28 votes
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Is multicast on the public internet possible? And if yes: How?

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 ...
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  • 93.5k
23 votes
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Why isn't multicasting more popular?

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 ...
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  • 15.6k
21 votes
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What are the benefits and cons of IGMP snooping?

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 ...
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  • 29.6k
17 votes

Is multicast on the public internet possible? And if yes: How?

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 ...
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  • 541
13 votes
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Is multicast possible in tcp?

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 ...
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  • 29.6k
13 votes

Why isn't multicasting more popular?

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 ...
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  • 11.6k
12 votes

Can I truly multicast over WIFI?

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 ...
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11 votes
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why TTL value 1 in IGMP

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.
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11 votes
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What is the correct mask to use with 224.0.0.0?

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 ...
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11 votes
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Can I truly multicast over WIFI?

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 ...
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  • 134
9 votes

Why we use 224 as multicast address in many protocols?

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....
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  • 261
9 votes

OSPF and its use of Multicast

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 ...
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8 votes
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What is the advantage of multicasting in IPv6 (compared to broadcast)?

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 ...
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8 votes

What are real life examples of broadcast and multicast?

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 ...
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7 votes
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MLD messages during IPv6 duplicate address detection

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 ...
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7 votes

What is the difference between Unicast RPF and Reverse Path Forwarding?

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 ...
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7 votes
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Why is MBGP needed?

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,...
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  • 156
7 votes
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Multicast between VLANs

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. ...
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7 votes
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Can communication to broadcast 224.0.0.1 be made to reach hosts outside of the local subnet?

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 ...
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7 votes
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Layering unicast addressing over multicasts

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 ...
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6 votes
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overcome microbursts in cisco router or transmitting linux machine

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 ...
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6 votes

Is multicast possible in tcp?

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 ...
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6 votes
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Is the real broadcasting on internet possible

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 ...
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6 votes
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Why is the NDP Neighbor Solicitation message sent to the solicited-node address?

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 ...
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  • 93.5k
5 votes
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IPv6 Multicast - Purposes for the Interface-Local scope?

Node-local scope is mostly useful for inter-process communication. The sender and receiver can be different processes on the same node.
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5 votes
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RIP V2 multicasting looks as broadcasting at IP add 224.0.0.9

224.0.0.9 is a protocol standard multicast address, meaning that it is reserved for all RIPv2 speaking routers. This reduces unnecessary overhead, and only speaks to RIPv2 routers, instead of a full ...
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5 votes

How do I mcast multiple pcap files simultaneously with guaranteed ordering and controllable speed?

My thoughts on this are that firstly if you capture the traffic in one place (if you are able to, if you have one capture machine/device joint to both mcast groups) you don't have the complexity of ...
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  • 5,270
5 votes

why TTL value 1 in IGMP

TTL == 1 means stay on this network; it will not be forwarded by any router. This is true of multicast and unicast. The purpose for doing this with multicast is to limit how far the message can spread....
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  • 29.6k
5 votes
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KEMP load balancers using UCARP (VRRP) - multicast MAC address not being picked up

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 ...
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