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Beginner

MAC Filtering on Trunk Port/VLAN

I work at a university and we are using non-cisco controllerless APs in our dorms. The dorm switches are mostly 3750x but we have some old 3560G as well. Here's how an AP port is programmed on both models:

 

interface GigabitEthernet1/0/1

description AP

switchport trunk encapsulation dot1q

switchport trunk native vlan 100

switchport trunk allowed vlan 100,200,300,400

switchport mode trunk

 

We have some problem students who are unplugging the APs in their rooms and jacking their own routers. I am looking for a way to only allow the MAC OUIs of our APs on the Management VLAN (100). We've tried to use port security on the AP port, but we can't seem to target the specific management vlan (100) only and it therefore starts blocking wireless client vlans as well (200,300,400 in this case). We do not have a NAC so that is out of the question, hence why I am looking for something to run on the local switch (or core switch for all dorms). Any help would be greatly appreciated! 

5 REPLIES 5
VIP Advocate

Re: MAC Filtering on Trunk Port/VLAN

Hi, 

I have two ideas to resolve your issue. 

1. Use Dot1x authentication for Wireless AP.

2. I hope VLAN 100 is only for AP management and you can block internet on VLAN 100 use your firewall or router or Switch.

 

Regards,

Deepak Kumar

 

Regards,
Deepak Kumar,
Don't forget to vote and accept the solution If this comment will make help you!
Beginner

Re: MAC Filtering on Trunk Port/VLAN

I've considered 1x auth for the APs, however, I'm not sure how we would set that up for the management VLAN only. Unfortunately, VLAN 100 has to be able to get out to the internet since the APs are cloud managed...

Beginner

Re: MAC Filtering on Trunk Port/VLAN

Hello,

I can propound you this temporary workaround:

because chances are that your student routers are not 802.1q compatible (or you can count on the fact that they won't know how to set this up) the traffic is untagged

My workaround:

  • change the native vlan to an unused vlan (shutdown the vlan) on the trunk link
  • set the AP the same (to send tagged frames for all vlans)
  • disable CDP on the switch port (=do not sent vlan information to your students)
  • Maybe use spanning-tree portfast trunk and bpduguard (unless you do not use STP)
  • [edit] and disable DTP with switchport nonegotiate

This way, all untagged traffic will be dropped and the port will be shutdown if they connect a switch with STP enabled

Regards, Guillaume

 

[edit2]Add more fun:

do not shutdown the native vlan, put a captive portal with a page to ask your students to unplug their devices and plug back the AP

 

Highlighted
Beginner

Re: MAC Filtering on Trunk Port/VLAN

Your workaround is something I've thought of doing, however, would add some steps when installing new units or replacing units (the APs come up by default to not tag management traffic until they receive a config telling them otherwise). The bpduguard wouldn't do us much good for a router which is mainly what is connected when these issues arise. 

 

We are going to try to work some magic with our DHCP server so that it only hands out IPs to certain OUIs. If this doesn't work, we will most likely go to the tagging of management traffic in some way but I was hoping I could avoid that just so the devices stay more plug-and-play. Thanks for the suggestion! 

Beginner

Re: MAC Filtering on Trunk Port/VLAN

Hello,
Like i stated, the workaround i propounded you is a temporary one, and yours looks temporary too: it does not prevents rogue routers to use static addresses.
I voted Deepak post as helpful because i agree that dot1x is the way to go.

 

If you want to add some more magic directly within vlan 100, you could break the ARP with a vlan access-map allowing only your APs to use ARP (and the gateway of course) based on MAC addresses, for example:

10 match ARP traffic from AP and GW MAC adresses=> action forward

20 match ARP traffic from any MAC=> action drop

30 match all (default) => action forward

https://www.cisco.com/c/en/us/support/docs/switches/catalyst-3550-series-switches/64844-mac-acl-block-arp.html
Ps. i restrain my suggestion about portfast and bpduguard, AP in autonomous mode could send bpdu.

Regards, Guillaume

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