In article , Rainer Birkenmaier wrote: :this may sound like a strange thing but it does make sense in my case:
:Context: :I want 2 machines to receive the same ethernet packages (for redundancy :reasons). The communication is unidirectional and uses UDP on top. :Currently this works by having 2 nodes with the same HW-/Ethernet-address :and IP-address on one hub(!)
There are probably other ways to achieve the redundancy, but I lack the experience in that area. Depending on what has to be accomplished in your situation, you might find the material on Vincent C. Jone's web site to be useful.
:Question: :How can I do the same thing with a switch? :Originally I thought this wasn't possible, then I found out about port :mirroring which kinda-works (but won't scale). Later on, somebody :told me that this (having the same HW-address on 2 switch-ports) is :supposed to work out of the box with ANY switch. Can anybody help me on :this last statement?
It's obviously false. Many switches do not allow you to assign particular MAC addresses to ports. The MAC address of a particular port isn't even necessarily allocated by a fixed algorithm -- it could be dependant on the order the ports came up. Static MAC allocation for layer 2 ports seem to be quite common, though.
Something I read awhile ago indicated that each layer 2 port is required to have distinct MAC addresses in order for spanning tree to work properly. I have not investigated this point to determine whether there are allowed exceptions beyond turning off spanning tree for those ports.
:Of course I tried that and it wouldn't work, it just :sent data the the port that last received the answer to an ARP. :Any hints?
Oddly enough, just a couple of hours ago, I happened upon something that would perhaps suit your needs. I was reading through the release notes on the Cisco 3750 series, for IOS 12.1(14)EA or so [might have been 12.2(14)SE] and saw a "caveat" described there. It seems in that particular software release, if you had assigned a static MAC address to a port with active port security, then packets destined for that MAC were flooded to every port in the VLAN. {I'm probably missing out on a detail or two of what was required to cause the situation.} The implication is that 1) the Cisco 3750 allows user-specified MAC addresses on ports; and 2) you might be able to turn the flooding bug to your advantage in your situation. You could probably find the bug description by googling cisco.com for
3750 release-notes flooded
There may be other methods of achieving the desired end. Most modern switches allow per-vlan spanning tree and per-vlan MAC address tables so as to handle situations in which the same MAC address might show up on different ports of a switch due to participation in different VLANs or due to redundant links. Possibly HSRP would be suitable for your needs.
Sorry for the vagueness: I've only had -useful- modern multilayer switch for a couple of weeks and there is a lot to learn on it.