VIII Multicasting Options

7/17/2019 VIII Multicasting Options

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Chaptere19

multicasting



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 Mone session announcements

• sending and receiving

• !N"#



M$L"%CA!"%N&

TCP/IP ProtocolSuite

3



'ifference b() multicasting and multiple unicasting

• Multicasting starts )ith one single packet from the source that is duplicated b* the

routers+ "he destination address in each packet is the same for all duplicates

• %n multiple unicasting, several packets start from the source )ith different

destination address+ -or e.ample, )hen a person sends an e/mail message to a

group of people, this is multiple unicasting+ "he e/mail soft)are creates replicas of

the message, each )ith a different destination address, and sends them one b* one+


4



Applications of Multicasting

• "eleconferencing

• 'istance Learning

• 'issemination of Ne)s

• Access to distributed database


5



Multicast Address• A multicast address is a destination address for a group of hosts

that have 0oined a multicast group+

• A packet that uses a multicast address as a destination can reach

all members of the group unless there are some filtering

restriction b* the receiver+• Multicast Address used in IPV4: %n classful addressing,

multicast addresses occupied the onl* single block in class '+ %n

classless addressing the same block has been used for this

purpose+

• %n other )ords, the block assigned for multicasting is 2+3+3+3(2+

"his means that the block has 45 6 75,28,27 addresses

:2+3+3+3 to 89,++;+


6



'eliver* of Multicast #ackets at 'ata Link La*er

• ecause the %# packet has a multicast %# address, the A<# protocol cannot

find the corresponding MAC :ph*sical; address to for)ard the packet at

the data link la*er+

• What happens ne.t depends on )hether or not the underl*ing data link

la*er supports ph*sical multicast addresses+

• Most LANs support ph*sical multicast addressing+ =thernet is one of them+

• An =thernet ph*sical address :MAC address; is si. octets :25 bits; long+ %fthe first bits in an =thernet address are 33333331 33333333 31311113

3, this identifies a ph*sical multicast address for the "C#(%# protocol+

• "he remaining 8 bits can be used to define a group+

• "o convert an %# multicast address into an =thernet address, the multicast

router e.tracts the least significant 8 bits of a multicast %# address andinserts them into a multicast =thernet ph*sical address


7




8

Figure 10.10 Mapping class D to Ethernet

physical address




9

An Ethernet multicast physical address

is in the range01:00:5E:00:00:00

to

01:00:5E:7F:FF:FF.

Note> Note>




10

Change the multicast IP address 20.!.1!.7 to an Ethernet

multicast physical

Example 2

"olution

#e can do this in t$o steps:a. #e $rite the rightmost 2 %its o& the IP address in he'adecimal. (his

can %e done %y changing the rightmost %ytes to he'adecimal and then

su%tracting ) &rom the le&tmost digit i& it is greater than or e*ual to ). In

our e'ample+ the result is 2,:0E:07.

%. #e add the result o& part a to the starting Ethernet multicast address+

$hich is -01:00:5E:00:00:00. (he result is

31>33>=>>3=>3?




11

Change the multicast IP address 2).212.2!./ to an Ethernet

multicast address.

Example 3

"olution

a. (he rightmost three %ytes in he'adecimal are !:1):0/. #e need to

su%tract ) &rom the le&tmost digit+ resulting in 5!:1):0/..

%. #e add the result o& part a to the Ethernet multicast starting address.

(he result is

01:00:5E:54:18:09



• $nicast @ a single interface

• broadcast

@ multiple interfaces

@ LAN• multicast

@ a set of interfaces

@ LAN or WAN

@ Mbone @ five socket opetions



multicast address• %#v2 class ' address

@ 2+3+3+3 89+++

@ :2+3+3+1> all hosts group;, :2+3+3+> all/routers group;



multicast address:;

• %#v7 multicast address

• special %#v7 multicast address :flags;

@ ff3>>1 6B all/nodes group:all multicast/capable hosts on subnetmust 0oin this group on all multicast/capable interfaces;

@ ff3>> 6B all/routers group:all multicast/capable routers on subnet

must 0oin this group on all multicast/capable interfaces;



!cope of multicast addresses

• %#v7 multicast address have an e.plicit 4-bit scoe !ield

that seci!ies "o# !ar t"e $ulticast ac%et #ill tra&el+

@ Node/local :1; @ link/local :;

@ site/local :;

@ organiation/local :5;

@ global :12;

• remaining values are unassigned or reserved



• DErganiation must set its boundar* routers not to for)ard

multicast packets outside net)ork



multicasting versus broadcasting on a

LAN• Ene host sends a multicast packet and an* interested host

receives the packet+

• enefit

@ reducing the load on all the hosts not interested in the multicast

packets





multicasting on a WAN



A host sends the audio packets and the multicast receivers are

)aiting to receive

M<#> Multicast <outing #rotocol





multicast socket option

• "he A#% support for multicasting reFuires onl* five ne)

socket options+

• -igure 19+?



multicast socket option:;

• %#_A''_M=M=<!G%#, %#H7_A''_M=M=<!G%#

@ 0oin a multicast group on s specified local

interface+

!truct ip_mreFI

struct in_addr imr_multiaddrJ

struct in_addr imr_interfaceJKJ

!truct ipv7_mreFI

struct in7_addr ipv7mr_multiaddrJ

struct int ipv7mr_interfaceJKJ



multicast socket option:8;

• %#_'<E#_M=M=<!G%#, %#H7_'<E#_M=M=<!G%#

@ leave a multicast group on a specified local

interface+ @ %f the local interface is not specified, the first

matching multicasting group membership is

dropped+




• %#_M$L"%CA!"_%-, %#H7_M$L"%CA!"_%-

@ specif* the interface for outgoing multicast

datagrams sent on this socket+ @ "his interface is specified as either an inaddr

structure for %#v2 or an interface inde. for

%#v7+



multicast socket option:;

• %#_M$L"%CA!"_""L, %#H7_M$L"%CA!"_""L

@ set the %#v2 ""L or the %#v7 hop limit for

outgoing multicast datagrams+ @ %f this is not specified , both default to 1, )hich

restricts the datagram to the local subnet+




• %#_M$L"%CA!"_LEE#, %#H7_M$L"%CA!"_LEE#

@ enable or disable local loopback of multicast

datagrams+ @ 'efault loopback is enabled+

@ "his is similar to broadcasting+



mcast_join and related function

include unp+hint mcast_0oin:int sockfd, const struct sockaddr Daddr, socklen_t salen, const char

Difname, u_int ifinde.;J

int mcast_leave:int sockfd, const struct sockaddr Daddr, socklen_t salen;J

int mcast_set_if:int sockfd, const char Difname, u_int ifinde.;J

int mcast_set_loop:int sockfd, int flag;Jint mcast_set_ttl:int sockfd, int ttl;J

All above return >3 if ok, /1 on error

int mcast_get_if:int sockfd;J

return > nonnegative interface inde. if EO, /1 error

int mcast_get_loop:int sockfd;Jreturn > current loopback flag if EO, /1 error

int mcast_get_ttl:int sockfd;J

return > current ""L or hop limit if EO, /1 error



include Punp+hPinclude Qnet(if+hBint mcast_0oin:int sockfd, const !A Dsa, socklen_t salen, const char Difname, u_int ifinde.;I

s)itch :sa/Bsa_famil*; I

case A-_%N="> Istruct ip_mreF mreFJstruct ifreF ifreFJ

memcp*:RmreF+imr_multiaddr, R::struct sockaddr_in D; sa;/Bsin_addr, sieof:struct in_addr;;J

if :ifinde. B 3; Iif :if_inde.toname:ifinde., ifreF+ifr_name; 66 N$LL; I

errno 6 =NS%EJ (D i(f inde. not found D(return:/1;JKgoto doioctlJK else if :ifname T6 N$LL; Istrncp*:ifreF+ifr_name, ifname, %-NAM!%U;J

doioctl>if :ioctl:sockfd, !%EC&%-A''<, RifreF; Q 3;return:/1;J

memcp*:RmreF+imr_interface, R::struct sockaddr_in D; RifreF+ifr_addr;/Bsin_addr, sieof:struct in_addr;;JK elsemreF+imr_interface+s_addr 6 htonl:%NA''<_ANV;J

return:setsockopt:sockfd, %##<E"E_%#, %#_A''_M=M=<!G%#, RmreF, sieof:mreF;;;JK



ifdef %#H7

case A-_%N="7> I

struct ipv7_mreF mreF7J

memcp*:RmreF7+ipv7mr_multiaddr, R::struct sockaddr_in7 D; sa;/Bsin7_addr,

sieof:struct in7_addr;;J

if :ifinde. B 3;

mreF7+ipv7mr_interface 6 ifinde.J

else if :ifname T6 N$LL;

if : :mreF7+ipv7mr_interface 6 if_nametoinde.:ifname;; 66 3; I

errno 6 =NS%EJ (D i(f name not found D(

return:/1;J

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else

mreF7+ipv7mr_interface 6 3J

return:setsockopt:sockfd, %##<E"E_%#H7, %#H7_A''_M=M=<!G%#,

RmreF7, sieof:mreF7;;;J

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endif

default>

errno 6 =#<E"ENE!$##E<"J

return:/1;J

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include Punp+hPint mcast_set_loop:int sockfd, int onoff;I

s)itch :sockfd_to_famil*:sockfd;; Icase A-_%N="> Iu_char flagJflag 6 onoffJreturn:setsockopt:sockfd, %##<E"E_%#, %#_M$L"%CA!"_LEE#, Rflag, sieof:flag;;;JK

ifdef %#H7case A-_%N="7> Iu_int flagJflag 6 onoffJreturn:setsockopt:sockfd, %##<E"E_%#H7, %#H7_M$L"%CA!"_LEE#, Rflag,sieof:flag;;;JK

endif

default>errno 6 =#<E"ENE!$##E<"Jreturn:/1;JK

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dg_cli function using multicasting

< i i M i t



<eceiving Mone session announcements

• "o receive a multimedia conference on the Mone a

site needs to kno) onl* the multicast address of the

conference and the $'# ports for the conferences

data streams+:audio, video;

• !A#:!ession Announce #rotocol; @ describe the )a*

• !'#:!ession 'escription #rotocol;

@ the contents of these announcements



• A site )ishing to announce a session on the Mbone

@ periodicall* sends a multicast packet containing a description of the session

to a )ell/kno)n multicast group and $'# port

• !ites on Mbone

@ run sdr program

• receives these announcements

• provides an interactive user interface that displa*s the information

• lets user send announcements

• A sample program

@ onl* receives these session announcements to sho) an e.ample of a simple

multicast receiving program



include Punp+hPdefine !A#_NAM= Psap+mcast+netP (D default group name and port D(

define !A#_#E<" P95?Pvoid loop:int, socklen_t;Jint main:int argc, char DDargv;I

int sockfdJconst int on 6 1Jsocklen_t salenJ

struct sockaddr DsaJ

if :argc 66 1;sockfd 6 $dp_client:!A#_NAM=, !A#_#E<", :void DD; Rsa, Rsalen;Jelse if :argc 66 2;sockfd 6 $dp_client:argvX1Y, argvXY, :void DD; Rsa, Rsalen;J

else err_Fuit:Pusage> m*sdr Qmcast/addrB QportB Qinterface/nameBP;J

!etsockopt:sockfd, !EL_!ECO=", !E_<=$!=A''<, Ron, sieof:on;;Jind:sockfd, sa, salen;JMcast_0oin:sockfd, sa, salen, :argc 66 2; Z argvX8Y > N$LL, 3;Jloop:sockfd, salen;J (D receive and print D(e.it:3;J

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"he program receiving the periodic !A#(!'# announcements



include Punp+hP

void loop:int sockfd, socklen_t salen;

I char bufXMASL%N=[1YJ

socklen_t lenJ

ssie_t nJstruct sockaddr DsaJ

struct sap_packet I

uint8_t sap_headerJ

uint8_t sap_srcJ

char sap_dataX1YJ

K DsapptrJ

sa 6 Malloc:salen;J

for : J J ; I

len 6 salenJ

n 6 <ecvfrom:sockfd, buf, MASL%N=, 3, sa, Rlen;J

bufXnY 6 3J (D null terminate D(

sapptr 6 :struct sap_packet D; bufJif : :n /6 D sieof:uint8_t;; Q6 3;

err_Fuit:Pn 6 \dP, n;J

printf:P-rom \s]n\s]nP, !ock_ntop:sa, len;, sapptr/Bsap_data;J

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sending and receiving

• !ends and receives multicast datagrams• -irst part

@ sends a multicast datagram to a specific group

ever* seconds and the datagram contains thesenders hostname and process %'

• !econd part

@ an infinite loop that 0oins the multicast group to)hich the first part is sending and prints ever*

received datagrams



include Punp+hPvoid recv_all:int, socklen_t;Jvoid send_all:int, !A D, socklen_t;J

int main:int argc, char DDargv;I

int sendfd, recvfdJconst int on 6 1Jsocklen_t salenJstruct sockaddr Dsasend, DsarecvJ

if :argc T6 8; err_Fuit:Pusage> sendrecv Q%#/multicast/addressB QportBP;J

sendfd 6 $dp_client:argvX1Y, argvXY, :void DD; Rsasend, Rsalen;Jrecvfd 6 !ocket:sasend/Bsa_famil*, !ECO_'&<AM, 3;J!etsockopt:recvfd, !EL_!ECO=", !E_<=$!=A''<, Ron, sieof:on;;Jsarecv 6 Malloc:salen;Jmemcp*:sarecv, sasend, salen;Jind:recvfd, sarecv, salen;J

Mcast_0oin:recvfd, sasend, salen, N$LL, 3;J

Mcast_set_loop:sendfd, 3;J

if :-ork:; 66 3;recv_all:recvfd, salen;J (D child /B receives D(

send_all:sendfd, sasend, salen;J (D parent /B sends D(K



include Punp+hP

include Qs*s(utsname+hB

define !=N'<A"= (D send one datagram ever* seconds D(

void

send_all:int sendfd, !A Dsadest, socklen_t salen;

I

static char lineXMASL%N=YJ (D hostname and process %' D(

struct utsname m*nameJ

if :uname:Rm*name; Q 3;

err_s*s:Puname errorP;JJ

snprintf:line, sieof:line;, P\s, \d]nP, m*name+nodename, getpid:;;J

for : J J ; I

!endto:sendfd, line, strlen:line;, 3, sadest, salen;J

sleep:!=N'<A"=;J

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include Punp+hP

void

recv_all:int recvfd, socklen_t salen;

I

int nJ

char lineXMASL%N=[1YJ

socklen_t lenJ

struct sockaddr DsafromJ

safrom 6 Malloc:salen;J

for : J J ; I

len 6 salenJ

n 6 <ecvfrom:recvfd, line, MASL%N=, 3, safrom, Rlen;J

lineXnY 6 3J (D null terminate D(

printf:Pfrom \s> \sP, !ock_ntop:safrom, len;, line;J

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!N"#

• N"# 6B so sophisticated protocol

• !N"# 6B simplified version of N"#

@ hosts do not need the comple.it* of a complete N"#

implementation+

@ A client listening for N"# broadcast or multicasts onall attached net)orks and then prints the time

difference bet)een the N"# packet and the hosts

current time/of/da*



define ^AN_19?3 35955533$L (D 19?3 / 1933 in seconds D(struct l'!i(edt ) *+ ,4-bit !i(ed-oint +* uint8_t int_partJ uint8_t fractionJ KJstruct s'!i(edt ) *+ -bit !i(ed-oint +* u_short int_partJ u_short fractionJ KJstruct ntdata ) *+ /P "eader +* u_char statusJ u_char stratumJ u_char ppollJ intprecision>5J struct s_fi.edpt distanceJ

struct s_fi.edpt dispersionJ uint8_t refidJ struct l_fi.edpt reftimeJ struct l_fi.edpt orgJ struct l_fi.edpt recJ struct l_fi.edpt .mtJ KJ

define H=<!%EN_MA!O 3.85define ME'=_MA!O 3.3?

define ME'=_CL%=N" 8define ME'=_!=<H=< 2define ME'=_<EA'CA!"



include Psntp+hP

int main:int argc, char DDargv;

I

int sockfdJchar bufXMASL%N=YJ

ssie_t nJ

socklen_t salen, lenJ

struct ifi_info DifiJ

struct sockaddr Dmcastsa, D)ild, DfromJ

struct timeval no)J

if :argc T6 ; err_Fuit:Pusage> ssntp Q%#addressBP;J

sockfd 6 $dp_client:argvX1Y, PntpP, :void DD; Rmcastsa, Rsalen;J

)ild 6 Malloc:salen;J

memcp*:)ild, mcastsa, salen;J (D cop* famil* and port D(

sock_set_)ild:)ild, salen;J

ind:sockfd, )ild, salen;J(D bind )ildcard D(



ifdef MCA!"

(D 2obtain interface list and process each one D(

for :ifi 6 &et_ifi_info:mcastsa/Bsa_famil*, 1;J ifi T6 N$LLJ ifi 6 ifi/Bifi_ne.t; I

if :ifi/Bifi_flags R %--_M$L"%CA!";

Mcast_0oin:sockfd, mcastsa, salen, ifi/Bifi_name, 3;J

printf:P0oined \s on \s]nP,

!ock_ntop:mcastsa, salen;, ifi/Bifi_name;JK

endif

from 6 Malloc:salen;J

for : J J ; I

len 6 salenJ

n 6 <ecvfrom:sockfd, buf, sieof:buf;, 3, from, Rlen;J

&ettimeofda*:Rno), N$LL;J

sntp_proc:buf, n, Rno);J

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-igure 19+15 : ( ;



include Psntp+h

void sntp_proc:char Dbuf, ssie_t n, struct timeval Dno)ptr;

I

int version, modeJ

uint8_t nsec, useciJ

double usecfJ

struct timeval curr, diffJ

struct ntpdata DntpJ

if :n Q sieof:struct ntpdata;; I

printf:P]npacket too small> \d b*tes]nP, n;J

returnJ

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ntp 6 :struct ntpdata D; bufJ

version 6 :ntp/Bstatus R H=<!%EN_MA!O; BB 8J

mode 6 ntp/Bstatus R ME'=_MA!OJ printf:P]nv\d, mode \d, strat \d, P, version, mode, ntp/Bstratum;J

if :mode 66 ME'=_CL%=N"; I

printf:Pclient]nP;J

returnJ

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nsec 6 ntohl:ntp/B.mt+int_part; / ^AN_19?3J

useci 6 htonl:ntp/B.mt+fraction;J (D 8/bit integer fraction D(

usecf 6 useciJ (D integer fraction /B double D(usecf (6 29297?97+3J (D divide b* DD8 /B X3, 1+3; D(

useci 6 usecf D 1333333+3J (D fraction /B parts per million D(

curr 6 Dno)ptrJ (D make a cop* as )e might modif* it belo) D(

if : :diff+tv_usec 6 curr+tv_usec / useci; Q 3; I

diff+tv_usec [6 1333333J

curr+tv_sec//J

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diff+tv_sec 6 curr+tv_sec / nsecJ

useci 6 :diff+tv_sec D 1333333; [ diff+tv_usecJ (D diff in microsec D(

printf:Pclock difference 6 \d usec]nP, useci;J

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!N"#:;Ene socket per unicast address

Ene socket per broadcast addressEne socket per interface on )hich the multicast group is 0oined



VIII Multicasting Options

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