Hello everybody,
for testing purposes I need to modify the source address
of IGMP V2 membership report messages. I gave my machine
an additional IP address and a route to a local router
192.168.213.1 (for testing):
fook:/home/penz # ip addr
1: lo: <LOOPBACK,UP> mtu 16436 qdisc noqueue
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 brd 127.255.255.255 scope host lo
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 1000
link/ether 00:e0:18:a6:7b:dc brd ff:ff:ff:ff:ff:ff
inet 137.226.12.188/24 brd 137.226.12.255 scope global eth0
inet 192.168.213.188 peer 192.168.213.1/32 scope global eth0
inet6 fe80::2e0:18ff:fea6:7bdc/64 scope link
valid_lft forever preferred_lft forever
3: sit0: <NOARP> mtu 1480 qdisc noqueue
link/sit 0.0.0.0 brd 0.0.0.0
fook:/home/penz # route
Kernel IP Routentabelle
Ziel Router Genmask Flags Metric Ref Use
Iface
192.168.213.1 * 255.255.255.255 UH 0 0 0
eth0
192.168.213.0 192.168.213.1 255.255.255.0 UG 0 0 0
eth0
137.226.12.0 * 255.255.255.0 U 0 0 0
eth0
link-local * 255.255.0.0 U 0 0 0
eth0
loopback * 255.0.0.0 U 0 0 0 lo
default routus.informat 0.0.0.0 UG 0 0 0
eth0
Now when an application joins a multicast group on interface
192.168.213.188,
an IGMP membership report is sent, but with source address 137.226.12.188.
I wrote a little test routine (see below) and wonder how the source address
for IGMP packets is chosen by the kernel. For my purpose I need the source
address 192.168.213.188. Can anybody tell me how to set this up?
Thanks in advance,
Stefan
Test routine:
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define RESERVED_PORT 50427
#define MCAST_ADDR "239.255.254.253"
#define IF_ADDR "192.168.213.188"
int main() {
int sockfd;
struct ip_mreq mreq;
struct sockaddr_in mysockaddr;
struct in_addr ifaddr;
memset(&mysockaddr, 0, sizeof(mysockaddr));
mysockaddr.sin_family = AF_INET;
mysockaddr.sin_port = htons(RESERVED_PORT);
mysockaddr.sin_addr.s_addr = inet_addr(MCAST_ADDR);
memset(&ifaddr, 0, sizeof(ifaddr));
ifaddr.s_addr = inet_addr(IF_ADDR);
sockfd = socket(PF_INET, SOCK_DGRAM, 0);
bind(sockfd,
(struct sockaddr *) &mysockaddr,
sizeof(mysockaddr));
memcpy(&mreq.imr_multiaddr, &(mysockaddr.sin_addr), sizeof(struct
in_addr));
memcpy(&mreq.imr_interface, &ifaddr, sizeof(struct in_addr));
setsockopt(sockfd,
IPPROTO_IP,
IP_MULTICAST_IF,
&ifaddr,
sizeof(ifaddr));
setsockopt(sockfd,
IPPROTO_IP,
IP_ADD_MEMBERSHIP,
&mreq,
sizeof(mreq));
sleep(2);
return 0;
}
--
Dipl.-Inform. Stefan Penz
Aachen University of Technology
Computer Science Department
Informatik IV (Communication and Distributed Systems)
Ahornstr. 55, D-52074 Aachen, Germany
Tel.: +49 (241) 80-21424
Fax: +49 (241) 80-22220
EMail: penz@cs.rwth-aachen.de
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