UDP port 500 is the ISAKMP port for establishing PHASE 1 of IPSEC tunnnel. VPN-GW1-----nat rtr-----natrtr-----VPNGW2. If two vpn routers are behind a nat device or either one of them, then you will need to do NAT traversal which uses port 4500 to successfully establish the complete IPEC tunnel over NAT devices.

2021年12月28日 · In other words, RTR-Site1 encapsulates ESP packets inside UDP/4500 for Source and Destination Ports. After this encapsulation, now NAT device can translate the ESP packets. It will change the source port from 4500 to a random port and the source IP address from 172.16.1.1 to 100.1.1.1, and kept the destination port 4500

2023年2月1日 · In other words, RTR-Site1 encapsulates ESP packets inside UDP/4500 for Source and Destination Ports. After this encapsulation, NAT device can now translate the ESP packets. It will change the source port from 4500 to a random port and the source IP address from 172.16.1.1 to 100.1.1.1 and kept the destination port 4500

2011年5月23日 · This UDP port 4500 is used to PAT ESP packet over ipsec unaware NAT device. if this UDP encapsulation in not done then the ESP packet will be dropped and data will not flow. well my question is : the ESP packet starts after 9 th packet of quick mode. but the NAT-T is detected and changes the port from udp 500 to 4500 on 5th packet. why is this ...

2021年9月1日 · Also enabling Nat-Traversal on the gateways resolves the problem with the authenticity and integrity checks as well, as they are now aware of these changes.During phase 1, if NAT Traversal is used, one or both peer's identify to each other that they are using NAT Traversal, then the IKE negotiations switch to using UDP port 4500.

2011年4月17日 · And since ESP protocol can't be NATed as it is not a TCP or UDP port, but a protocol, you can enable the VPN peer with NAT-T (NAT-Transparency) which by default run on UDP/4500. It encapsulates the ESP procotol into UDP/4500 so it can be NATed if it's required. In this case, the IPSec VPN protocol is: - UDP/500 (Phase 1) - UDP/4500 (Phase 2)

2010年10月27日 · Devices exchange two NAT-D packets, one with source IP and port, and another with destination IP and port. So the receiving device recalculates the hash and compares it with the existing, if they don't match a NAT device exists. NAT-T encapsulate IPSec packets in UDP packets with port 4500, providing information to PAT device for translation.

2022年12月29日 · Thank you for the response. But what if now there is a parameter and an internal firewall. There is already an existing tunnel on the parameter firewall, and will need to port forward 4500 and 500 to the external IP of the parameter firewall to the internal firewall's WAN IP, will that interrupt the parameter firewalls tunnel?

2009年1月5日 · Hello, I have a site to site vpn between two Cisco 2811 routers passing through a PIX 515 on the core side and an ASA5510 on the remote side. Although I have ports ESP and ISAKMP open the tunnel also requires udp port 4500. Is that normal? If not any ideas how it can be fixed? Thanks.

In that case, the two ends start their negotiation to set up the vpn tunnel by using ISAKMP udp port 500, and as soon as a natting/patting device is detected along the path the two ends will switch to port udp 4500 and start encapsulating the esp packets into udp, so basically udp port 500 was used for ISAKMP negotiation only instead udp port ...