precursor Posted April 9, 2006 Report Share Posted April 9, 2006 Could anybody explain to me what happens when two ports on the same switch have the same MAC addresses ?Cuz switch transport data with the help of MAC address tables right! Quote Link to comment Share on other sites More sharing options...
homecomputeraid Posted April 14, 2006 Report Share Posted April 14, 2006 Each port on a switch should have a separate MAC Address. Quote Link to comment Share on other sites More sharing options...
precursor Posted April 23, 2006 Author Report Share Posted April 23, 2006 Each port on a switch should have a separate MAC Address.Its working on mine ...with two ports with the same MAC Address. Quote Link to comment Share on other sites More sharing options...
Scarecrow Man Posted April 23, 2006 Report Share Posted April 23, 2006 How many computers are on your network? Quote Link to comment Share on other sites More sharing options...
precursor Posted April 24, 2006 Author Report Share Posted April 24, 2006 How many computers are on your network?three on one switch and 4 on another switch .. the two switches are connected to each other..all the 3 computers have the same MAC addreses while a computer on the other switch has the same MAC address as the computers on other switch(the one where the 3 computers are connected)...and they work fine Quote Link to comment Share on other sites More sharing options...
homecomputeraid Posted April 25, 2006 Report Share Posted April 25, 2006 What you're describing doesn't sound like it should work. Where are you obtaining the information about what MAC address resides where? Quote Link to comment Share on other sites More sharing options...
Lukus Posted April 25, 2006 Report Share Posted April 25, 2006 It would not work. Perhaps your interpreting the wrong information and taking it as a MAC address? Are you getting the MAC address' from the switches or pc's? Quote Link to comment Share on other sites More sharing options...
Scarecrow Man Posted April 25, 2006 Report Share Posted April 25, 2006 Every NIC in the world has a different MAC based on manufacturer, model and other information.It is impossible to have the same MAC on a network card, unless it is a Virtual Machine.http://en.wikipedia.org/wiki/MAC_addressThe original IEEE 802 MAC address, now officially called "MAC-48", comes from the Ethernet specification. Since the original designers of Ethernet had the foresight to use a 48-bit address space, there are potentially 248 or 281,474,976,710,656 possible MAC addresses.All three numbering systems use the same format, and differ only in the length of the identifier. The first three octets (in transmission order) identify the organization which issued the identifier, and are known as the Organizationally Unique Identifier (OUI). The following three (MAC-48 and EUI-48) or five (EUI-64) octets are assigned by that organization in nearly any manner they please, subject to the constraint of uniqueness. The IEEE expects the MAC-48 space to be exhausted no sooner than the year 2100; EUI-64s are not expected to run out in the foreseeable future.MAC addresses that are permanently attached to a product by the manufacturer are known as "burned-in addresses" (BIA) or sometimes as "Universally Administered Addresses" (UAA). The BIA can be overridden with a "Locally Administered Address" (LAA). MAC-48 and EUI-48 addresses are usually shown in hexadecimal format, with each octet separated by a dash or colon. An example of a MAC-48 address would be "00-08-74-4C-7F-1D". If you cross-reference the first three octets with IEEE's OUI assignments, you can see that this MAC address came from Dell Computer Corp. The last three octets represents the serial number assigned to the adapter by the manufacturer. Quote Link to comment Share on other sites More sharing options...
precursor Posted May 3, 2006 Author Report Share Posted May 3, 2006 I know what a MAC address is ....The MAC address can easily be change in Linux boxes using the ifconfig command and many other methods and easier still in windows boxes using this methoddevice manager -> hardware-> property page of the nic-> advanced -> local address -> just type the address in the edit box..and after checking with ipconfig command there its changed.. Quote Link to comment Share on other sites More sharing options...
homecomputeraid Posted May 4, 2006 Report Share Posted May 4, 2006 Why would you want to change it though Precursor, and what havoc can be wrought on a network with multiple devices sharing the same MAC Address? I also reiterate my question about where you're obtaining your information that many devices have the same MAC Address on your network.In a default configuration, MAC Addresses should all be different. On rare occaisons, I've had to program a router to spoof a MAC address on a router to make PPPoE work, but other than that, there's rarely a reason to change them. Quote Link to comment Share on other sites More sharing options...
precursor Posted May 6, 2006 Author Report Share Posted May 6, 2006 ..I know it isn't supposed to work but how is it working..thats what I am questioning..Its got nothing to do with how useful it is .really Quote Link to comment Share on other sites More sharing options...
homecomputeraid Posted May 6, 2006 Report Share Posted May 6, 2006 Did you somehow manually set the MAC Addresses on all of these devices? Quote Link to comment Share on other sites More sharing options...
precursor Posted May 9, 2006 Author Report Share Posted May 9, 2006 Did you somehow manually set the MAC Addresses on all of these devices?yes look at the above post there I have showed how I did it Quote Link to comment Share on other sites More sharing options...
homecomputeraid Posted May 10, 2006 Report Share Posted May 10, 2006 Back to your original question Precursor:Could anybody explain to me what happens when two ports on the same switch have the same MAC addresses ?Cuz switch transport data with the help of MAC address tables right!Why don't you tell us what happens when you put the same MAC Address on several devices? Quote Link to comment Share on other sites More sharing options...
korgg Posted May 18, 2006 Report Share Posted May 18, 2006 here's a scenario. As I understand, there are 2 ports on a switch with the same mac and about 3 or 4 computers with the same MAC... For the switches. They keep their routing table based on MAC address. If two initerfaces have the same address, then they forward packets to those interfaces. I don't see any problem with that. Just more traffic on the network. As for the computers with the same MAC address, also shouldn't be any problem, because they also have IP which are different.So : what happens may be a lower transfer rate between those devices. And sometimes some protocols may fail. It is at least weird, but very educative. :) Please let us know what happens more accurate. Quote Link to comment Share on other sites More sharing options...
homecomputeraid Posted May 18, 2006 Report Share Posted May 18, 2006 I'm not too clear on whether precursor is saying he has several ports on the same switch using the same MAC Addresses, or whether he is saying he has devices off of several ports on the same switch setup with the same MAC Address, but either seems problematic.For communication on a LAN, PC's use Address Resolution Protocol (ARP) to match an IP Address with a MAC Address for local communication. Having numerous machines on a LAN with the same MAC Address but different IP's seems like it would result in very unreliable communication.Here's a sample of an ARP table from a PC:C:\Documents and Settings\tleroy>arp -aInterface: 192.168.1.72 --- 0x2 Internet Address Physical Address Type 192.168.1.1 00-90-7f-1f-5d-0d dynamic 192.168.1.5 00-30-6e-06-e9-15 dynamic 192.168.1.6 00-0b-db-92-15-64 dynamicWhat would happen if both 192.168.1.1 and 192.168.1.5 resolved to the same MAC Address of 00-90-7f-1f-5d-0d instead of having their own unique MAC's? I don't know, but it doesn't look pretty. Quote Link to comment Share on other sites More sharing options...
cozofdeath Posted May 20, 2006 Report Share Posted May 20, 2006 different ips, macs are layer 2 /ips layer3, so ips are routeable macs or layer2 addresses are not. Changing a mac or an ip is very simple and can be used also for different kinds spoofing. Gental mac and smac are good examples. Its usually as simple as a registry edit. Quote Link to comment Share on other sites More sharing options...
homecomputeraid Posted May 31, 2006 Report Share Posted May 31, 2006 There isn't much purpose in doing this for most home users. The only exception I know of that would help a home user resolve a problem is if they have PPPoE from their ISP and want to spoof the MAC address of their PC with their Router on the WAN port to get a connection. I'm not saying it's impossible, or even difficult, I'm saying it could cause problems unless you know what you're doing, or are willing to learn, and isn't something most home users should do. It sounds from Precursors questions like he was expiramenting and probably could answer his own question before long. Quote Link to comment Share on other sites More sharing options...
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