1. Ipv6 Multicast Mac Address
2. Multicast Mac Addressing
3. Multicast Mac Address Ipv4
4. Mac Address Multicast Bit

The operation of a switch with respect to multicast packets can be summarized as follows. When processing a packet whose destination MAC address is a multicast address, the switch will forward a copy of the packet into each of the remaining network interfaces that are in the forwarding state in accordance with. The spanning tree algorithm. The high-order 25 bits is the official reserved multicast MAC address range from 0100.5E00.0000 to 0100.5E7F.FFFF (request for Comment 1112). These bits are part of the organizational unit identifiers (OUI). The lower-order 23 bits of the destination IP multicast address are mapped to the lower-order 23 bits of the MAC address. The high-order 4. Multicast MAC addresses are a different animal than unicast MAC addresses, because a unicast MAC address should be unique and have only a single destination interface. Multicast MAC frames may have several destination interfaces, depending upon which devices have requested content from the associated IP multicast stream. Before the Layer 2.

MAC-address consists of 48 bits represented in hexadecimal format. Every 8 bits are separated either by a colon (:) or a hyphen (-). Let’s come up with MAC-address example: 00:26:57:00:1f:02.

Each product, possessing communication interface, has the unique MAC-address. IEEE is the organization that provides manufacturers with source MAC-addresses range to be used in their products: for this, first three octets of a specific value are fixed for each manufacturer. These three octets are called OUI (ORGANIZATIONALLY UNIQUE IDENTIFIER). So, as you already may see, one can easily identify a device manufacturer by its MAC-address. You can do this online by yourself – check for IEEE online database (Be attentive! OUI should be entered with a hyphen!). For the MAC-address given earlier as an example one can define that it belongs to Russian relay protection manufacturer EKRA. The remaining three octets are set by the manufacturer and should never repeat each other in combination with the first three octets of the same value. Since these last three octets identify the network controller of a device, they are usually referred as NIC Specific (Network Interface Card Specific).

Typically, MAC-address of the device can be determined by looking at IED labels – often network interface panel has the label, indicating IED’s MAC-address.

Let’s see what values destination MAC-address can take.

When it comes to transferring data from one device to another, then destination MAC-address field has the value of the recipient – that is, the address which we have discussed above. In this case, destination MAC-address is a unicast (unicast) MAC-address. In substation environment, specifically in IEC 61850 context, destination unicast MAC-address is there in MMS packets.

But what if the same data packet needs to be transmitted to multiple network devices? For this purpose there is a destination multicast (multicast) MAC-address. These MAC-addresses are easily identifiable – least significant bit of the first octet of the destination MAC-address is set to 1, for example, 01-0C-CD-00-00-01. If such a packet is received by Ethernet switch, then the latter forwards it to all other ports – in case no recipient groups are specified at the switch. The possibility of organizing data transfer for the group of devices is one of the differences between using the destination multicast MAC-address and destination broadcast (broadcast) MAC-address. In substation environment, specifically in IEC 61850 context, destination multicast MAC-address is there in GOOSE and Sampled Values messages. For example, one can find a GOOSE with destination MAC-address 01:0C:CD:01:01:21.

Speaking about the destination multicast MAC-addresses it is worth noting another interesting point – IEEE not only assigns MAC-addresses’ bands to device manufacturers, but also to standardization bodies, to uniquely identify the traffic transmitted according to the standards. For this, again, IEEE reserves the values of first three octets. For example, for IEC TC 57 the following three octets are reserved – 01-0C-CD-xx-xx-xx. Then standardization body decides the rules of MAC-address assignment to specific protocols by itself. For GOOSE messages TC 57 WG 10 then determined the fourth octect to be equal to 01 and the range of addresses as: 01-0C-CD-01 -00-00 to 01-0C-CD-01-01-FF; for Sampled Values ​​- the fourth octet equal to 04 and range of addresses as: 01-0C-CD-04 -00-00 to 01-0C-CD-04-01-FF. For example, for PTP and RSTP protocols traffic specific destination MAC-addresses are determined.

Broadcast MAC-address – is always the same: ff: ff: ff: ff: ff: ff. When switch receives such a packet it forwards it to all its ports. Broadcast destination MAC-address is used only by some service protocols such as ARP (Address Resolution Protocol), which we will have a look at next time and which plays an important role in information exchange process in Layer 2 networks.

Summary

1. If you are IED developer and your IED is to have communication interface, make sure IEEE reserves MAC-addresses band for your products. Company will have to pay for this.
2. For protection and control system designers of the future and for the commissioning guys there may be another recommendation – never set the same destination multicast MAC-address for different GOOSE and Sampled Value messages (there are examples of the configuration software not restricting you from doing this). Otherwise, you risk to lose the capability of using multicast filtering function on switches. Keep in mind that there are many IEDs on the market which do not support this multicast filtering functionality. If you are not capable of activating this functionality on the switch then all network devices, including IEDs, will listen to all the messages, even those that they do not really need and this as we have already mentioned, places an impact on GOOSE transfer time. It will increase with the increased loa

A multicast address is a logical identifier for a group of hosts in a computer network that are available to process datagrams or frames intended to be multicast for a designated network service. Multicast addressing can be used in the link layer (layer 2 in the OSI model), such as Ethernet multicast, and at the internet layer (layer 3 for OSI) for Internet Protocol Version 4 (IPv4) or Version 6 (IPv6) multicast.

IPv4[edit]

IPv4 multicast addresses are defined by the most-significant bit pattern of 1110. This originates from the classful network design of the early Internet when this group of addresses was designated as Class D. The CIDR notation for this group is 224.0.0.0/4. The group includes the addresses from 224.0.0.0 to 239.255.255.255. Address assignments from within this range are specified in RFC 5771, an Internet Engineering Task Force (IETF) Best Current Practice document (BCP 51).

The address range is divided into blocks each assigned a specific purpose or behavior.

Local subnetwork

Addresses in the range of 224.0.0.0 to 224.0.0.255 are individually assigned by IANA and designated for multicasting on the local subnetwork only. For example, the Routing Information Protocol (RIPv2) uses 224.0.0.9, Open Shortest Path First (OSPF) uses 224.0.0.5 and 224.0.0.6, and Multicast DNS uses 224.0.0.251. Routers must not forward these messages outside the subnet from which they originate.

Internetwork control block

Addresses in the range 224.0.1.0 to 224.0.1.255 are individually assigned by IANA and designated as the internetwork control block. This block of addresses is used for traffic that must be routed through the public Internet, such as for applications of the Network Time Protocol using 224.0.1.1.

AD-HOC block

Addresses in three separate blocks are not individually assigned by IANA. These addresses are globally routed and are used for applications that don't fit either of the previously described purposes.^[6]

Source-specific multicast

The 232.0.0.0/8 (IPv4) and ff3x::/32 (IPv6) blocks are reserved for use by source-specific multicast.

GLOP

The 233.0.0.0/8 range was originally assigned by RFC2770 as an experimental, public statically-assigned multicast address space for publishers and Internet service providers that wished to source content on the Internet. The allocation method is termed GLOP addressing and provides implementers a block of 255 addresses that is determined by their 16-bit autonomous system number (ASN) allocation. In a nutshell, the middle two octets of this block are formed from assigned ASNs, giving any operator assigned an ASN 256 globally unique multicast group addresses.^[7] The method is not applicable to the newer 32-bit ASNs. RFC3180, superseding RFC2770, envisioned the use of the range for many-to-many multicast applications. Unfortunately, with only 256 multicast addresses available to each autonomous system, GLOP is not adequate for large-scale broadcasters.^{[citation needed]}

Unicast-prefix-based

The 234.0.0.0/8 range is assigned by RFC6034 as a range of global IPv4 multicast address space provided to each organization that has /24 or larger globally routed unicast address space allocated; one multicast address is reserved per /24 of unicast space. A resulting advantage over GLOP is that the unicast-prefix mechanism resembles the unicast-prefix capabilities of IPv6 as defined in RFC3306.

Administratively scoped

The 239.0.0.0/8 range is assigned by RFC 2365 for private use within an organization. Per the RFC, packets destined to administratively scoped IPv4 multicast addresses do not cross administratively defined organizational boundaries, and administratively scoped IPv4 multicast addresses are locally assigned and do not have to be globally unique. The RFC also discusses structuring the 239.0.0.0/8 range to be loosely similar to the scoped IPv6 multicast address range described in RFC1884.

Notable IPv4 multicast addresses[edit]

The following table is a list of notable well-known IPv4 addresses that are reserved for IP multicasting and that are registered with the Internet Assigned Numbers Authority (IANA).^[8]

Ipv6 Multicast Mac Address

IPv6[edit]

Multicast Mac Addressing

Multicast addresses in IPv6 use the prefix ff00::/8. IPv6 multicast addresses can be structured using the old format (RFC 2373) or the new format (RFC 3306, updated by RFC 7371).

The prefix holds the value ff for all multicast addresses.

Currently, 3 of the 4 flag bits in the flags field (ff1) are defined;^[11] the most-significant flag bit is reserved for future use. The other three flags are known as R, P and T.

Similar to a unicast address, the prefix of an IPv6 multicast address specifies its scope, however, the set of possible scopes for a multicast address is different. The 4-bit sc (or scope) field (bits 12 to 15) is used to indicate where the address is valid and unique.

The service is identified in the group ID field. For example, if ff02::101 refers to all Network Time Protocol (NTP) servers on the local network segment, then ff08::101 refers to all NTP servers in an organization's networks. The group ID field may be further divided for special multicast address types.

Notable IPv6 multicast addresses[edit]

The following table is a list notable IPv6 multicast addresses that are registered with IANA.^[17]

Ethernet[edit]

Ethernet frames with a value of 1 in the least-significant bit of the first octet^{[note 3]} of the destination MAC address are treated as multicast frames and are flooded to all points on the network. While frames with ones in all bits of the destination address (FF-FF-FF-FF-FF-FF) are sometimes referred to as broadcasts, Ethernet generally does not distinguish between multicast and broadcast frames. Modern Ethernet controllers filter received packets to reduce CPU load, by looking up the hash of a multicast destination address in a table, initialized by software, which controls whether a multicast packet is dropped or fully received.

Multicast Mac Address Ipv4

The IEEE has allocated the address block 01-80-C2-00-00-00 to 01-80-C2-FF-FF-FF for group addresses for use by standard protocols. Of these, the MAC group addresses in the range of 01-80-C2-00-00-00 to 01-80-C2-00-00-0F are not forwarded by 802.1D-conformant MAC bridges.^[18]

802.11[edit]

802.11 wireless networks use the same MAC addresses for multicast as Ethernet.

See also[edit]

Notes[edit]

1. ^The recommended style for Request for Comments (RFC) documents is 'MSB 0' bit numbering.
2. ^x is a place holder indicating that the value of the flags field is unimportant in the current discussion.
3. ^On Ethernet, the least-significant bit of an octet is the first to be transmitted. A multicast is indicated by the first transmitted bit of the destination address being 1.

Mac Address Multicast Bit

References[edit]

1. ^ ^abcIP Multicast Routing Configuration Guide, Cisco, p. 17-19, retrieved 2017-05-27
2. ^AD-HOC Block 1
3. ^AD-HOC Block 2
4. ^Fall, K.R. and Stevens, W.R. (2011). TCP/IP Illustrated. 1. Addison-Wesley. p. 55. ISBN9780321336316.CS1 maint: multiple names: authors list (link)
5. ^AD-HOC Block 3
6. ^RFC 5771 Section 6.
7. ^'Frequently Asked Questions (FAQ) File for Multicasting'. Multicast Tech. Archived from the original on 2011-05-16.
8. ^'IANA IP multicast addresses assignments'. Internet Assigned Numbers Authority.
9. ^RFC 3376 Section 4.2.14
10. ^RFC 4380 item 2.17
11. ^Hinden, R.; Deering, S. (February 2006) IP Version 6 Addressing Architecture, IETF, RFC4291.
12. ^Silvia Hagen (May 2006). IPv6 Essentials (Second ed.). O'Reilly. ISBN978-0-596-10058-2.
13. ^RFC 3956
14. ^RFC 3306
15. ^RFC 4291
16. ^RFC 2365 section 8.
17. ^'IPv6 Multicast Address Space Registry'. Internet Assigned Numbers Authority.
18. ^IEEE. 'Standard Group MAC Address: A Tutorial Guide'(PDF). IEEE Standards Association. pp. 2–3.
19. ^Patton, Michael A. et. al.. 'Multicast (including Broadcast) Addresses'. cavebear.com. Karl Auerbach.
20. ^RFC 7042 2.1.1.
21. ^RFC 7042 2.3.1.