
address, Lease time Default lease time is 1hour Client select the
offer of one server and send DHCPREQUEST message Client goes to
requesting state
Slide 64
Requesting State The client remains in the requesting state
until it receives a DHCPACK message from the server which creates a
binding between the client physical address and its IP address.
After the receipt of DHCPACK client goes to bound state
Slide 65
Bound State Client uses the IP address until the lease expires
When 50% of the lease period is reached, client sends another
DHCPREQUEST to ask for renewal. Then goes to renewal state
Slide 66
Renewal state Client remains in the renewal state until one of
two events happens 1) It can receive a DHCPACK, which renews the
lease agreement Client reset the timer goes back to bound
state
Slide 67
2) No DHCPACK is received and 87.5 % of the lease time expires,
the client goes to rebinding state
Slide 68
Rebinding state The client remains in rebinding state until of
three events happens 1) Client receives a DHCPNACK 2) The lease
time expires 3) DHCPACK In the first two it goes to initializing
state and try to get another IP address In the third it goes to
bound state
