Packet sequence number checking through a VPN tunnel may be performed by assigning sequence numbers on a per-priority class basis to packets traversing the VPN tunnel. In one implementation, a network device may receive a packet that is to be transmitted over a VPN tunnel, the packet including control information that includes at least a QoS priority class of the packet. The network device may extract the priority class of the packet from the control information and generate a sequence value that describes an arrival sequence of the packet relative to other received packets of the same priority class as the packet. The network device may additionally generate an IPsec header for the packet, the IPsec header including the sequence value and the priority class of the packet; attach the IPsec header to the packet; and transmit the packet through the VPN tunnel.