I work in  an ISP multiple times i have encounter that other ISPs wants to run his customer through my network and they share the VLAN ID that i can't allow for them because it has been used by my network. i want to ask if there is any possibility to...

An NTP servere confugured on VM. i have multiple switches in  my network i.e 3550,3560,3750,4948. I configured NTP server on all these switches to sycnchronize the time. works perfectly. but unfortunately its stops synchronization on some of switches...