28

You cannot multicast on the public Internet, but you can multicast across the public Internet to another site by using a tunnel that supports multicast. Multicast routing is very different from unicast routing, and all the routers in the path of the multicast packets need to have multicast routing configured.


23

Because multicast is one source to many receivers, and thus two way communications (and anything using TCP connections) won't work. That makes it unfit to use for teleconferencing, online collaboration and many more applications. Streaming media would work, but many people like to be able to pause the stream for example, and that wouldn't be possible with ...


20

IGMP Snooping is a feature for switches to learn what multicast groups are needed on which ports. Routers not handling multicast routing don't care. That said, without an mrouter in the network, you need to configure one (or more) igmp queriers. This ensures group membership reports are flood through the network periodically to keep the forwarding ...


17

As an end-user, you cannot multicast across the Internet, unless using a tunnel. As a larger organization, like a video provider or an ISP, it is certainly possible to forward multicast packets across their domain boundary (i.e. across an Internet). How ? Essentially, to forward multicast packets within your own domain (or Autonomous System, AS), you use ...


17

Because 224.0.0.0/24 is the range assigned by IANA for local multicast - Local Network Control Block. Addresses in this range are non-routable, they can only exist on a link, and cannot be forwarded by a router. These protocols only require multicast to operate within a single link, often to provide dynamic neighbour discovery and flooding of protocol ...


13

In a word: NO Multicast is a one-to-many system. TCP requires a one-to-one handshake to synchronize counters (sequence numbers) to ensure reliable transport. This cannot be done with many receivers as the sender has no way to know how many receivers there are and thus how many ACKs to expect, or what to do if one of the receivers disappears mid-transfer, ...


13

Multicast is one of those ideas that sounds nice in principle but doesn't really scale to a network like the internet. It requires routers to keep track of a bunch of extra state, has significant potential for denial of service attacks and also has significant problems from a billing perspective. The result of this is that ISPs generally said no to multicast....


12

As I understand Wifi, it can never true multicast, as each device holds a '1:1" relationship with the AP, and then receives the same packet... then the next device connects and gets the same packet. Your understanding is flawed. Multicast does exist, but like most management traffic on a wireless network it must run at the lowest supported base/basic/...


11

The reason that it doesn't have to leave the LAN is that IGMP (or MLD if you use IPv6) only talks to the multicast router on the LAN. The multicast router will take care of the routing.


11

You can't use any addresses from 224.0.0.0 (except for multicast) through 255.255.255.254, and 255.255.255.255 is a Limited Broadcast address. Multicast addresses are 224.0.0.0/4. Masks are not used in multicast; you subscribe, individually, to multicast groups. Reserved addresses are 240.0.0.0/4. While named "Class E" in the old class routing ...


11

Lets test this out then. If we send multicast packets to multiple devices connected to a WiFi access point at a constant rate, then the access point should report the same amount of traffic. To run this test, I'm sending packets from a wired PC to an an android tablet and a raspberry pi. Don't have any iOS devices. The network testing tool iperf can easily ...


9

Outside of Karl's explanation, it's a holdover from the original class-based IP addressing scheme. As you know, the classes were as follows (based on the first octet): Class A (0xxxxxxx): [0-127].0.0.0/8 Class B (10xxxxxx): [128.0-191.255].0.0/16 Class C (110xxxxx): [192.0.0-223.255.255].0/24 Class D (1110xxxx): 224.0.0.0-239.255.255.255 Class E (1111xxxx): ...


9

The benefit of multicast is that hosts not subscribing to the multicast group ignore frames they receive that are sent to the multicast group. With broadcast, they cannot ignore the frames. The OSPF multicast group is a link-local multicast that gets sent to every switch interface, even with IGMP snooping enabled on the switch. OSPF only uses multicast on ...


8

Switches without MLD or IGMP snooping will treat multicast and broadcast (if there were broadcast in IPv6) the same -- namely, they would flood the packets out all ports. But the second half of your statement, "and therefore negate the benefits of multicast" doesn't follow. The advantages of multicast are not for the switch. They are for the end ...


8

Broadcasts are stopped at a layer-3 boundary (router). An example of a broadcast is an ARP request where a host is looking for the MAC address of the owner of an IP address. The host sends a broadcast asking, "Who owns this IP address?" Broadcasts are received and processed by every host in the layer-2 domain. A multicast is received and processed by hosts ...


7

Background I am somewhere that blocks Dropbox downloads, so I can't see the captured traffic, but I'll go on the assumption these were 64-byte ethernet multicasts. Let's do some math to see how much traffic you're permitting... A 64-byte frame is 672 bits (including 8 bytes for Preamble/SFD, and 12 bytes for IFG)... 8*(8 + 12 + 64) = 672 bits That means line ...


7

Key to answering your question is making a very important distinction: Duplicate Address Detection (DAD) and Multicast Listener Discovery (MLD) are completely separate protocols. Now, that said, I think this paragraph of RFC2710 explains the "duplicate" transmission: When a node starts listening to a multicast address on an interface, it should ...


7

Both Reverse Path Forwarding and Unicast Reverse path Forwarding do basically the same thing: Verify that the data is coming from the same direction you would expect it to come from. Their function is slightly different though: 'Normal' RPF will check the source of multicast traffic, to avoid network loops. uRPF will check the source of unicast traffic, to ...


7

MBGP or Multiprotocol BGP extensions The first BGP specification was published in 1989, well before IPv6 was created and only shortly after multicast was added to IPv4. Even BGP-4 doesn’t support IPv6, multicast or VPNs. Until 1998, that is, when RFC 2283 introduced the multiprotocol extensions. These allow BGP to handle routing information for arbitrary &...


7

VLANs logically break a switch into multiple, unconnected switches. There is no traffic between VLANs (layer-2), except through a router (layer-3). By default, routers do not route multicast packets. Multicast routing is very different than unicast routing, and it must be specifically configured on all the routers between networks in order for multicast ...


7

Can communication to broadcast 224.0.0.1 be made to reach hosts outside of the local subnet? First, that is a multicast group, not a broadcast address. Next, the multicast address is in the Local Network Control Block (224.0.0.0/24), and multicasts sent to groups in that block are limited to the network on which they originate. So given the above example, ...


7

First part of the question is whether there is a standard that prohibits use of IPv4 unicast addresses with multicast MAC address in an ethernet frame ? The problem here is that you are dealing with two different standards on different network layers that are defined and maintained by two completely different groups. Ethernet is IEEE 802.3, but IP is ...


6

Yes, it's possible. But you would have to advertise a /24 network (or larger), based on current Internet routing policies. So if your name server IP was 1.2.3.4, you would have to advertise 1.2.3.0/24 from each of your locations. The rest of the addresses in that subnet would be, practically speaking, wasted. You also would have to have your own provider-...


6

My questions are: Should we setup on our core network switch OSPF with a router ID of 1.1.1.1 and then not set any OSPF settings on any other switch? OSPF is not necessary for this implementation. Would PIM Sparse Mode only need to be enabled on the core switches or on all of the switches in the network? Pim-SM needs to be enabled on each L3 ...


6

So first of all show fabric utilization all shows fabric utilization, not CPU utilization. Fabric doesn't have CPU component per se, and you can go all up to 100% of fabric utilization without any adverse effects similar to what CPU causes when nearing to the full load. Next, the WS-X6548-GE-TX is 8Gbit/s card, so "old" fabric attached LC with 8Gbit/s ...


6

No. Even though TCP is composed of two separate sender/receiver relationships, the communication needs to be one-to-one and bidirectional. But there are protocols which implement reliable transport over multicast, but they often use an inverse tree (publisher becomes consumer, and vice-versa) for negative acknowledgements. They are very different from TCP.


6

I don't think you really understand that the Internet is just a collection of many ISPs which connect to other ISPs. Each ISP has its own policies. Also, IP has a single source and a single destination address for each IP packet. Actual broadcasts, from the perspective of IP (broadcast destination address), are restricted to a single broadcast domain, and a ...


6

I don't think you quite understand that Alice needs Bob's MAC address before she can send anything to him. What RFC 4861, Neighbor Discovery for IP version 6 (IPv6) says: 4.3. Neighbor Solicitation Message Format Nodes send Neighbor Solicitations to request the link-layer address of a target node while also providing their own link-layer address to the ...


5

Node-local scope is mostly useful for inter-process communication. The sender and receiver can be different processes on the same node.


5

I was able to resolve the issue. On the Kemp (with HA pair) you have the option of using a "Virtual MAC Address". If this box isn't checked, then the MAC of a load balancer VIP is that of the physical interface of the active Kemp unit. If this box is checked, then the MAC address of the VIP is a VRRP MAC. As you mentioned above the VRRP RFC states that the ...


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