31 votes
Accepted

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 ...
Ron Maupin's user avatar
  • 99.6k
24 votes
Accepted

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 ...
Teun Vink's user avatar
  • 17.3k
19 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 ...
pHeoz's user avatar
  • 590
14 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 ...
YLearn's user avatar
  • 27.3k
14 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 ...
Peter Green's user avatar
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12 votes
Accepted

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 ...
Twiske's user avatar
  • 144
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....
ErikF's user avatar
  • 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 ...
Ron Maupin's user avatar
  • 99.6k
7 votes
Accepted

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,...
Noction's user avatar
  • 166
7 votes
Accepted

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. ...
Ron Maupin's user avatar
  • 99.6k
7 votes
Accepted

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 ...
Ron Maupin's user avatar
  • 99.6k
7 votes
Accepted

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 ...
Ron Maupin's user avatar
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6 votes
Accepted

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 ...
Ron Maupin's user avatar
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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 ...
Ron Maupin's user avatar
  • 99.6k
6 votes
Accepted

Defining what type of casting based on IPv4 address

For IPv4, unicast addresses are in the 0.0.0.0 to 223.255.255.255 range*, multicast addresses are in 224.0.0.0 to 239.255.255.255 address range. *Broadcast addresses are more complicated. There is ...
Ron Maupin's user avatar
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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 ...
Ed Smith's user avatar
5 votes

How is Multicast IP mapped to Multicast Mac address?

The 01-00-5E is commonly called the OUI (Organizationally Unique Identifier), which the IEEE (the group which assigns them) calls MA-L (MAC Address Block Large). Don't read a lot more into it than ...
Ron Maupin's user avatar
  • 99.6k
5 votes

Why is MBGP needed?

One of the most important thing for Multicast protocol is RPF (Reverse Path Forwarding) - this is the feature which would check and make sure that for a coming multicast packet (sent by a multicast ...
Noction's user avatar
  • 166
5 votes

Private Public and Special IP addressing

No. IPv4 addresses in the range 224.0.0.0/4 are not regular addresses; they are multicast addresses. Multicast is normally confined to a single LAN. Multicast routing must be enabled on all the ...
Ron Maupin's user avatar
  • 99.6k
5 votes

Multicast between VLANs

There is no inter-VLAN communication without a router. Multicasts are not usually routed - unless your router is specifically configured to do so.
Zac67's user avatar
  • 84.4k
5 votes
Accepted

Network flooded with ICMPv6 Multicast Listener Report Packets

You wouldn't be looking for ARP entries with IPv6, since ARP doesn't exist with IPv6. You would be looking for IPv6 ICMP Neighbor Discovery cache. IPv6 MLD messages are used similarly to IPv4's IGMP ...
HostBits's user avatar
  • 636
5 votes
Accepted

How do hosts subscribe to multicast addresses?

An IP multicast router (usually that's a switch) announces available groups using membership queries. A host subscribes to some of these groups by sending a membership report. Unsubscribing works by ...
Zac67's user avatar
  • 84.4k
5 votes

What's so special about the multicast address range?

Basically, you need to draw a clear line between unicast, broadcast and multicast traffic because it needs to be treated (very) differently. The convention is to use a special address range. Another ...
Zac67's user avatar
  • 84.4k
5 votes

Forward Avahi mDNS packets from one network to another

Zeroconf Networking RFC 6272, RFC 6273 has the fundamental design constraint of being "local subnet only". Zeroconf's multicast packets have a TTL of 255, and if you try forward these ...
Marc 'netztier' Luethi's user avatar
5 votes
Accepted

If a switch doesn't support multicast, are multicast packets simply flooded out all ports?

Multicast is a special case of broadcast. If a switch does not have any specific handling for multicast (eg. igmp snooping), multicast traffic is simply broadcast, and floods to all ports.
Ricky's user avatar
  • 32.2k
5 votes

What does 'moving packets away from the source' in RPF means?

RPF is one tool in your toolbox to help keep your network safe. RPF is used to verify that packets are coming from the direction of a reachable source. This helps to prevent malicious packets from ...
Ron Maupin's user avatar
  • 99.6k
4 votes

Is the real broadcasting on internet possible

Many places, such as television and radio stations, do "broadcast" live programming over the Internet. The problem they all have is a matter of scale. Every connection (listener) requires a ...
Ron Trunk's user avatar
  • 67.5k
4 votes

How is Multicast IP mapped to Multicast Mac address?

An IP host group address is mapped to an Ethernet multicast address by placing the low-order 23-bits of the IP address into the low-order 23 bits of the Ethernet multicast address 01-00-5E-00-00-00 (...
Everton's user avatar
  • 1,636
4 votes

Inter-switch IGMP on a VLAN with two switches, and a multicast source per switch

This is an all too common problem. Snooping requires either a full multicast router, or an igmp querier in the network (one per broadcast domain.) Both periodically send out multicast group requests ...
Ricky's user avatar
  • 32.2k

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