Chaptere19 multicasting

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Chaptere19multicasting
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contents

• multicast address
• multicasting versus broadcasting on a LAN
• multicasting on a WAN
• multicast socket option
• mcast_join and related function
• dg_cli function using multicasting
• receiving MBone session announcements
• sending and receiving
• SNTP

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• Unicast
• a single interface
• broadcast
• multiple interfaces
• LAN
• multicast
• a set of interfaces
• LAN or WAN
• Mbone
• five socket opetions

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multicast address

• IPv4 class D address
• 224.0.0.0 239.255.255.255
• (224.0.0.1 all hosts group), (224.0.0.2
  all-routers group)

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multicast address(2)

• IPv6 multicast address
• special IPv6 multicast address
• ff021 gt all-nodes group(all multicast-capable
  hosts on subnet must join this group on all
  multicast-capable interfaces)
• ff022 gt all-routers group(all
  multicast-capable routers on subnet must join
  this group on all multicast-capable interfaces)

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Scope of multicast addresses

• IPv6 multicast address have an explicit 4-bit
  scope field that specifies how far the multicast
  packet will travel.
• Node-local (1)
• link-local (2)
• site-local (5)
• organization-local (8)
• global (14)
• remaining values are unassigned or reserved

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multicasting versus broadcasting on a LAN

• One host sends a multicast packet and any
  interested host receives the packet.
• Benefit
• reducing the load on all the hosts not interested
  in the multicast packets

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multicasting on a WAN
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A host sends the audio packets and the multicast
receivers are waiting to receive
MRP Multicast Routing Protocol
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multicast socket option

• The API support for multicasting requires only
  five new socket options.
• Figure 19.7

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multicast socket option(2)

• IP_ADD_MEMBERSHIP, IPV6_ADD_MEMBERSHIP
• join a multicast group on s specified local
  interface.

Struct ip_mreq struct in_addr imr_multiaddr stru
ct in_addr imr_interface
Struct ipv6_mreq struct in6_addr
ipv6mr_multiaddr struct int ipv6mr_interface
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multicast socket option(3)

• IP_DROP_MEMBERSHIP, IPV6_DROP_MEMBERSHIP
• leave a multicast group on a specified local
  interface.
• If the local interface is not specified, the
  first matching multicasting group membership is
  dropped.

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multicast socket option(4)

• IP_MULTICAST_IF, IPV6_MULTICAST_IF
• specify the interface for outgoing multicast
  datagrams sent on this socket.
• This interface is specified as either an in_addr
  structure for IPv4 or an interface index for IPv6.

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multicast socket option(5)

• IP_MULTICAST_TTL, IPV6_MULTICAST_TTL
• set the IPv4 TTL or the IPv6 hop limit for
  outgoing multicast datagrams.
• If this is not specified , both default to 1,
  which restricts the datagram to the local subnet.

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multicast socket option(6)

• IP_MULTICAST_LOOP, IPV6_MULTICAST_LOOP
• enable or disable local loopback of multicast
  datagrams.
• Default loopback is enabled.
• This is similar to broadcasting.

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mcast_join and related function

• include unp.h
• int mcast_join(int sockfd, const struct sockaddr
  addr, socklen_t salen, const char ifname, u_int
  ifindex)
• int mcast_leave(int sockfd, const struct sockaddr
  addr, socklen_t salen)
• int mcast_set_if(int sockfd, const char ifname,
  u_int ifindex)
• int mcast_set_loop(int sockfd, int flag)
• int mcast_set_ttl(int sockfd, int ttl)
• All above return 0 if ok, -1 on
  error
• int mcast_get_if(int sockfd)
• return nonnegative interface index if OK,
  -1 error
• int mcast_get_loop(int sockfd)
• return current loopback flag if OK, -1
  error
• int mcast_get_ttl(int sockfd)
• return current TTL or hop limit if OK, -1
  error

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• include "unp.h"
• include ltnet/if.hgt
• int mcast_join(int sockfd, const SA sa,
  socklen_t salen, const char ifname, u_int
  ifindex)
• switch (sa-gtsa_family)
• case AF_INET
• struct ip_mreq mreq
• struct ifreq ifreq
• memcpy(mreq.imr_multiaddr, ((struct
  sockaddr_in ) sa)-gtsin_addr,
• sizeof(struct in_addr))
• if (ifindex gt 0)
• if (if_indextoname(ifindex, ifreq.ifr_name)
  NULL)
• errno ENXIO / i/f index not found /
• return(-1)
• goto doioctl
• else if (ifname ! NULL)

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• ifdef IPV6
• case AF_INET6
• struct ipv6_mreq mreq6
• memcpy(mreq6.ipv6mr_multiaddr, ((struct
  sockaddr_in6 ) sa)-gtsin6_addr,
• sizeof(struct in6_addr))
• if (ifindex gt 0)
• mreq6.ipv6mr_interface ifindex
• else if (ifname ! NULL)
• if ( (mreq6.ipv6mr_interface
  if_nametoindex(ifname)) 0)
• errno ENXIO / i/f name not found /
• return(-1)
• else
• mreq6.ipv6mr_interface 0
• return(setsockopt(sockfd, IPPROTO_IPV6,
  IPV6_ADD_MEMBERSHIP,
• mreq6, sizeof(mreq6)))

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• include "unp.h"
• int mcast_set_loop(int sockfd, int onoff)
• switch (sockfd_to_family(sockfd))
• case AF_INET
• u_char flag
• flag onoff
• return(setsockopt(sockfd, IPPROTO_IP,
  IP_MULTICAST_LOOP,
• flag, sizeof(flag)))
• ifdef IPV6
• case AF_INET6
• u_int flag
• flag onoff
• return(setsockopt(sockfd, IPPROTO_IPV6,
  IPV6_MULTICAST_LOOP, flag, sizeof(flag)))
• endif
• default

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dg_cli function using multicasting
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Receiving MBone session announcements

• To receive a multimedia conference on the MBone
  a site needs to know only the multicast address
  of the conference and the UDP ports for the
  conferences data streams.(audio, video)
• SAP(Session Announce Protocol)
• describe the way
• SDP(Session Description Protocol)
• the contents of these announcements

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• A site wishing to announce a session on the Mbone
• periodically sends a multicast packet containing
  a description of the session to a well-known
  multicast group and UDP port
• Sites on Mbone
• run sdr program
• receives these announcements
• provides an interactive user interface that
  displays the information
• lets user send announcements
• A sample program
• only receives these session announcements to show
  an example of a simple multicast receiving
  program

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The program receiving the periodic SAP/SDP
announcements

• include "unp.h"
• define SAP_NAME "sap.mcast.net" / default group
  name and port /
• define SAP_PORT "9875"
• void loop(int, socklen_t)
• int main(int argc, char argv)
• int sockfd
• const int on 1
• socklen_t salen
• struct sockaddr sa
• if (argc 1)
• sockfd Udp_client(SAP_NAME, SAP_PORT, (void
  ) sa, salen)
• else if (argc 4)
• sockfd Udp_client(argv1, argv2, (void )
  sa, salen)
• else err_quit("usage mysdr ltmcast-addrgt ltportgt
  ltinterface-namegt")
• Setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR,
  on, sizeof(on))
• Bind(sockfd, sa, salen)

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• include "unp.h"
• void loop(int sockfd, socklen_t salen)
• char bufMAXLINE1
• socklen_t len
• ssize_t n
• struct sockaddr sa
• struct sap_packet
• uint32_t sap_header
• uint32_t sap_src
• char sap_data1
• sapptr
• sa Malloc(salen)
• for ( )
• len salen
• n Recvfrom(sockfd, buf, MAXLINE, 0, sa,
  len)
• bufn 0 / null terminate /
• sapptr (struct sap_packet ) buf
• if ( (n - 2 sizeof(uint32_t)) lt 0)

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sending and receiving

• Sends and receives multicast datagrams
• First part
• sends a multicast datagram to a specific group
  every 5 seconds and the datagram contains the
  senders hostname and process ID
• Second part
• an infinite loop that joins the multicast group
  to which the first part is sending and prints
  every received datagrams

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• include "unp.h"
• void recv_all(int, socklen_t)
• void send_all(int, SA , socklen_t)
• int main(int argc, char argv)
• int sendfd, recvfd
• const int on 1
• socklen_t salen
• struct sockaddr sasend, sarecv
• if (argc ! 3) err_quit("usage sendrecv
  ltIP-multicast-addressgt ltportgt")
• sendfd Udp_client(argv1, argv2, (void )
  sasend, salen)
• recvfd Socket(sasend-gtsa_family, SOCK_DGRAM,
  0)
• Setsockopt(recvfd, SOL_SOCKET, SO_REUSEADDR,
  on, sizeof(on))
• sarecv Malloc(salen)
• memcpy(sarecv, sasend, salen)
• Bind(recvfd, sarecv, salen)

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• include "unp.h"
• include ltsys/utsname.hgt
• define SENDRATE 5 / send one datagram every 5
  seconds /
• void
• send_all(int sendfd, SA sadest, socklen_t salen)
• static char lineMAXLINE / hostname and
  process ID /
• struct utsname myname
• if (uname(myname) lt 0)
• err_sys("uname error")
• snprintf(line, sizeof(line), "s, d\n",
  myname.nodename, getpid())
• for ( )
• Sendto(sendfd, line, strlen(line), 0, sadest,
  salen)
• sleep(SENDRATE)

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• include "unp.h"
• void
• recv_all(int recvfd, socklen_t salen)
• int n
• char lineMAXLINE1
• socklen_t len
• struct sockaddr safrom
• safrom Malloc(salen)
• for ( )
• len salen
• n Recvfrom(recvfd, line, MAXLINE, 0, safrom,
  len)
• linen 0 / null terminate /
• printf("from s s", Sock_ntop(safrom, len),
  line)

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SNTP

• NTP gt so sophisticated protocol
• SNTP gt simplified version of NTP
• hosts do not need the complexity of a complete
  NTP implementation.
• A client listening for NTP broadcast or
  multicasts on all attached networks and then
  prints the time difference between the NTP packet
  and the hosts current time-of-day

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• define JAN_1970 2208988800UL / 1970 - 1900 in
  seconds /
• struct l_fixedpt / 64-bit fixed-point /
• uint32_t int_part
• uint32_t fraction
• struct s_fixedpt / 32-bit fixed-point /
• u_short int_part
• u_short fraction
• struct ntpdata / NTP header /
• u_char status
• u_char stratum
• u_char ppoll
• int precision8
• struct s_fixedpt distance
• struct s_fixedpt dispersion
• uint32_t refid
• struct l_fixedpt reftime
• struct l_fixedpt org
• struct l_fixedpt rec
• struct l_fixedpt xmt

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• include "sntp.h"
• int main(int argc, char argv)
• int sockfd
• char bufMAXLINE
• ssize_t n
• socklen_t salen, len
• struct ifi_info ifi
• struct sockaddr mcastsa, wild, from
• struct timeval now
• if (argc ! 2) err_quit("usage ssntp
  ltIPaddressgt")
• sockfd Udp_client(argv1, "ntp", (void )
  mcastsa, salen)
• wild Malloc(salen)
• memcpy(wild, mcastsa, salen) / copy family and
  port /
• sock_set_wild(wild, salen)

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Figure 19.18 ( 2/2 )

• ifdef MCAST
• / 4obtain interface list and process each one
  /
• for (ifi Get_ifi_info(mcastsa-gtsa_family, 1)
  ifi ! NULL
• ifi ifi-gtifi_next)
• if (ifi-gtifi_flags IFF_MULTICAST)
• Mcast_join(sockfd, mcastsa, salen,
  ifi-gtifi_name, 0)
• printf("joined s on s\n",
• Sock_ntop(mcastsa, salen), ifi-gtifi_name)
• endif
• from Malloc(salen)
• for ( )
• len salen
• n Recvfrom(sockfd, buf, sizeof(buf), 0, from,
  len)
• Gettimeofday(now, NULL)
• sntp_proc(buf, n, now)

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• include "sntp.h
• void sntp_proc(char buf, ssize_t n, struct
  timeval nowptr)
• int version, mode
• uint32_t nsec, useci
• double usecf
• struct timeval curr, diff
• struct ntpdata ntp
• if (n lt sizeof(struct ntpdata))
• printf("\npacket too small d bytes\n", n)
• return
• ntp (struct ntpdata ) buf
• version (ntp-gtstatus VERSION_MASK) gtgt 3
• mode ntp-gtstatus MODE_MASK
• printf("\nvd, mode d, strat d, ", version,
  mode, ntp-gtstratum)
• if (mode MODE_CLIENT)

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• nsec ntohl(ntp-gtxmt.int_part) - JAN_1970
• useci htonl(ntp-gtxmt.fraction) / 32-bit
  integer fraction /
• usecf useci / integer fraction -gt double
  /
• usecf / 4294967296.0 / divide by 232 -gt
  0, 1.0) /
• useci usecf 1000000.0 / fraction -gt parts
  per million /
• curr nowptr / make a copy as we might
  modify it below /
• if ( (diff.tv_usec curr.tv_usec - useci) lt 0)
  
• diff.tv_usec 1000000
• curr.tv_sec--
• diff.tv_sec curr.tv_sec - nsec
• useci (diff.tv_sec 1000000)
  diff.tv_usec / diff in microsec /
• printf("clock difference d usec\n", useci)

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SNTP(2)
One socket per unicast address One socket per
broadcast address One socket per interface on
which the multicast group is joined
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