Download Broadcast and Multicast Using Sockets

Broadcast and Multicast
Unicast
Host 1
Host 2
Broadcast
Packet received by every host on network (including the sender!)
Multicast
Packet received by a selected subset of hosts in the network
Root
Leaf
Leaf
Broadcast
• Advantages
– Reducing Network Traffic
• Network Time Protocol (NTP), Route Broadcasts
– Resource Discovery
• ARP, BOOTP
Broadcast…
• Disadvantage
– Everybody receives a packet, whether they
want it or not.
• Receving a packet Interrupting your work and
processing the packet.
Types of broadcast addresses
• IP Address can be broken down as
{netid, subnetid, hostid}
E.g. 130.245.224.19
130.245  Netid
224  subnet id
19  host id
Types of broadcast addresses…
• Subnet-directed broadcast
{netid, subnetid, *}
E.g. 130.245.224.255
• Broadcasts to local subnet.
• Routers do not forward these types of
broadcast.
Types of broadcast addresses…
• All-Subnet broadcast
{netid, *, *}
E.g. 130.245.255.255
• Broadcasts to all subnets under netid
• Almost never used. May not be allowed for
administrative reasons.
Types of broadcast addresses…
• Network directed broadcast
{netid, *}
• For networks without sub-netting
• Doesn’t exist anymore
Types of broadcast addresses…
• Limited broadcast address
{*, *, *}
E.g. 255.255.255.255
• Older form of Subnet-directed broadcast
• Broadcasts to local subnet
• Never forwarded across routers.
How broadcast works
Sender
Dest IP = 130.245.224.255
Dest Port = 9999
Receiver
Port 9999
UDP
UDP
IPv4
IPv4
IPv4
Data Link
Data Link
Data Link
UDP
X
Dest Ethernet addr
ff:ff:ff:ff:ff:ff
Example
Echo from Multiple Servers
int sockfd, on=1, len;
char recvline[MAXLILNE];
struct sockaddr_in reply_addr, bcastaddr;
sockfd = Socket(…);
/* Enable broadcast on socket */
Setsockopt(sockfd, SOL_SOCKET,SO_BROADCAST, &on,
sizeof(on));
/* Set a receive timeout on socket */
tv.tv_sec = 5;
tv.tv_usec = 0;
Setsockopt( sockfd, SOL_SOCKET, SO_RCVTIMEO, (void *)&tv,
sizeof(tv));
Initialize bcastaddr with IP = 130.245.224.255 and
Port = 9999
/* Broadcast a Hello */
Sendto(sockfd, “Hello”, strlen(“Hello”), 0, (struct sockaddr
*)&bcastaddr, sizeof(bcastaddr));
/* Receive Echos from servers*/
for(;;) {
len = sizeof(reply_addr);
n = recvfrom (sockfd, recvline, MAXLINE, 0, &reply_addr, &len);
if( n < 0) {
if (errno == EAGAIN) {
printf(“Waited for 5 seconds - exiting\n”);
} else {
perror(“ERROR”);
}
exit(0);
}
recvline[n] = 0;
printf(“%s\n”, recvline);
}
Multicast
Multicast addresses
• Class D address :
– 224.0.0.0 to 239.255.255.255
• Low order 28 bits identify a multicast group id.
• Link Local addresses :
– 224.0.0.0 to 224.0.0.255
– Reserved for network maintenance messages
– Never forwarded by routers
• All-hosts group - 224.0.0.1
• All-routers group - 224.0.0.2
Multicast to Ethernet mapping
28-bit group ID
e
01
00
5e
Low order 23 bits
32 IP multicast groups map to one Ethernet level multicast group
How multicast works
Sender
Join
224.0.1.1
Dest IP = 224.0.1.1
Dest Port = 9999
Receiver
Port 9999
UDP
UDP
UDP
IPv4
IPv4
IPv4
Data Link
Data Link
Data Link
Receive
01:00:5e:00:01:01
Dest Ethernet addr
01:00:5e:00:01:01
Managing multicast membership
• Five Socket options
– IP_ADD_MEMBERSHIP
• Join a multicast group
– IP_DROP_MEMBERSHIP
• Leave a multicast group
– IP_MULTICAST_IF
• Specify a default interface for outgoing multicast
– IP_MULTICAST_TTL
• Specify TTL for outgoing multicast
– IP_MULTICAST_LOOP
• Enable or disable loopback of outgoing multicast
WAN Multicast
Sender
R3
S1
S4
R1
S2
R2
S – subnet
R - Router
- Receiver
S3