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323

The MAC address might be unique, but there's nothing special about the number that would indicate where it is. MAC 00-00-00-00-00-00 might be on the other side of the planet from 00-00-00-00-00-01. IP is an arbitrary numbering scheme imposed in a hierarchical fashion on a group of computers to logically distinguish them as a group (that's what a subnet is). ...


69

Because the routing tables would become impossibly large. IP addresses are allocated hierarchically, so a router can group routes by address prefixes. The number of autonomous systems present on the net now is reasonable enough to fit in today's hardware. On the other hand, the distribition of MAC addresses across the network is random and completely ...


45

There are actually 4 sets of Locally Administered Address Ranges that can be used on your network without fear of conflict, assuming no one else has assigned these on your network: x2-xx-xx-xx-xx-xx x6-xx-xx-xx-xx-xx xA-xx-xx-xx-xx-xx xE-xx-xx-xx-xx-xx Replacing x with any hex value.


34

The world doesn't run exclusively on ethernet(at least historically). The IP layer is independant of the hardware layer beneath it. PPP nodes don't have Mac addresses. Neither do arcnet, token ring, fddi, hppi. Those other standards may not be as relevent today, but ethernet may be replaced with other technologies in the future and it would be transparent ...


29

Further to the hierarchical routing of IP, having them separate from MAC addresses allows you to change your network card or whole computer while retaining the same IP address (and thus logical network topology). This abstraction allows for much more flexible and maintainable networking.


28

The first half (24 bits) of your mac-address is called an OUI (Organizationally Unique Identifier), and identifies the company. The list is available on ieee.org: http://standards.ieee.org/develop/regauth/oui/oui.txt They are formatted like this: 00-03-93 (hex) Apple Computer, Inc. 000393 (base 16) Apple Computer, Inc. ...


24

I use macaddr=$(echo $FQDN|md5sum|sed 's/^\(..\)\(..\)\(..\)\(..\)\(..\).*$/02:\1:\2:\3:\4:\5/') The benefit of this method, over a completely random number, is that it's possible to reliably reproduce the MAC address based on the FQDN of the machine, which I find useful sometimes. The 02 for the first octet just sets the "locally assigned" bit, which ...


22

Take a look at the OSI model: http://en.wikipedia.org/wiki/OSI_model This explains why it doesn't make sense to make routing, a layer 3 concept, decisions based on a physical, layer 2, mechanism. Modern networking is broken into many different layers to accomplish your end to end communication. Your network card (what is addressed by the mac address ...


18

Well, this depends on what kind of switch you are using. The very basic types operate at the link layer and are not aware of IP addresses. They use MAC addresses for their operation. These switches are often unmanaged. However, there are also more intelligent switches, which offer functionality at the IP layer, such as access control lists, and these are ...


18

As @Bart De Vos says the IEEE maintains the canonical list of OUIs. Additionally there is an Individual Address Block (IAB) list at http://standards.ieee.org/develop/regauth/iab/iab.txt. However, entries can be privately registered which means that they will be omitted from oui.txt and iab.txt. The Wireshark development team maintains a much more complete ...


17

Just remove /etc/udev/rules.d/70-persistent-net.rules then restart. And all will be fine.


15

A MAC address conflict is what's happening. Since you have two objects with the same MAC address, packets bound for either device will end up at one or the other, and where you "intend" for them to go doesn't matter a whole lot. Don't assign the same MAC address to your "COMP" as you have for your VMWare server. MAC addresses should be unique, when you ...


14

I had to "fix" the same situation in one of our production plants about 6 years ago. I got to tell the production engineers that they were idiots :-). In their defense: This was the first networking product ever and R&D hadn't exactly thought the production ramifications through. There was no way around it then (and still isn't now). Each device ...


12

Source MAC = A Destination MAC = C Why: When A needs to send data to another host it first determines whether or not the detination host is on the local network. Upon determining that the destination is not local, A sends the data to it's configured default gateway, which is C. Why not B? Because switches (bridges) when operating at layer 2 don't modify ...


11

When online I use MAC_Find: - it's helpful if you're only looking up one or two. If you're wanting to look up a larger amount or a list of MAC addresses it will be easier to run a script to grab the line (using grep or something similar) from IEEE's OUI List. Note that the oui.txt file seperates the MAC address by dashes rather than colons. To make life a ...


11

On Mac OS X : ifconfig <interface> ether <new mac address> On linux : ifconfig <interface> hw ether <new mac address> On Win XP : http://devices.natetrue.com/macshift/


11

You can use macvlan to create multiple virtual interfaces with different MAC addresses. ip link add link eth0 address 00:11:11:11:11:11 eth0.1 type macvlan ip link add link eth0 address 00:22:22:22:22:22 eth0.2 type macvlan In theory that should be all you need, though at some point something broke in the kernel and it would cause it to use one MAC for ...


11

To address your most recent content update, if you want to "pass" the physical NIC through to the guest. This article describes it for ESXi 4 and this article walks you through it for ESXi 5. You use DirectPath I/O to present the physical NIC directly to the guest. When you do this, the host will not use that NIC at all. The way you're trying to do it now ...


11

You're an idiot, don't connect things with the same MAC to the same network. ;-) Seriously, a MAC address is absolutely fundamental to the way that the IEEE 802.3 networks work. With multiple devices on the same physical bit of Ethernet cable with the same MAC, each receiver will respond with a "that's me" when an ARP packet flies by. So, you have to ...


10

why not just try: getmac /v KISS Principal at play!


10

Generally speaking, "promiscuous mode" means that a network interface card will pass all frames received up to the operating system for processing, versus the traditional mode of operation wherein only frames destined for the NIC's MAC address or a broadcast address will be passed up to the OS. Generally, promiscuous mode is used to "sniff" all traffic on ...


10

If your NICs have the same MAC addresses, you should stop fiddling around with workarounds and return them to the manufacturer as defective. Get proper replacements and continue on as normal. Incur the downtime once instead of the recurring issues that will pop up from continuing to hack together a "solution."


10

You don't prevent MAC spoofing, since it's entirely client-side. This is the reason that no one that really cares about security is using MAC whitelisting or blacklisting. If you care about controlling what devices connect to your network, you should be using 802.1x with device certificates issued by your own internal CA that you control, or with some form ...


10

When a switch has the ability to learn what MAC addresses each of its ports serves, then uses that to determine which port to send ethernet packets out, what is that feature called? That's called. Wait for it...switching. All switches do that, and it's a key differentiator between hubs and switches. Also, does every switch with that feature also ...


9

Something like this: class "specialK" { match if substring (hardware, 1, 3) = 00:01:02; } subnet 10.0.0.0 netmask 255.255.255.0 { pool { range 10.0.0.16 10.0.0.32; allow members of "specialK"; } } hmm, is it supposed to be (hardware, 0, 2) or (.. 1, 3), test it out. :)


8

You will have to access the information available on your managed switches. If you have an unmanaged network, I don't see a way to do that. This is assuming the target computers are capable of Wake-on-LAN (WoL). In this case, a link to the server is established (look for the flashy link LED), and the network card is listening to WoL broadcasts. AFAIK, the ...


8

There's always more than one way to do anything :) Solution 1 Motherboards with one of each? Blacklist whichever module (ethtool -i eth0) is supporting the Realtek card. Ubuntu supports module_name.blacklist=yes to blacklist it at boot and you should be able to change the modprobe options in the preseed environment so that it doesn't get probed later. ...


8

b0fh is right - but also because MAC addresses are not always unique. See for example in virtualization scenarios. Here multiple hosts can serve virtual machines with the same MAC addresses.


8

It's possible for two hosts to have the same MAC, due to spoofing, a mistake during manufacturing, or willful negligence on the part of the manufacturer. So, 1) In general, an Ethernet switch keeps a table of which MAC addresses are attached to which ports. It bases this table on the source address of frames it receives during the normal operation of the ...


8

"You're an idiot, don't connect things with the same MAC to the same network" (you said that'd be ok) :) The correct answer to your problem is to fix the manufacturing process to assign different MAC addresses on the devices, either sequentially or however (date mfg'd then a unique #, etc.)



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