Multicast UDP deamon and VLAN interfaces - TCP-IP

This is a discussion on Multicast UDP deamon and VLAN interfaces - TCP-IP ; Hi guys, I have a daemon running on Debian and listening for multicast packets sent to 224.0.0.251:5353 (ZeroConf Multicast DNS queries). The server is plugged into a VLAN trunk with eth0 and joins several VLANs using virtual interfaces (i.e. eth0.xxx). ...

+ Reply to Thread
Results 1 to 6 of 6

Thread: Multicast UDP deamon and VLAN interfaces

  1. Multicast UDP deamon and VLAN interfaces

    Hi guys,
    I have a daemon running on Debian and listening for multicast packets
    sent to 224.0.0.251:5353 (ZeroConf Multicast DNS queries).
    The server is plugged into a VLAN trunk with eth0 and joins several
    VLANs using virtual interfaces (i.e. eth0.xxx). It should be able to
    capture the UDP packets on any interfaces, so it spawns a thread for
    each interface specified in a config file, and for each thread it
    creates a socket:

    /************************************************** ************************************/
    // Inside a function whose parameters are:
    // int *sfd - the socket file descriptor
    // struct in_addr bound_ip - the IP on which to listen

    #define PORT 5353
    #define MGRP "224.0.0.0.251"

    struct sockaddr_in addr;
    struct ip_mreq mc;

    *sfd = socket( AF_INET, SOCK_DGRAM, IPPROTO_UDP );

    bzero( &addr, sizeof( addr ) );
    addr.sin_family = AF_INET;
    addr.sin_port = htons( PORT );
    addr.sin_addr = bound_ip;

    bind( *sfd, (struct sockaddr *) &addr, sizeof(addr));

    int flag = 1;
    mc.imr_multiaddr.s_addr = inet_addr( MGRP );
    mc.imr_interface = bound_ip;

    setsockopt( *sfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mc, sizeof(mc));
    setsockopt( *sfd, SOL_SOCKET, SO_REUSEADDR, (char *) &flag,
    sizeof(flag));
    setsockopt( *sfd, SOL_SOCKET, SO_REUSEPORT, (char *) &flag,
    sizeof(flag));

    /************************************************** ************************************/

    The problem is that the server captures the UDP packets sent to the
    Multicast group only when bound_ip is set to 0 (INADDR_ANY), and even
    then, only when the packets are coming on the first interface (eth0).

    If I see right, the problem could be that I want to capture packets
    sent to 224.0.0.251 while listening on IP, say, 192.168.2.103. But even
    then, how could one specify on which interface to listen for a
    Multicast packet?

    What I'd like is to
    - be able to specify several interfaces and spawn one daemon for each
    one
    - receive Multicast UDP packets only on the specified interfaces

    Any hints are appreciated

    Thank you,

    Regards


  2. Re: Multicast UDP deamon and VLAN interfaces


    pietro.cerutti@gmail.com wrote:

    > Hi guys,
    > I have a daemon running on Debian and listening for multicast packets
    > sent to 224.0.0.251:5353 (ZeroConf Multicast DNS queries).
    > The server is plugged into a VLAN trunk with eth0 and joins several
    > VLANs using virtual interfaces (i.e. eth0.xxx). It should be able to
    > capture the UDP packets on any interfaces, so it spawns a thread for
    > each interface specified in a config file, and for each thread it
    > creates a socket:
    >
    > /************************************************** ************************************/
    > // Inside a function whose parameters are:
    > // int *sfd - the socket file descriptor
    > // struct in_addr bound_ip - the IP on which to listen
    >
    > #define PORT 5353
    > #define MGRP "224.0.0.0.251"
    >
    > struct sockaddr_in addr;
    > struct ip_mreq mc;
    >
    > *sfd = socket( AF_INET, SOCK_DGRAM, IPPROTO_UDP );
    >
    > bzero( &addr, sizeof( addr ) );
    > addr.sin_family = AF_INET;
    > addr.sin_port = htons( PORT );
    > addr.sin_addr = bound_ip;
    >
    > bind( *sfd, (struct sockaddr *) &addr, sizeof(addr));
    >
    > int flag = 1;
    > mc.imr_multiaddr.s_addr = inet_addr( MGRP );
    > mc.imr_interface = bound_ip;
    >
    > setsockopt( *sfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mc, sizeof(mc));
    > setsockopt( *sfd, SOL_SOCKET, SO_REUSEADDR, (char *) &flag,
    > sizeof(flag));
    > setsockopt( *sfd, SOL_SOCKET, SO_REUSEPORT, (char *) &flag,
    > sizeof(flag));
    >
    > /************************************************** ************************************/
    >
    > The problem is that the server captures the UDP packets sent to the
    > Multicast group only when bound_ip is set to 0 (INADDR_ANY), and even
    > then, only when the packets are coming on the first interface (eth0).


    UNIX® Network Programming Volume 1 by R.W.Stevens says:

    If the local interface is specified as the wildcard address for IPv4
    (INADDR_ANY) or as an index of 0 for IPv6, then a single local
    interface is chosen by the kernel.

    > If I see right, the problem could be that I want to capture packets
    > sent to 224.0.0.251 while listening on IP, say, 192.168.2.103. But even
    > then, how could one specify on which interface to listen for a
    > Multicast packet?
    >
    > What I'd like is to
    > - be able to specify several interfaces and spawn one daemon for each
    > one
    > - receive Multicast UDP packets only on the specified interfaces


    man ip(7)

    IP_ADD_MEMBERSHIP
    Join a multicast group. Argument is an ip_mreqn
    structure.

    struct ip_mreqn {
    struct in_addr imr_multiaddr; /* IP multicast group
    address */
    struct in_addr imr_address; /* IP address of local
    interface */
    int imr_ifindex; /* interface index */
    };

    imr_multiaddr contains the address of the multicast
    group the
    application wants to join or leave. It must be a valid
    multi-
    cast address. imr_address is the address of the local
    interface
    with which the system should join the multicast group; if
    it is
    equal to INADDR_ANY an appropriate interface is chosen
    by the
    system. imr_ifindex is the interface index of the
    interface
    that should join/leave the imr_multiaddr group, or 0 to
    indicate
    any interface.

    For compatibility, the old ip_mreq structure is still
    supported.
    It differs from ip_mreqn only by not including the
    imr_ifindex
    field. Only valid as a setsockopt(2).


  3. Re: Multicast UDP deamon and VLAN interfaces

    pietro.cerutti@gmail.com wrote:
    >
    > I have a daemon running on Debian and listening for multicast packets
    > sent to 224.0.0.251:5353 (ZeroConf Multicast DNS queries).
    > The server is plugged into a VLAN trunk with eth0 and joins several
    > VLANs using virtual interfaces (i.e. eth0.xxx). It should be able to
    > capture the UDP packets on any interfaces, so it spawns a thread for
    > each interface specified in a config file, and for each thread it
    > creates a socket:


    Off topic. C knows nothing about multicast, servers, eth0, VLANs,
    UDP, packets, threads, sockets, etc. Find a newsgroup that deals
    with your system. comp.unix.programmer is one possibility, another
    is something that has 'debian' in its name.

    --
    Some informative links:








  4. Re: Multicast UDP deamon and VLAN interfaces


    Maxim Yegorushkin ha scritto:

    > pietro.cerutti@gmail.com wrote:


    > man ip(7)


    > struct ip_mreqn {
    > struct in_addr imr_multiaddr; /* IP multicast group
    > address */
    > struct in_addr imr_address; /* IP address of local
    > interface */
    > int imr_ifindex; /* interface index */
    > };


    Ok, i passed from ip_mreq to ip_mreqn, but that wasn't my problem:
    it seems that the interface doesn't even join the multicast group:

    Using this:
    struct ip_mreqn mc;
    mc.imr_multiaddr = conf.multicast_group;
    mc.imr_address = bound_ip;
    mc.imr_ifindex = 0;
    setsockopt( *sfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mc, sizeof(mc))

    I still can't see any packet come into the daemon, even when netcat'ing
    to 224.0.0.251:5353 using UDP.
    # nc -u 224.0.0.251 5353

    It just seems that the daemon doesn't capture packets sent to the
    multicast group.

    Thanx in advance,


  5. Re: Multicast UDP deamon and VLAN interfaces


    pietro.cerutti@gmail.com wrote:

    > Maxim Yegorushkin ha scritto:
    >
    > > pietro.cerutti@gmail.com wrote:

    >
    > > man ip(7)

    >
    > > struct ip_mreqn {
    > > struct in_addr imr_multiaddr; /* IP multicast group
    > > address */
    > > struct in_addr imr_address; /* IP address of local
    > > interface */
    > > int imr_ifindex; /* interface index */
    > > };

    >
    > Ok, i passed from ip_mreq to ip_mreqn, but that wasn't my problem:
    > it seems that the interface doesn't even join the multicast group:
    >
    > Using this:
    > struct ip_mreqn mc;
    > mc.imr_multiaddr = conf.multicast_group;
    > mc.imr_address = bound_ip;
    > mc.imr_ifindex = 0;
    > setsockopt( *sfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mc, sizeof(mc))


    Your new code is equivalent to the code you posted before. What happens
    is that you let the kernel determine which one interface joins the
    group. This is why you receive datagrams from one interface only. To
    join a multicast group on a specific interface set imr_address as the
    local address of that interface, rather than INADDR_ANY.

    > I still can't see any packet come into the daemon, even when netcat'ing
    > to 224.0.0.251:5353 using UDP.
    > # nc -u 224.0.0.251 5353
    >
    > It just seems that the daemon doesn't capture packets sent to the
    > multicast group.


    Use netstat -gn to see which interface joined which group.


  6. Re: Multicast UDP deamon and VLAN interfaces

    CBFalconer writes:
    > pietro.cerutti@gmail.com wrote:
    >> I have a daemon running on Debian and listening for multicast packets
    >> sent to 224.0.0.251:5353 (ZeroConf Multicast DNS queries).
    >> The server is plugged into a VLAN trunk with eth0 and joins several
    >> VLANs using virtual interfaces (i.e. eth0.xxx). It should be able to
    >> capture the UDP packets on any interfaces, so it spawns a thread for
    >> each interface specified in a config file, and for each thread it
    >> creates a socket:

    >
    > Off topic. C knows nothing about multicast, servers, eth0, VLANs,
    > UDP, packets, threads, sockets, etc. Find a newsgroup that deals
    > with your system. comp.unix.programmer is one possibility, another
    > is something that has 'debian' in its name.


    Note that this thread is also cross-posted to comp.unix.programmer,
    comp.protocols.tcp-ip, and comp.os.linux.networking. But yes, it's
    off-topic for comp.lang.c.

    --
    Keith Thompson (The_Other_Keith) kst-u@mib.org
    San Diego Supercomputer Center <*>
    We must do something. This is something. Therefore, we must do this.

+ Reply to Thread