Broadcast and Multicast

1. Broadcast and Multicast

2. Unicast Host 1 Host 2

3. Broadcast Packet received by every host on network (including the sender!)

4. Multicast Packet received by a selected subset of hosts in the network Root Leaf Leaf

5. Broadcast • Advantages • Reducing Network Traffic • Network Time Protocol (NTP), Route Broadcasts • Resource Discovery • ARP, BOOTP

6. Broadcast… • Disadvantage • Everybody receives a packet, whether they want it or not. • Receving a packet Interrupting your work and processing the packet.

7. 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

8. 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.

9. 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.

10. Types of broadcast addresses… • Network directed broadcast {netid, *} • For networks without sub-netting • Doesn’t exist anymore

11. 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.

12. How broadcast works Dest IP = 130.245.224.255 Receiver Sender Dest Port = 9999 Port 9999 UDP UDP UDP X IPv4 IPv4 IPv4 Data Link Data Link Data Link Dest Ethernet addr ff:ff:ff:ff:ff:ff

13. Example Echo from Multiple Servers

14. 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

15. /* 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); }

16. Multicast

17. 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

18. 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

19. How multicast works Join 224.0.1.1 Dest IP = 224.0.1.1 Receiver Sender Dest Port = 9999 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

20. 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

21. WAN Multicast Sender R3 S1 S4 R1 S2 R2 S – subnet R - Router S3 - Receiver