Broadcast and Multicast Unicast Host 1 Host 2

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

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 • 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 • 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 IPv 4 Data Link UDP X Dest Ethernet addr 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 - exitingn”); } else { perror(“ERROR”); } exit(0); } recvline[n] = 0; printf(“%sn”, recvline); }

Multicast

Multicast addresses • Class D address : – 224. 0. 0. 0 to 239. 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 5 e 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 IPv 4 Data Link Receive 01: 00: 5 e: 00: 01 Dest Ethernet addr 01: 00: 5 e: 00: 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 R 3 S 1 S 4 R 1 S 2 R 2 S – subnet R - Router - Receiver S 3