500
isakmp
UDP · 0x01F4
Port 500 — isakmp
Networking
Port 500 carries IKE key exchange for IPsec over UDP. Being at or below 1023, only root may open it on Unix.
0–1023. On Unix only root may open one.
Where it sits in 65535
A port number is 16 bits, so it stops at 65535. The narrow band at the left is everything up to 1023.
065535
- Service
- IKE key exchange for IPsec (isakmp)
- Kind
- Networking
- Protocol
- UDP
- Range
- Well-known
- Root needed
- Yes
- Hexadecimal
- 0x01F4
- Binary
- 0000000111110100
- Two bytes
- 1 · 244
Same kind
Running the network itself — handing out addresses, announcing routes, digging tunnels.
Ports next to it
How to read this
- A port number is 16 bits, so it runs 0 to 65535. There is no port 65536.
- Opening anything at or below 1023 needs root on Unix.
- Plain and encrypted often live on different numbers — 80 and 443, for one.
- Numbers like 3000 and 8080 were never registered; those are marked as custom.
Frequently asked questions
Q. What is port 500 used for?
IKE key exchange for IPsec (isakmp) uses it, over UDP.
Q. Does opening port 500 need root?
Yes. It is at or below 1023, so on Unix only root may open it.
Q. Which range does port 500 fall in?
Well-known (0–1023). In hex it is 0x01F4.
Q. Does port 500 have a twin?
Not a separate one. It either was encrypted from the start or negotiates TLS on the same number.