11 Chapter 11. Network Address Translation traversal support This chapter discusses the support for an IP Security (IPSec) tunnel that traverses a Network Address Translation (NAT) or Network Address Port Translation (NAPT) device. We provide a high-level overview of NAT and NAPT, explain why NAT and NAPT pose problems for IPSec, and describe the support for IPSec tunnels that traverse a NAT or NAPT