![]() ![]() Then you chop it into 8 bit chunks and turn it back into decimal. ![]() If I happened to own ASN 5660, I could convert my ASN to a 16 bit number. The range can/should be used on an experimental basis by anyone that owns a registered ASN. What does GLOP stand for? I don’t think anyone actually knows to be honest. This range is referred to as GLOP addressing. We’ll touch on SSM later but for now we should just know that SSM is means for a host to indicate that it would only like to receive packets from a specific source. This range is used for source specific multicast (SSM). That is, multicast routers will forward packets with a destination IP in this range. ![]() This range is used for network protocols that ARE forwarded. This range is also considered to be part of the permanent IANA allocation. Multicast routers do NOT forward packets with a destination in this range. This range is used for network protocols on a local segment. This range is considered to be part of the permanent IANA allocation. The entire layer 3 multicast range (224.0.0.0 through 239.255.255.255) is split into a few different allocations. Like unicast and broadcast traffic, multicast has a predetermined set of layer 2 and layer 3 addresses. Now that we have a firm hold on how unicast and broadcast handle layer 2 and layer 3 addressing, let’s talk about how multicast does so (I know I haven’t actually explained what multicast is yet, just keep with for a few more paragraphs!). Ok, I know I was kind of beating the dead horse on that, but these are important concepts to know before you start dealing with multicast since the exact same principles apply. If the layer 3 broadcast didn’t use the layer 2 broadcast destination, it wouldn’t work at all. The NIC on my computer is currently only listening to frames destined to two addresses. The MAC address of the packet HAS to be the layer 2 broadcast. The layer 3 destination is also what we expected since we were directly pinging the 10.20.30.255 address, but note how the layer 2 destination also turned into the layer 2 broadcast destination of ff:ff:ff:ff:ff:ff. The source layer 2 and layer 3 is as we expect (the host sending the broadcast). Note what happens when we send a layer 3 broadcast packet. I generated this traffic by sending an ICMP echo request to the broadcast address of the network (10.20.30.255). ![]() The layer 2 unicast addresses are show in the red boxes and you can see that the source matches the PC BIA that I listed above. The layer 3 unicast addresses are shown in green boxes. This shows a ICMP echo reply packet sent from my PC (10.20.30.41) to another host on my network (10.20.30.40). Taking a look at a sample of unicast traffic, we can see that these rules hold true… Packets sent to that IP address should be processed by all devices on that layer 3 segment. For instance, on my home network the broadcast IP for my computer would be 10.20.30.255. Note that when I say usable, I’m referring to it as “it has a purpose” not useable in the sense of end host addressing. The broadcast address for layer 3 is the last ‘useable’ IP address in the network. The subnet mask is crucial in defining the layer 3 broadcast address. Note that I list not only the actual IP address, but I also include the subnet mask. Another layer 3 device sending me direct unicast traffic would send it directly to that IP address. All devices on that segment will listen to not only their local BIA, but also this broadcast address and process frames destined to either.įrom a layer 3 perspective, a unicast address is an IP address (we’ll deal with IPv4 only during this post). FF:FF:FF:FF:FF:FF is known as the broadcast MAC address. If I wish to broadcast traffic on a layer 2 segment, I would send a frame with a source of my MAC address and a destination of FF:FF:FF:FF:FF:FF. For instance, my home computers BIA is 10:BF:48:88:3E:92. If a device wishes to send data to a specific device on a layer 2 segment it would send it to the PC’s BIA. Layer 2 BIAs (MAC addresses) should be unique across the entire global network. Both of those technologies can be represented in both the layer 2 as well as the layer 3 layers.įrom a layer 2 perspective, a unicast address is the BIA (Burned In Address) of the actual NIC unless its manually changed. We know what unicast traffic and broadcast traffic are. Layer 2 and Layer 3 Unicast/Broadcast addressing We’ve covered IP multicast many times in previous posts, but until now, we’ve never really talked about what it is and how it works. ![]()
0 Comments
Leave a Reply.AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |