On Friday, 10/30/2009 at 11:46 EDT, "van Sleeuwen, Berry" <[email protected]> wrote: > Hello Marcy, > > Indeed we have two VM systems and we once had a MAC prefix. But the > prefix had been removed some time ago (actually by accident but it had > not been setup again since then). > > I was told that duplicate MAC addresses would not be a problem in a > TCPIP connection. Only when for instance a CCL is running there could be > a problem with duplicate MAC's on SNA connections as we had discovered a > few years ago. > > Since we have been running with duplicate MAC addresses for quite some > time I would expect this not to be a problem that hits us only last > Friday. I would expect that we either would have had problems with this > for the last 3 years or not at all. Up untill now I would say the latter > is the case. > > So the question would be if in IP connections, is it realy a problem to > have duplicate MAC addresses?
That depends on how the MAC address is being used. Technically, the MAC is only required to be unique within a single layer 2 broadcast domain (e.g. VLAN), but applications can touch the MAC address and use it ways that change the rules. DHCP, for example, can be configured to hand out IP addresses based on MAC address. If the DHCP daemon doesn't allow you to segregate definitions based on the the interface, then the MAC must be 'globally' unique (for various values of 'globally'). As a general rule, unless you have a specific reason to have adapters on your network with the same MAC address, it is best to have unique MACs. It's what the rest of the world has come to expect. Alan Altmark z/VM Development IBM Endicott ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
