How unique are mac addresses generated by VLANs?

[aehchua]

I gave a take home exam using packet tracer.  A number of students made exactly the same mistake and all of them have the same MAC addresses in the VLAN beginning with 0001.43a4.8401.  There's a difference between SUSPECTING cheating and PROVING cheating.  Is this conclusive or does packet tracer recycle the same MAC addresses?

[balaji.bandi]

every vendor has pre-defined mac address allocated. each program has build in MAC address database when you create vlan that MAC address from that database (this can also be change manually, if you like to do so)

[aehchua]

Sorry. Doesn't answer my question. I am talking about Packet Tracer. This is training simulation software made by CISCO. Packet tracer generates false MAC addresses when we define VLANs on the simulated layer 3 switch. I have observed this is at least semi-random generated. But how random is it? If I see two students with the exact same set of MAC addresses in one exercise, can I conclude they are cheating? Note Packet Tracer seems to start at a specific MAC address and then auto-numbers from there. The starting MAC address has some randomness- I have students beginning with different MAC addresses.

[balaji.bandi]

 I am talking about Packet Tracer. This is training simulation software made by CISCO. Packet tracer generates false MAC addresses when we define VLANs on the simulated layer 3 switch. I have observed this is at least semi-random generated

yes i was referring same, depends on how the simulator developped and added MAC address list to start and end, it keep track thatMAC address like every program does.

Sure if the simulator are different same program used, so MAC address will be same.

Not sure you can change that manually any range (not sure)

But i use other simulators Like PNET / EVE - we can define what MAC address range to be, since that MAC address reside locally.

[aehchua]

So does packet tracer generate random MAC addresses or draw from a limited pool?

I have 50 students. I am looking at their scripts. Most have distinct MAC addresses, and some don’t. Is this packet tracer, or cheating?

I’ll run some stats on the distribution and report if no one can answer.

Sorry, but I am having difficulty parsing what you are saying.

[balaji.bandi]

yes correct the MAC address and binded to the device based on the Logic cisco used to create this program. that is fixed (I am not aware any multi-user available)

if you looking random MAc address (since PT is Limited - as per I know)

I would suggest other platforms which give more options for training institutes.

cisco CML - Multi-user - Paid to check the price on cisco side.

PNET Lab - Free - Web GUI based ( you can have many users, make sure you have a good compute server available)

eve-ng - training version available check on their side.

[MHM Cisco World]

next time 

make each student use specific port and if you have alot then make each group use specific router. 

BTW 
I try run same platform twice, each time it give me different mac

[aehchua]

They each are using a personal instance of packet tracer. I don't run a server.

[MHM Cisco World]

even so, when you ask Q just specify the port must be use for each one or specify router for each group.  

[aehchua]

Do not understand specify port. The question has students set up a network with a layer 3 switch and a bunch of layer 2s. The ports used on the layer 3 are specified- gig 1/1/1 to 1/1/3 are fiber gig and 1/0/1 to 1/0/5 are copper gig. The topology is given to students.

Students have to do vlan setups to departments and a Wi-Fi WLC/LAP setup and then map vlans to switches, interfaces and dhcp. Each layer 2 is either a pure trunk switch or a switch for two or three departments (multiple access nodes on the switch with a possible trunk to the LAP and a trunk to another switch). Each department has its own VLAN.

There’s a router, but it is mainly acting as a gateway to the outside world and is the subject of the next exam. There’s not dot1q on the router.

How would forcing use of specific ports help me identify people who copy?

[aehchua]

Okay, I have concluded to MY satisfaction that they are unique.  I ran stats on 50 students in my class and I found every MAC address series was unique except:

0001.43a4.8401 (16 students)
0009.7c23.b301 (4 students)
0001.c7e6.ee01 (2 students)

who are now being referred for disciplinary action.  Sadly, I've caught these students doing the same thing in my previous unrelated classes.

[MHM Cisco World]

let assume that PKT give same MAC for same port for same router each time you run PKT for first time 
how we can get rid of this case 
we ask students to use different port in that case 100% we sure that MAC address never be same. 
that my idea 

[aehchua]

I have satisfied myself that PKT generates random MAC. Students are admitting to cheating and asking for another chance. I can see the merits of what you are saying, but the logistics of marking an assignment like you envision is difficult. I have to cross-index student to port. I have to mark 50 students. A one minute increase in marking translates to 50 more minutes marking.

[MHM Cisco World]

Yes I get your point.