The hub uses UDP 500 and UDP 4500 to talk back to all the spokes, except for the Cisco 1100 IOS-XE were it uses UDP 512 to reply to ISAKMP messages. UDP 512 seems to be a …

SonicWall IKE VPN negotiations, UDP Ports and NAT UDP port 500 is used for IKE all the way through . When there is no NAT between the two peers (both peers have public IP addresses on their WANs) or. When there is a NAT between the two peers, but one or both sides doesn’t support the official NAT-Traversal standard . UDP port 4500 is used for IKE and then for encapsulating ESP data Port 500 (tcp/udp) :: SpeedGuide Xbox One (LIVE) ports: 3074 TCP/UDP, 53 TCP/UDP, 80 TCP, 88 UDP, 500 UDP, 3544 UDP, 4500 UDP isakmp_sub_print in tcpdump 3.6 through 3.7.1 allows remote attackers to cause a denial of service (CPU consumption) via a certain malformed ISAKMP packet to UDP port 500, which causes tcpdump to enter an infinite loop. References: [CVE-2003-0108]

TCP / UDP: UDP; Delivery: No; Protocol / Name: isakmp; Port Description: isakmp. Used in FW-1 VPN for key exchange & synch when using ISAKMP or IPSEC crypto between FW-1’s. FW-1 Ports: tcp 256, tcp/udp 259, udp 500, tcp 900. Virus / Trojan: No Tip! Use our free Digital Footprint and Firewall Test to help verify you are not infected.

Verify ISAKMP parameters match exactly. Verify pre-shared-keys match exactly. Check that each side has a route to the peer address that you are trying to form a tunnel with. Verify ISAKMP is enabled on the outside interfaces. Is ESP traffic permitted in through the outside interface? Is UDP … Testing ISAKMP with netcat – Network Notes May 20, 2016

Confirm the presence of the isakmp sa using the show crypto isakmp sa command. This identifies which peer initiated the connection, and also how the connection was authenticated. The Private IP address is the VPN “inner address” assigned by the controller from the VPN address pool.

What is NAT-Traversal (Network Address Translation The TCP and UDP Port Numbers are not visible for a NAT device performing PAT between IPSec Peers, because TCP/UDP headers are encrypted and encapsulated with ESP header. When IPSec is used to secure IPv4 traffic, original TCP/UDP Port Numbers are kept encrypted and encapsulated using ESP. Following image shows how IPSec encapsulates IPv4 datagram. InfoSec Handlers Diary Blog Nov 01, 2009