[zeromq-dev] EGMP and different subnets

Luca Boccassi luca.boccassi at gmail.com
Tue Oct 3 20:00:31 CEST 2017


On Mon, 2017-10-02 at 17:25 +0100, Luca Boccassi wrote:
> On Fri, 2017-09-29 at 20:26 +0000, Yamian Quintero wrote:
> > Hi fellows and thanks for accepting me in your list.
> > 
> > I'm trying to get 0mq sending messages via EPGM using PUB/SUB
> > sockets. I'm using the latest stable release 4.2.2.
> > If both hosts are in the same subnetwork, the messages do flow
> > properly. If the hosts are in different subnets, no message reach
> > the
> > second subnet (no traffic at all is seen in tcpdump on that
> > multicast
> > address).
> > If I use pgmsend/pgmrecv that is built with OpenPGM examples, the
> > messages do reach the second host properly, using the same
> > multicast
> > address and port.
> > My code is just a slightly modified version of the weather server
> > sample.
> > 
> > This is my PUB server:
> > 
> >        void *pub = zmq_socket (ctx, ZMQ_PUB);
> >        char *message_body = (char*)MESSAGE_BODY;
> > 
> > 
> >        rc = zmq_bind (pub,
> > "epgm://192.168.215.99;239.192.1.1:5556");
> >        if (rc != 0){
> >                 cout << "Error: " << zmq_strerror (errno) << "
> > while
> > binding to: " << config.connection_url << endl;
> >                 exit(1);
> >        }
> >        msleep (SETTLE_TIME);
> > 
> >        srand(time(0));
> >        int zip;
> >        int temp;
> >        char *message = new char[255];
> >        while (loop){
> >                 zip = 9999 + (rand()%5);
> >                 temp = (rand()%215) - 80;
> >                 memset((char*)message, 255, 0);
> >                 sprintf(message, "%d %d", zip, temp);
> >                 send_str(pub, message);
> >                 msleep(1000);
> >        }
> > 
> >        delete [] message;
> > 
> > 
> > This is my code for the SUB client:
> > 
> >        void *sub = zmq_socket (ctx, ZMQ_SUB);
> > 
> >        rc = zmq_connect (sub,
> > "epgm://192.168.216.100;239.192.1.1:5556");
> > 
> >        if (rc != 0){
> >                 cout << "Error: " << zmq_strerror (errno) << "
> > while
> > connecting to: " << "epgm://192.168.216.100;239.192.1.1:5556"<<
> > endl;
> >                 exit(1);
> >        }
> >        rc = zmq_setsockopt (sub, ZMQ_SUBSCRIBE, TOPIC,
> > strlen(TOPIC));
> >        if (rc != 0){
> >                 cout << "Error: " << zmq_strerror (errno) << "
> > while
> > subscribing to: " << TOPIC << endl;
> >                 exit(1);
> >        }
> > 
> >        for (int i=0; i<5; i++){
> >          print_str_recv(sub);
> >        }
> > 
> > 
> > The interesting part is what we observe in the routers.
> > 
> > If I use pgmsend/pgmrecv from libpgm-5.2.122, as soon as I start
> > pgmrecv, this is the mroute as seen in the router:
> > 
> > DEV-SW-01#sh ip mroute
> > IP Multicast Routing Table
> > Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C -
> > Connected,
> >        L - Local, P - Pruned, R - RP-bit set, F - Register flag,
> >        T - SPT-bit set, J - Join SPT, M - MSDP created entry,
> >        X - Proxy Join Timer Running, A - Candidate for MSDP
> > Advertisement,
> >        U - URD, I - Received Source Specific Host Report,
> >        Z - Multicast Tunnel, z - MDT-data group sender,
> >        Y - Joined MDT-data group, y - Sending to MDT-data group
> >        V - RD & Vector, v - Vector
> > Outgoing interface flags: H - Hardware switched, A - Assert winner
> > Timers: Uptime/Expires
> > Interface state: Interface, Next-Hop or VCD, State/Mode
> > 
> > (*, 239.192.1.1), 00:00:12/00:02:57, RP 10.222.41.1, flags: SJC
> >   Incoming interface: Null, RPF nbr 0.0.0.0
> >   Outgoing interface list:
> >     Vlan1, Forward/Sparse, 00:00:12/00:02:57
> > 
> > Vlan1 is where the pgmrecv's host is connected to.
> > 
> > When I send a message from the other host, the mroute does have an
> > active source, with the proper incoming interface:
> > 
> > DEV-SW-01#sh ip mroute
> > IP Multicast Routing Table
> > Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C -
> > Connected,
> >        L - Local, P - Pruned, R - RP-bit set, F - Register flag,
> >        T - SPT-bit set, J - Join SPT, M - MSDP created entry,
> >        X - Proxy Join Timer Running, A - Candidate for MSDP
> > Advertisement,
> >        U - URD, I - Received Source Specific Host Report,
> >        Z - Multicast Tunnel, z - MDT-data group sender,
> >        Y - Joined MDT-data group, y - Sending to MDT-data group
> >        V - RD & Vector, v - Vector
> > Outgoing interface flags: H - Hardware switched, A - Assert winner
> > Timers: Uptime/Expires
> > Interface state: Interface, Next-Hop or VCD, State/Mode
> > 
> > (*, 239.192.1.1), 00:02:29/stopped, RP 10.222.41.1, flags: SJC
> >   Incoming interface: Null, RPF nbr 0.0.0.0
> >   Outgoing interface list:
> >     Vlan1, Forward/Sparse, 00:02:29/00:02:08
> > 
> > (192.168.216.100, 239.192.1.1), 00:00:08/00:02:51, flags: T
> >   Incoming interface: Vlan215, RPF nbr 0.0.0.0
> >   Outgoing interface list:
> >     Vlan1, Forward/Sparse, 00:00:08/00:02:51
> > 
> > Vlan215 is where the pgmsend's host is connected to.
> > 
> > 
> > If I repeat this process, using the 0mq-based code, there is
> > something weird happening in the mroute.
> > 
> > When I start the PUB server, the mroute looks just as in the
> > pgmrecv
> > case:
> > 
> > DEV-SW-01#sh ip mroute
> > IP Multicast Routing Table
> > Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C -
> > Connected,
> >        L - Local, P - Pruned, R - RP-bit set, F - Register flag,
> >        T - SPT-bit set, J - Join SPT, M - MSDP created entry,
> >        X - Proxy Join Timer Running, A - Candidate for MSDP
> > Advertisement,
> >        U - URD, I - Received Source Specific Host Report,
> >        Z - Multicast Tunnel, z - MDT-data group sender,
> >        Y - Joined MDT-data group, y - Sending to MDT-data group
> >        V - RD & Vector, v - Vector
> > Outgoing interface flags: H - Hardware switched, A - Assert winner
> > Timers: Uptime/Expires
> > Interface state: Interface, Next-Hop or VCD, State/Mode
> > 
> > (*, 239.192.1.1), 00:00:14/00:02:50, RP 10.222.41.1, flags: SJC
> >   Incoming interface: Null, RPF nbr 0.0.0.0
> >   Outgoing interface list:
> >     Vlan1, Forward/Sparse, 00:00:09/00:02:50
> > 
> > But when I subscribe with the SUB client, the mroute doesn't have
> > the
> > active source, corresponding to it, instead another outgoing
> > interface is added to the wildcarded route:
> > 
> > DEV-SW-01#sh ip mroute
> > IP Multicast Routing Table
> > Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C -
> > Connected,
> >        L - Local, P - Pruned, R - RP-bit set, F - Register flag,
> >        T - SPT-bit set, J - Join SPT, M - MSDP created entry,
> >        X - Proxy Join Timer Running, A - Candidate for MSDP
> > Advertisement,
> >        U - URD, I - Received Source Specific Host Report,
> >        Z - Multicast Tunnel, z - MDT-data group sender,
> >        Y - Joined MDT-data group, y - Sending to MDT-data group
> >        V - RD & Vector, v - Vector
> > Outgoing interface flags: H - Hardware switched, A - Assert winner
> > Timers: Uptime/Expires
> > Interface state: Interface, Next-Hop or VCD, State/Mode
> > 
> > (*, 239.192.1.1), 00:01:31/00:02:53, RP 10.222.41.1, flags: SJC
> >   Incoming interface: Null, RPF nbr 0.0.0.0
> >   Outgoing interface list:
> >     Vlan215, Forward/Sparse, 00:00:06/00:02:53
> >     Vlan1, Forward/Sparse, 00:01:26/00:02:06
> > 
> > 
> > Maybe I'm missing something in the setup of the SUB client socket?
> > Or
> > maybe there is something in the underlying 0mq PGM reciever class
> > that doesn't properly set the multicast parameters?
> > 
> > 
> > Thanks for any help provided,
> > 
> > Yamian.
> 
> I'm absolutely not familiar with the whole PGM/EPGM business, but
> from
> what I can see in all examples, all sockets call zmq_connect, rather
> than zmq_bind.
> 
> If you want to compare the implementation with pgmsend/recv, the
> setup
> is largely done in these 2 functions:
> 
> https://github.com/zeromq/libzmq/blob/master/src/pgm_socket.cpp#L65
> https://github.com/zeromq/libzmq/blob/master/src/pgm_socket.cpp#L117

Also as the manpage says, note that by default ZMQ_MULTICAST_HOPS is 1,
so packets stay on the same network. Did you change that accordingly to
your network setup?

-- 
Kind regards,
Luca Boccassi
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