1. Broadcasting & Multicasting with UDP sockets Chap 20, 21

2. Broadcasting

3. Introduction  Use of broadcasting  to know server address on the local subnet: resource discovery  to minimize network traffic on a LAN  Internet applications  ARP(Address Resolution Protocol)  BOOTP(Bootstrap Protocol)  NTP(Network Time Protocol)  Routing daemons: broadcast routing table

4. Broadcast Addresses  Subnet-directed: [subnetid, -1]  most commonly used today  e.g.) ping 203.253.70.255  Limited broadcast: 255.255.255.255  All hosts on the same LAN  must not forwarded by a router  Some systems do not understand a subnet- directed broadcast address and only interpret 255.255.255.255 as a broadcast  TFTP and BOOTP use this limited broadcast address to know IP address of its diskless workstation on bootstrapping procedure

5. Unicast versus Broadcast

6. dg_cli Function that broadcasts  Before broadcasting, set SO_BROADCAST socket option  문제점  만일 timeout 이 짧다면 ??  SIGALRM signal 이 blocked system call (recvfrom) 이외에서 deliver 되면 loop 을 빠져 나오지 못함  해결방안 1: recvfrom 외에는 ALRM signal 이 뜨지 않게 만들자. 즉, signal 을 block 시킴. (Fig. 20.6, bcast/dgclibcast3.c)  그래도 race condition 이 발생할 수 있음  Race Condition:  shared data 를 여러 process 들이 동시에 access 할 때 time- dependent error 발생  Case 1: shared data (global variable) among threads  Case 2: dealing with signals  signal handler 도 일종의 thread 로 봐야 bcast/dgclibcast1.c

7. Correct Solutions for Avoiding Race Condition bcast/dgclibcast5.c

8. Multicasting

9. Multicast Address  Multicast(Group) address: IPv4 Class D Addresses  IPv4  224.0.0.0 - 239.255.255.255(first 4bit: 1110)  Special IPv4 multicast addresses   224.0.0.1 all-hosts group (on a subnet, i.e. link-local)   224.0.0.2 all-routers group (on a subnet, i.e. link-local)  IPv6 Multicast Addresses  ff01::1, ff02::1 all-nodes group (interface-local, link-local)  ff01::2, ff02::2, ff05::2 all-routers group(…, site-local) Scope of multicast addresses

10. Multicasting in broadcast-capable LANs  Just Map IP address to Ethernet Address  Then, LAN will delivers.

11. Multicast Protocols  IP Multicasting  특정 Group 에 Join 해야 수신할 수 있음  Sender 는 단지 Group 주소 (Class D address) 로 하나의 packet 을 보냄  Network( 즉, 라우터 ) 가 Group 에 속한 member 에게 전달할 책임 있음 (copy 는 router 책임 )  Join/leave a group: IGMP( Internet Group Membership Protocol)  Application 은 setsockopt() 으로 호출  Multicast Routing Protocol  Find multicast tree  E.g) PIM, M-OSPF  LAN 내부에서의 multicast 에는 필요 없음  Multicast Types  Any-source Multicast (ASM)  (*, G)  Source-Specific Multicast (SSM)  Similar to TV channels  Member may join a channel (S, G)

12. Multicast versus Broadcast

13. Multicast Session  A multicast session  Defined by (IP multicast addr, UDP port)  Always use different ports  Sometimes use different groups  Audio/video conference may require two multicast sessions  A session for audio  A session for video

14. Senders: Sending Multicast Datagrams  Specify interface, TTL, and enable/disable loop back  Default,  Interface for outgoing datagram will be chosen by kernel  TTL or hop limit == 1  Enable loop back: sender 도 보낸 패킷을 받음  e.g. Disable loop back setsockopt(sockfd, IPPROTO_IP, IP_MULTICAST_LOOP, &flag, sizeof(flag));  Send datagrams to all the members of group G (ASM 인 경우 )  Sender app: set destination socket addr to (G, port); sendto();  Sender 의 send socket 에 꼭 bind 할 필요는 없음. Why?  Internet 은 Multicast routing protocol 에 의해 receiver host 들을 담당하는 local router 까지의 Multicast tree 를 구성함  When? Dynamic(PIM-SM, PIM-DM, DVMRP, OSPF) or static (shared tree: e,g CBT)  Multicast tree 를 따라 중간 라우터는 copy 하여 forwarding 하고, 결국, local router 는 다시 receiver 의 host 로 forward 함

15. Receivers: Receiving Multicast Datagrams  Join the multicast group  Ask the kernel for joining the group struct ip_mreq mreq; struct in_addr group_addr; memcpy(&mreq.imr_multiaddr, group_addr, sizeof(group_addr)); setsockopt(sockfd, IPPROTO_IP, IP_ADDMEMBERSHIP, &mreq, sizeof(mreq));  Kernel joins the Group using IGMP  이 group G 로 보내는 IP multicast packet 들이 receiver 의 host computer (i.e IP protocol) 에게도 보내달라고 Internet (router) 에게 요청함  Bind [the group address and] port for the multicast session  Multicast session (G, port) 으로 전달된 packet 을 Kernel 이 Receiver application 의 해당 socket 으로 전달하도록 요청  Receive datagrams: recvfrom()

16. Multicast Socket Options IPv4, ASM IPv4, SSM IPv6, ASM IPv4/v6, ASM IPv4/v6, SSM

17. UNP Library For Supporting Protocol- independent Multicast Application

18. Joining Multicast Group lib/mcast_join.c

19. Sending and Receiving Multicast Packets mcast/main.c mcast/send.c mcast/recv.c