Could you explain, how switch will forward multicast traffic.For normal unicast traffic it will look into the switch table and make decision on which port to send packet.Can you explain what switch will do incase of multicast traffic.
Depends. Some switches treat multicast as broadcast. Others filter based on multicast subscribers joining using IGMP for IPv4, or MLD for IPv6.
A sender just transmits UDP multicast and receivers join (send membership reports) groups to tell switches to forward the sender's data to them.
Related
Network disconnect issue happens in a system of my company.
Here is the network topolgy:
PC1: two NICs, both static IP address. Data: 10.10.22.11, Control: 10.10.22.10
PC2: two NICs, both static IP address. Data: 10.10.22.101, Control: 10.10.22.100
Default Gateway 10.10.22.11 is set on both side. However I don't think this is necessary, as there is no router or gateway between the two PCs, there directly linked.
A consultant point out, since all the IPs are set in same segment 10.10.22, there could be broadcast storm, which might be the cause of network disconnect.
Is this true? Can broadcast storm happen in directly linked two PCs?
No it shouldn't be.
Broadcast storms happen when there is a loop in a network.
A packet is forwarded to all ports in a switch and if there is a loop the packets are again sent to the same switch on all ports, amplifying the storm, if there is no network loop there shouldn't be any storm.
I don't see any loop in your configuration so this shouldn't be any broadcast storm.
Identifying broadcast storm is not so hard, just sniff on an interface on the network, and if you see millions of times the same broadcast packet, it should be a broadcast storm.
I'm having trouble understanding how multicast addresses work.
First off, is it true that if I have N clients or peers working on separate networks, they all subscribe to the same multicast group, and this group allows any source to send messages, these peers/hosts can all communicate to each other through this group? (sounds like black magic!)
Second, I've heard hints that the IANA controls/regulates the multicast addresses. So do you have to request / ask IANA for a specific multicast address for your project / company? How does this work? Am I mistaken? Can you clarify multicast networking for me?
Thanks much!
Firstly, multicast only works if the routers in the network support it. The IGMP protocol is used for this purpose: http://en.wikipedia.org/wiki/Internet_Group_Management_Protocol. Assuming you have N clients on separate networks connected by multicast capable routers, then they could send messages to a multicast address and other peers that have subscribed to that multicast address will then receive those messages. You can read up further on multicast on Wikipedia.
I think you're confusing IEEE with IANA, the Internet Assigned Numbers Authority (IANA). Have a look at http://www.iana.org/assignments/multicast-addresses/multicast-addresses.xml for multicast address assignments.
Hi All
I ve two PC's A and B which are connected to LAN1 .A is listening on UPNP multicast address 239.255.255.250 .
I have a mobile device D which is connected to a WIFI and the WIFI is connected to LAN1 .
Ip address of PC A is xxx.yyy.209.80 PC B is xxx.yyy.209.81 and device D is xxx.yyy.209.82.
If I send a multicast packet to 239.255.255.250 from PC B it reaches PC A.
But if I send a multicast pakcet from device D it never reaches PC A .Can anyone tell me why ?How to resolve it ?
Thanks in advance
Kozlov
I realize this post is 3 years old but the following information may be useful to someone. I have an iPhone App that uses a 239.x.x.x address and I have issues with certain wireless access points. I found a document that says the following:
There are some special multicast groups, say "well known multicast
groups", you should not use in your particular applications due the
special purpose they are destined to:
224.0.0.1 is the all-hosts group. If you ping that group, all multicast capable hosts on the network should answer, as every
multicast capable host must join that group at start-up on all it's
multicast capable interfaces.
224.0.0.2 is the all-routers group. All multicast routers must join that group on all it's multicast capable interfaces.
224.0.0.4 is the all DVMRP routers, 224.0.0.5 the all OSPF routers, 224.0.013 the all PIM routers, etc. All this special multicast groups are regularly published in the "Assigned Numbers" RFC.
In any case, range 224.0.0.0 through 224.0.0.255 is reserved for local
purposes (as administrative and maintenance tasks) and datagrams
destined to them are never forwarded by multicast routers. Similarly,
the range 239.0.0.0 to 239.255.255.255 has been reserved for
"administrative scoping" (see section 2.3.1 for information on
administrative scoping).
Anyway I changed my address to 238.x.x.x and that did not help with the Netgear R6100 AP. The issue I have seen with Wireshark is that LAN packets are not forwarded to wireless devices. I have not tried the other direction.
Say, for example, that I'm part of a multicast group on 239.255.10.10. I'm also connected to two separate networks, one that has a 192.168.0.* and the other 192.168.1.* addressing. Both networks have a clients that is listening for incoming connections and are part of the above mentioned multicast group (because my client has it hardcoded).
When My computer sends out some data to that multicast group, will it be sent out on both networks or will there be some sort of error?
As long as those clients have registered interest in the group via IGMP, they should both receive the data. However, if there is a router between those networks that the multicast data must traverse, it needs to be configured to pass the data. If your computer is the one connected to both networks, it should just work.
Hi i am on creating streaming application. in that i am using IP Multicasting.
Tell me how to validate the client before adding it in the group.
is that anything i have to do with IGMP?
You don't do it with your application.
IGMP is an internet layer protocol, it may not even reach your application.
Whenever a unit wants to receive multicast to a certain address, it sends an IGMP request to join a group. A router receives the request and remembers that this user wants to belong to this group.
Whenever the router receives a multicast packed destined for that address, it routes it to all the group members, possibly taking some access control restrictions into account.
All group manupulation is performed by routers. You just send your UDP packets to a multicast address (that is 224/4), and the routers decide whether to route it to a subscriber.
If you want to limit destinations where your multicast packets go, you do it on routers.
You should understand though, that the word "routes" above means that the router emits the packet into appripriate interface with a multicast destination address in Ethernet header and multicast destination address in IP header. An Ethernet switch attached to the interface, if any, will distribute the packet over all active ports. Since it knows nothing about internet routing, it will just see the broadcast/multicast bit set in the Ethernet header and act accordingly.
There are, though, some link layer devices (Ethernet switches) who peek into network layer headers and limit multicast to the subscribed units. That is called IGMP snooping. Some of them can also be capable to control access.
OK, there is a legitimate need to control who can join a multicast group. The only way I can see that being done is by filtering IGMP packets inbound on the router interfaces. This would work if the list of "allowed subscribers" is sufficiently static, but if there's a lot of changes, it would rapidly become untenable.
If (and only if) there's administrative control all the way down to a "customer-placed" router, I suspect something could be done there, to limit the groups that device has visibility of, but that is heavily dependent of environment (in a "broadband and multicast video from a single provider" scenario, a contractual requirement for using a provider-managed DSL router would be possible).
In addition to Quassnoi's comments on how multicast works, I have to wonder... Why do you want to restrict multicast membership and/or validate the recipient before having it added to the group?