Appendix E: Ipsec Nat Traversal; Overview - Cisco RV016 - Small Business - 10/100 VPN Router Administration Manual

IPSec NAT Traversal

Overview

Cisco Small Business RV0xx Series Routers Administration Guide
Network Address Translation (NAT) traversal is a technique developed so that
data protected by IPSec can pass through a NAT. Since IPSec provides integrity
for the entire IP datagram, any changes to the IP addressing will invalidate the
data. To resolve this issue, NAT traversal appends a new IP and UDP header to the
incoming datagram, ensuring that no changes are made to the incoming datagram
stream.
In the following scenario, Router A initiates IKE negotiation, while Router B is the
responder.
RV042
WAN: 192. 1 68.99. 1 1
NAT 2
LAN: 192. 1 68. 1 11. 1
RV042
WAN: 192. 1 68. 1 11. 1 01
NAT 1
LAN: 192. 1 68. 1 1. 1
RV016
WAN: 192. 1 68. 1 1. 1 01
Router A - Initiator
LAN: 192. 1 68. 1 .0/24
192. 1 68. 1 . 1 01
RV016
WAN: 192. 1 68.99.22
Router B - Responder
LAN: 192. 1 68.2.0/24
192. 1 68.2. 1 00
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