Unfortunately, this is not an uncommon occurrence. Fortunately, the Foundry FES2402 switches that we are using at these remote sites gives the network admin(s) some tools to help prevent users from connecting unauthorized devices to our networks.
The first tool is a simple MAC filter. In this case, there is a fixed number of devices that are supposed to be connected to our network, the MAC addresses of these devices are known, and therefore, we can create a filter to allow only these MAC addresses on a given port(s). Alternatively, if there is a known MAC address (or multiple addresses) that we *don't* want connected to a given port, we can create a filter to disallow it (or them). Here's how you do it:
conf t
mac filter 1 deny 0015.c507.ae6b ffff.ffff.ffff any
mac filter 128 permit any any
interface ethernet 7
mac filter-group 1 128
mac filter-group log-enable
This filter denies access from MAC address 0015.c507.ae6b to eth7, but allows access from all other MAC addresses.
Keep in mind that there are a few tips and a couple of "gotchas" in the simple MAC filter. First, just as when creating an Access Control List (ACL) or firewall rule for an IP address, you can filter for a portion of the MAC address, if you like:
conf t
mac filter 1 deny 0015.c507.ae6b ffff.0000.0000 any
mac filter 128 permit any any
interface ethernet 7
mac filter-group 1 128
mac filter-group log-enable
This will only match the "0015" portion of the given MAC address.
For a "gotcha," while there are many interface parameters that you can set using a range of Ethernet ports on a Foundry/Brocade switch, this isn’t one of them. For example, this…:
conf t
int eth 1 to 24
mac filter-group 1 128
mac filter-group log-enable
…doesn’t work. You can only apply a filter to a single interface at a time.
Another "gotcha" is that if you create multiple filters, then when applying the filters to an interface, you MUST include all of the filter groups on one line. If you try to put the filter groups on multiple lines, you will only get the LAST filter:
conf t
mac filter 1 deny 0015.c507.ae6b ffff.ffff.ffff any
mac filter 128 permit any any
int eth 7
mac filter-group 1
mac filter-group 128
mac filter-group log-enable
This will result in ONLY filter 128 ("permit any any") being applied to the interface -- NOT AT ALL what you (presumably) intended.
The second tool is a lock that allows the admin to limit the number of devices that can access a given port on the switch. Unfortunately, this only sends an SNMP trap for a violation -- it does not actually disable the port or drop traffic from an unauthorized MAC address. Here's how you do it:
conf t
lock ethernet 15 addr-count 1
This applies a "lock" to allow only a single MAC address to eth 15 on a FES2402 switch. However, this isn't a terribly useful tool, as it only notifies the admin when someone attempts to attach an unauthorized device.
However, there is a third tool that takes the "lock" concept and gives it some teeth, so to speak. This is the MAC Port Security feature, and it can be applied either globally or directly to an Ethernet interface. Here is how you apply the MAC Port Security feature to a specific interface:
conf t
int eth 0/1/15
port security
enable
maximum 1
age 5
violation restrict
In this example, we applied Port Security to Ethernet 0/1/15, enabled port security, set a maximum of 1 authorized IP address to this port, set the aging timer to drop the authorized IP address after 5 minutes (that is, if five minutes elapse without receiving a frame from a device, it will clear the MAC address entries for the interface, allowing a new device to connect), and telling the port to drop frames from any unrecognized device. You can set up to a maximum of 64 known MAC addresses per port. The aging timer can be set from zero (never time out a recognized MAC address) to 1440 minutes. The admin can choose between "restrict" and "shutdown" when a violation occurs; restrict will simply drop frames from an unknown device, whereas shutdown will disable the Ethernet interface for a specified period. If you choose "shutdown", then the next parameter is a number between 0 and 1440, where zero means shut down the port permanently, and any other number is the time to shut down the port, in minutes.
In addtion, you can manually specify allowed MAC addresses on the port, or you can configure to automatically discover and save allowed MAC addresses to the startup configuration. To manually specify an allowed MAC address:
conf t
int eth 0/1/15
port security
enable
secure 0123.4567.89ab
This configuration manually specifies that only the device with the MAC address "0123.4567.89ab" should be allowed to access the port.
Alternatively, to have the Foundry auto-discover an allowed device, then write the MAC address to the startup configuration:
conf t
int eth 0/1/15
port security
enable
autosave 60
This will automatically detect the MAC address of the device connected to the port and write its MAC address to the startup configuration every 60 minutes. Only that device will be allowed to connect from then on.
