char databuf[1024] = "Multicast test message lol! After receiving a PIM Null-Register, the RP immediately sends a PIM register stop to acknowledge the reception of the PIM null register message. WebUDP multicast example question. multicast datagram sent with an initial TTL greater than 1 can be Browse other questions tagged. Webbits of the IP multicast group ID are ignored. This is the mroute representing the source entry. Note, if your system is multi-homed you must make sure your multicast traffic is routed out of the correct interface. You can use the script in link below to confirm whether or not the message in tcpdump are displaying as malformed or not ( they are not in my case), https://stackoverflow.com/questions/603852/multicast-in-python, NOTE: I used this script on a debian raspi ( not raspbian and server received packets through router - as setup above - fine), Linux guide : http://stlinux.com/howto/network/short-guide, Cisco : http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/release/12-2_52_se/configuration/guide/3750scg/swmcast.html#wp1024278. In this example, the address is 225.1.1. If the group is in 224.10.15, RP 192.168.0.1 is selected: PIM is included in the FRRouting package. multicast datagrams with initial TTL values as follows: Sites and regions are not strictly defined and sites can be subdivided into destination group and if multicast loopback has not been disabled on the sending Qix - MONICA WAS MISTREATED host has more than one multicast-capable interface. choose the default multicast interface. To show which nexthop is selected for a specific source/group, run the show ip pim nexthop command from the vtysh shell: Multicast boundaries enable you to limit the distribution of multicast traffic by setting boundaries with the goal of pushing multicast to a subset of the network. Be sure to rev2023.3.3.43278. fSii0&$@mNku6 IPV6_MULTICAST_IFSet the device for outgoing multicast packets on the This is allowed only for SOCK_DGRAM and SOCK_RAWsocket. shared port is delivered to all sockets bound to the port. hostilefork / listener.c Last active last week Star 57 Fork 15 Code Revisions 2 Stars 57 Forks 15 Download ZIP Simple listener and sender for UDP multicast Raw listener.c // // Simple listener.c program for UDP multicast // // Adapted from: perror("Setting IP_MULTICAST_LOOP error"); printf("Disabling the loopbackOK.\n"); /* Set local interface for outbound multicast datagrams. More than one process can bind to the same SOCK_DGRAM UDP port if SOCK_DGRAM and SOCK_RAW. An RP is not configured or used. On interface enp0s3, the IP address is postfixed with a /24. is received. /* Receiver/client multicast Datagram example. IGMP version 3 messages are sent to an IGMP v3 specific multicast address, 224.0.0.22. incoming UDP multicast stream stops after fixed time on macOS. Please Bidirectional PIM (BiDir) forwards all traffic through the multicast rendezvous point (RP) instead of tracking multicast source IPs, allowing for greater scale while resulting in inefficient forwarding of network traffic. or for which the sender does not belong to the destination group (such sign in WebThe server listens on TCP Port 19765 by default. You cannot use connection-oriented sockets of type SOCK_STREAM for multicasting. There is no Shared Tree or *,G tree. Revert to If not, then either something is wrong with your server program or possibly kernel settings. Asking for help, clarification, or responding to other answers. There is no additional PIM configuration required to enable SSM beyond enabling PIM and IGMPv3 on the relevant interfaces. transitions from none to the RPF interface of the RP: PIM considers 232.0.0.0/8 the default SSM range. Specify the IP address as INADDR_ANY in order to receive datagrams that are addressed to a multicast group. Multicast datagrams with a TTL greater than one can be delivered However, it would be easier to flag missing requirements in my script if I could look at /proc or sysctl and get the answer. The Oracle Solaris ABI and ABI Tools. Another socket option gives the The G is the multicast group. The multicast router does not forward any multicast datagram with a destination address Configuring Multicast Settings. To configure multicast settings, complete the following steps: 1. Select the global icon, a group, or a SonicWALL appliance. At unit level, the Multicast screen is available only for SonicWALL firewall appliances with SonicOS Enhanced firmware version 2.5 and higher. 2. Expand the Firewall tree and click Multicast. If I run tcpdump, I can see that the packet I am trying to send is actualy sending out data, but I never see anything come through on other machines on the network. IGMP version 3 is the default. memset((char *) &groupSock, 0, sizeof(groupSock)); groupSock.sin_addr.s_addr = inet_addr("226.1.1.1"); /* Disable loopback so you do not receive your own datagrams. to control the scope of the multicasts. This builds an (S,G) state on each multicast router between the RP and FHR. Example of a multicast UDP stream: on the server: sockperf server -i 224.4.4.4 -p 1234 on the client: sockperf ping-pong -i 224.4.4.4 -p 1234 Share Improve this answer Follow edited Mar 30, 2020 at 8:42 Chris 105 5 answered Jan 14, 2014 at 9:40 avner 151 1 3 This doesn't seem to do anything with multicast. Using ip addr instead of ifconfig reports "RTNETLINK answers: File exists" on Debian, Linux "ip route" changes source address of TCP but not UDP, Testing iptables DNAT Rule Locally Using NetCat. This support requires an iptables NFLOG rule to allow nhrpd to intercept multicast packets. Each VRF has its own multicast tree with its own RP(s), sources, and so on. Use the IP_ADD_MEMBERSHIP socket option to join the multicast group that receives the datagrams. The last router in the path, attached to an interested multicast receiver. Apply the custom prefix-list as an ssm-range. a particular group, and the host remains a member of that group until Continue on next ModuleTCP/IP and RAW socket, more program examples. Only IGMPv3 supports requesting a specific source for a multicast group (the sending an S,G IGMP join). The problem in this case was that I had used iptables to only permit traffic from my local subnet 192.168.0.0/24 but of course multicast comes from 224.0.0.0/4 instead. On iptables: Raw. Run the NCLU net show commands to review detailed output for the FHR. every incoming multicast UDP datagram destined to the shared port. if you have multiple interfaces make sure the multicast is routed through the correct one: route add -net 224.0.0.0 netmask 240.0.0.0 dev eth0. But now I need the receiver to run on Ubuntu 10.04. To prevent duplicate multicast packets, a Designated Forward (DF) is elected. What sort of strategies would a medieval military use against a fantasy giant? This can be done in both IGMPv2 and IGMPv3. $ ./mcast_client localInterface.s_addr = inet_addr("203.106.93.94"); if(setsockopt(sd, IPPROTO_IP, IP_MULTICAST_IF, (char *)&localInterface, sizeof(localInterface)) < 0). The hosts that are in the group may reside on a single subnet or may be on different subnets that have been connected by multicast capable routers. WebThe Multicast Source adresses uses normal addresses. More than one socket can claim If Yes, router needs to support the multicasting then. Hosts may join and leave groups at any time. Traditionally, the PIM DR is the only node to send the PIM *,G Join, but to provide resiliency in case of failure, both MLAG switches send PIM *,G Joins towards the RP to receive the multicast stream. The FHR is responsible for the PIM register process. Layer 3 multicast relies on PIM to advertise information about multicast capable routers, and the location of multicast senders and receivers. or for which the sender does not belong to the destination group, should Scan for Open Ports in Linux Transfer Files Between Linux Servers. Examples: Using multicasting with AF_INET Examples: Using multicasting with AF_INET With IP multicasting, an application can send a single IP datagram that a group of hosts in a network can receive. This allows for an increase in both failover and load-balancing throughout. The following command shows that 235.0.0.0 is configured for SPT switchover, identified by pimreg. datagram to a particular socket is determined by the destination port and the To provide meaningful scope control, the multicast routers Tell a multicast router that a multicast receiver no longer wants the multicast group. A tag already exists with the provided branch name. This can be changed with the --listen_port option. The message from multicast server is: "Multicast test message! The Linux socket and network programming on multicasting client-server with C program example. VRFs divide the routing table on a per-tenant basis, ultimately providing for separate layer 3 networks over a single layer 3 infrastructure. Why are incoming packets on a TAP interface seen with tcpdump but not with iptables? Hello all, I have created a UDP multicast transmitter and receiver, first using windows. Multicast Communication Sample in C language on Linux, Source: https://www.tenouk.com/Module41c.html, Example: Sending and receiving a multicast datagram. When a socket of type SOCK_DGRAM is created, an application can use the setsockopt() function to control the multicast characteristics associated with that socket. Very long answer and the tiniest part is what actually appeared to be the problem. The output interface of pimreg can be seen here. */, if(setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse, sizeof(reuse)) < 0), /* Bind to the proper port number with the IP address */. Restarting FRR impacts all routing protocols. Web ip maddr show ~]$ ip maddr show dev br0 8: br0 inet 224.0.0.1 inet6 ff02::1 inet6 ff01::1 [output truncated] ip link show MULTICAST printf("Binding datagram socketOK.\n"); /* Join the multicast group 226.1.1.1 on the local 203.106.93.94 */, /* interface. Initialize a sockaddr_in structure with the destination group IP address and port number. on a single host (such as a router or a mail demon), by IGMP on the router was the problem, but that setting was hidden. WebLinux is, of course (you doubted it? Using the ip command one can check if an interface is multicast capable by: To enable or disable multicast you can use: Thanks for contributing an answer to Unix & Linux Stack Exchange! Multicast Addresses. The full path between LHR and FHR contains an S,G state, although no multicast traffic is flowing. This ability is used IGMP join messages trigger PIM *,G joins. For us we had a similar issue where the multicast group was joined fine, but messages were not being received. socket drops associated memberships when the socket is closed, or when the process cat /boot/config- | grep CONFIG_IP_MULTICAST. When joining a group, specify the class D group address along with the IP address of a local interface. WebSynopsis for Multicast Example Using RDMA_CM and IBV Verbs. Indicates the multicast source and multicast group as well as associated OIFs, IIFs, and RPF information. By default it is set to 1. a membership in the destination group of the datagram. back by the IP layer for local delivery. This does notmean that 2 new system calls were added to support multicast. Is it plausible for constructed languages to be used to affect thought and control or mold people towards desired outcomes? Cumulus Linux MSDP support is primarily for anycast-RP configuration, rather than multiple multicast domains. It is possible to combine multicast sender and receiver in one socat address. compatibility reasons, this delivery does not apply to incoming unicast datagrams. Minimising the environmental effects of my dyson brain, Topological invariance of rational Pontrjagin classes for non-compact spaces. Select the Enable Multicast Routing check box. For ASM, configure a group mapping for a static RP: Each PIM enabled device must configure a static RP to a group mapping and all PIM-SM enabled devices must have the same RP to group mapping configuration. It only takes a minute to sign up. The local IP This code example for Multicast, uses RDMA-CM and VPI (and hence can be run both over IB and over LLE). Allows for the discovery of multicast sources and multicast receivers. I noticed that this can also be a hardware and/or driver problem. Only the 23 least significant bits of the IP The definitions required for the new, multicast-related socket options are found in . If you are redirected to the main page of the user guide, then this page may have been renamed; please search for it there. WebThe kernel in Red Hat Enterprise Linux supports IGMPv3. more than one instance on a single host (such as a conferencing program) There are no restrictions on the location or number of members in a host group. hop limit values. to use Codespaces. The Internet Group Management Protocol (IGMP) enables the administrator to manage routing and subscription to multicast traffic between networks, hosts, and routers. For example: Indicate the groups that a multicast router wants to receive or no longer receive. When you configure an interface, include the pim bfd option. #include . This option provides a performance benefit for applications that have only one instance host's local addresses to choose a particular multicast-capable interface. perror("Reading datagram message error\n"); printf("Reading datagram message from clientOK\n"); [bodo@bakawali testsocket]$ gcc -g mcastserver.c -o mcastserver. To configure a group to never follow the SPT, create the necessary prefix-lists, then configure SPT switchover for the spt-range prefix-list: To view the configured prefix-list, run the vtysh show ip mroute command or the NCLU net show mroute command. For additional information, see RFC 7761 - Protocol Independent Multicast - Sparse Mode. &d:y@t7 %4l'3o:qIP 0(4q*h4JLG15 The * is a wildcard indicating any multicast source. For example OSPF reserves 224.0.0.5 for all OSPF routers and 224.0.0.6 for all Designated Routers. Set the IP_MULTICAST_IF socket option to define the local interface over which you want to send the multicast datagrams. Unicast datagrams are The PIM multicast router for the segment that is listening to the IGMPv3 group receives the IGMP membership join message and becomes an LHR for this group. You can do this in vtysh: To show VRF information, run the NCLU net show mroute vrf command or the vtysh show ip mroute vrf command: You can use bidirectional forward detection (BFD) for PIM neighbors to quickly detect link failures. I know that I can look at CONFIG_IP_MULTICAST in the kernel configuration file to determine whether the kernel was compiled with this. Create an AF_INET, SOCK_DGRAM type socket. WebIn ping (8) replies are sent by the operating system and with omping another instance of omping sends the reply. Each multicast source has a unique SPT. Each multicast router between the LHR and the RP builds a (*,G) mroute with the OIF being the interface on which the PIM join message is received and an Incoming Interface of the reverse path forwarding interface for the RP. Cumulus Linux performs a longest prefix match (LPM) to determine the RP. 224.0.0.0 to 239.255.255.255 as the destination address in a sendto(3SOCKET) call. In Cumulus Linux 4.0 and later the sm keyword is no longer required. When the FHR receives the multicast traffic, it encapsulates it and sends a PIM register to the rendezvous point (RP). To configure the boundary, first create a prefix-list as described above, then run the following commands to configure the IP multicast boundary: You can use the Multicast Source Discovery Protocol (MSDP) to connect multiple PIM-SM multicast domains together, using the PIM-SM RPs. We checked the igmp settings on the router, which seemed to be in order. The following examples enable a socket to send and receive multicast datagrams. Often PIM join/prune messages are described as distinct message types, but are actually a single PIM message with a list of groups to join and a second list of groups to leave. Closing Try putting up another pc listening in group at other end & send data to multicast group & check if receiver at the otherend receives data.Ify,router network does support multicasting.Few tools online: It has been 2 years and we're still using, @oscar but that doesn't mean that it's good to do so as, How can I know if IP Multicast is enabled, How Intuit democratizes AI development across teams through reusability. require the SO_REUSEADDR option to share a single IP protocol type. The message from multicast server is: "Multicast test message lol!". In the following example, if the group is in 224.10.2.5, RP 192.168.0.2 is selected. When receivers want to join a multicast group, join messages are sent along the shared tree towards the RP. How to show that an expression of a finite type must be one of the finitely many possible values? For example: On the RP, no mroute state is created, but the show ip pim upstream output includes the Source and Group: As a receiver joins the group, the mroute output interface on the FHR as a time querying program) should not use this option. There is no shared tree or *,G state. A given socket's receipt of a Pick the local loopback address as the source of the MSDP control packets: Inject the anycast IP address into the IGP of the domain. Before running this multicaster program, you have to run the client program first as in the following. Bulk update symbol size units from mm to map units in rule-based symbology. This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository. Output: You can deliver multicast datagrams with a hop limit that is greater than ", $ ./mcast_server Example: Receiving a multicast datagram, a client. These thresholds prevent datagrams with less than a NOTE: I assume however that servers are listening on port 9131. you didn't provide any info on this. Its arguments are as follows: -4 ' Force usage of IPv4. As the unencapsulated multicast packet travels down the (*,G) tree towards the interested receivers, at the same time, the RP sends a PIM (S,G) join towards the FHR. If you use the ssm-range command, all SSM ranges must be in the prefix-list, including 232.0.0.0/8. */, /* Create a datagram socket on which to receive. */. WebExample: Configuring the Multicast Forwarding Cache When a routing device receives multicast traffic, it places the (S,G) route information in the multicast forwarding cache, inet.1. Real-time Programming and Administration, 13. Source Specific Multicast (SSM) requires multicast receivers to know exactly from which source they want to receive multicast traffic instead of relying on multicast rendezvous points. Specify ipv6_interface to be 0 to Here we present a real working example of a server under CentOS 7, our server has two network ports: eno1 local unicast traffic with local IP eno2 multicast traffic We have multicast TV streams, which we can use through our second network interface and we want to use ffmpeg to encode the video. Is it plausible for constructed languages to be used to affect thought and control or mold people towards desired outcomes? Copyright 2001, 2011, Oracle and/or its affiliates. Is there a single-word adjective for "having exceptionally strong moral principles"? the RP. Everything looked good on the server and the client. To notify the RP that multicast traffic is still flowing when the RP has no receiver, or if the RP is not on the SPT tree, the FHR periodically sends PIM null register messages. Receiving a PIM register stop without any associated PIM joins leaves the FHR without any outgoing interfaces. For PIM-SM, ensure that the unique address is used as the PIM hello source by setting the source: Edit the /etc/network/interfaces file to add an anycast IP address to the loopback interface for each RP in the domain. Multicast routing behaves differently depending on whether the source is sending before receivers request the multicast stream, or if a receiver tries to join a stream before there are any sources. In Cumulus Linux 4.0 and later, the sm keyword is no longer required. The /24 is the CIDR notation and it indicates the value of our netmask. Protocol Independent Multicast (PIM) is a multicast control plane protocol that advertises multicast sources and receivers over a routed layer 3 network. Red Hat Cluster nodes communicate among each other using multicast addresses. Issue the iptables list command. This mean that omping must be running on all computers to test sending/receiving IP multicast/broadcast. The above rule basically determines the Hardware MAC address. The rebalance command might cause some packet loss. How to manage MOSFET spikes in low side switch switch. the default interface by specifying the value 0. Before a host can receive IP multicast datagrams, the host must become a You can change the default SSM group or add additional group ranges to be treated as SSM groups. Traffic is received on one of the MLAG enabled switches. The defined scopes are, where X is unspecified: Node-local scope, restricted to the same node. To troubleshoot this issue, if both PIM and IGMP are enabled, ensure that IGMPv3 joins are being sent by the receiver: Verify that multicast traffic is being received: Verify that PIM is configured on the interface facing the source: If PIM is configured, verify that the RPF interface for the source matches the interface on which the multicast traffic is received: Verify that an RP is configured for the multicast group: An RP does not build an mroute when there are no active receivers for a multicast group, even though the mroute was created on the FHR. Initialize a sockaddr_in structure with the destination group IP address and port number. If you configure equal-cost multipaths (ECMP), PIM chooses the RPF based on the ECMP hash algorithm. The picture below shows us the analysis of the IP address in binary so we can clearly see all the bits: Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and other Un*x-like operating systems. 1 0 obj << /Creator (Microsoft Word) /CreationDate (D:19960514142132Z) /Title () /Author (DWW) /Producer (Acrobat PDFWriter 2.0 for Macintosh) /Keywords () /Subject () /ModDate (D:20030225132949-08'00') >> endobj 2 0 obj [ /PDF /Text ] endobj 3 0 obj << /Pages 124 0 R /Type /Catalog /AcroForm 126 0 R /Metadata 66 2 R >> endobj 4 0 obj << /Type /Page /Parent 5 0 R /Resources << /Font << /F1 6 0 R /F2 7 0 R >> /ProcSet 2 0 R >> /Contents 8 0 R >> endobj 5 0 obj << /Kids [ 4 0 R 10 0 R 14 0 R 17 0 R 20 0 R 23 0 R ] /Count 6 /Type /Pages /Parent 124 0 R >> endobj 6 0 obj << /Type /Font /Subtype /Type1 /Name /F1 /BaseFont /Times-Bold /Encoding /MacRomanEncoding >> endobj 7 0 obj << /Type /Font /Subtype /Type1 /Name /F2 /BaseFont /Times-Roman /Encoding /MacRomanEncoding >> endobj 8 0 obj << /Length 9 0 R /Filter /LZWDecode >> stream group.imr_multiaddr.s_addr = inet_addr("226.1.1.1"); group.imr_interface.s_addr = inet_addr("203.106.93.94"); if(setsockopt(sd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *)&group, sizeof(group)) < 0). The best answers are voted up and rise to the top, Not the answer you're looking for? This special PIM register notifies the RP that a multicast source is still sending, in case any new receivers come online. counterparts, contain explicit scope information that is encoded in the first part of WebIPV6_MULTICAST_HOPSSet the multicast hop limit for the socket. Transport Selection and Name-to-Address Mapping, 12. Binding datagram socketOK. To learn more, see our tips on writing great answers. VRFs on different switches typically connect or are peered over subinterfaces, where each subinterface is in its own VRF, provided MP-BGP VPN is not enabled or supported. WebA process can ask the host to join a multicast group by using the following socket option: struct ip_mreq mreq; setsockopt (sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof (mreq)) where mreq is the structure: struct ip_mreq { struct in_addr imr_multiaddr; /* multicast group to join */ struct in_addr imr_interface; /* interface to join on */ } WebIntroduction This HowTo attempts to give some insight into the basics of setting up multicast routing. The G is the multicast group. that holds the socket is killed. IP_MULTICAST_TTL: Sets the Time To Live (TTL) in the IP header for outgoing multicast datagrams. A special type of PIM register message where the Null-Register flag is set within the packet. To configure PIM, run the following commands: You must enable PIM on all interfaces facing multicast sources or multicast receivers, as well as on the interface where the RP address is configured. to be set to any value from 0 to 255. How to react to a students panic attack in an oral exam? A class D Internet address in the range 224.0.0.1 to 239.255.255.255 identifies a host group. the details of the USB sticks from lsusb: UDP multicast receive does not work: ID 7392:7811 Edimax Technology Co., Ltd EW-7811Un 802.11n Wireless Adapter [Realtek RTL8188CUS], UDP multicast receive works fine: ID 148f:3070 Ralink Technology, Corp. RT2870/RT3070 Wireless Adapter. Therefore, each network switch and associated networking equipment in a Red Hat Cluster must be configured to enable multicast addresses and support IGMP (Internet Group Management Protocol). After the PIM register process is complete and traffic is flowing along the Shortest Path Tree (SPT), either MLAG switch will forward traffic towards the receivers. multicast datagram depends on the socket's associated destination port and memberships, or the When the traffic arrives over the SPT, a PIM (S,G) RPT prune is sent up the shared tree towards the RP. It is a one-to-many transmission method. You can configure SPT switchover on a per-group basis, allowing for some groups to never switch to a shortest path tree; this is also called SPT infinity. For some use-cases, in particular link-local multicast, it may not be possible to use multicast routing, then I recommend trying out: Bridging networks, see subnet, but can be delivered locally if the sending host belongs to the Asking for help, clarification, or responding to other answers. Specify the imr_interface address as INADDR_ANY To access multicast services on a Linux host requires configuring a network interface, a default route for the host, and a route for class D traffic. Styling contours by colour and by line thickness in QGIS. To verify the state of MSDP sessions, run either the NCLU net show msdp mesh-group command or the vtysh show ip msdp mesh-group command: To review the active sources learned locally (through PIM registers) and from MSDP peers, run either the NCLU net show msdp sa command or the vtysh show ip msdp sa command: Authentication, Authorization and Accounting, Hybrid Cloud Connectivity with QinQ and VXLANs, Equal Cost Multipath Load Sharing - Hardware ECMP, Unequal Cost Multipath with BGP Link Bandwidth, Network Switch Port LED and Status LED Guidelines, Monitoring Interfaces and Transceivers Using ethtool, Using NCLU to Troubleshoot Your Network Configuration, Monitoring System Statistics and Network Traffic with sFlow, Simple Network Management Protocol - SNMP, Resource Diagnostics Using cl-resource-query, RFC 7761 - Protocol Independent Multicast - Sparse Mode, TCAM Resource Profiles for Spectrum Switches, Differences between Source Specific Multicast and Any Source Multicast, Multicast Source Discovery Protocol (MSDP). Configuring Linux for Network Multicast The Linux kernel is Level-2 Multicast-Compliant and meets all the requirements to send, receive, or act as a router for multicast packets or datagrams. It also shows that our first three octets are used. Before a host can receive IP multicast datagrams, the host must become a If a multicast datagram is sent to a group to which the How do you get out of a corner when plotting yourself into a corner, ERROR: CREATE MATERIALIZED VIEW WITH DATA cannot be executed from a function. the address. Both static multicast routing, with SMCRoute, and dynamic multicast routing, with mrouted and pimd. the interface driver supports multicasting. A place where magic is studied and practiced? The FHR flag is set on the interface receiving multicast. When the LHR receives the first multicast packet, it sends a PIM (S,G) join towards the FHR to efficiently forward traffic through the network. The Add Multicast Interface dialog box appears. Opening the datagram socketOK. If the network is unnumbered and uses unnumbered BGP as the IGP, avoid using the anycast IP address for establishing unicast or multicast peerings. What is the correct way to screw wall and ceiling drywalls? [root@yourQperfServer ~]# iptables -I INPUT -m tcp -p tcp --dport 19765 -j ACCEPT && iptables -I INPUT -m tcp -p tcp --dport 19766 -j ACCEPT. Since 4.2 BSD On server side, start a packet capture : tcpdump -i host 239.255.250.250
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