[CentOS] Run commands automatically when bringing up/down network interfaces?

I'm looking for a capability similar to Debian/Ubuntu's pre/post up/down network commands capability.

The problem: we've got a colo in which hosts talk directly to the hosting provider's router (through a bridging firewall) and hence our hosts MAC addresses are cached by the router.

We should be able to solve this by pinging the router directly when bringing up the interface, rather than waiting (a day) for the router's ARP cache to expire.

Yes, this means we're switching which hosts respond to a specific IP address, yes, we have to do this periodically.

An alternative would be to remap the MAC address, though pinging the router seems cleaner, and the MAC remap would /still/ have to run when the interface is brought up/down.