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Are ports between 1-19 still used for anything?
elwebmaster
Member
in General
I looked up the Wikipedia page and while these ports appear to have been relevant in the past, I wonder are they still used? Would you expect to have services listen on ports between 1 and 19 ? I want to reserve these ports and I am hoping they will never be needed by people on VMs.
Comments
1 TCP UDP TCP Port Service Multiplexer (TCPMUX)
2 TCP UDP CompressNET[1] Management Utility[2]
3 TCP UDP CompressNET[1] Compression Process[3]
4 TCP UDP Mesh Connection Protocol
5 TCP UDP Remote Job Entry
7 TCP UDP Echo
9 TCP UDP Discard
11 TCP UDP Informations about the systat-Service
13 TCP UDP Daytime (RFC 867)
15 TCP UDP netstat Service[4] (unoffical)
17 TCP UDP Quote of the Day (QOTD) –
18 TCP UDP Message Send Protocol
19 TCP UDP Character Generator Protocol (CHARGEN)
Thanks, but are they actually used in practice on servers?
Generally not.
OP wasn't asking about RFC allocation ;-).
@elwebmaster no, they aren't used often theee days.
Why do you need these specific ports @elwebmaster ?
I have a feeling this is some hokey "vps #1 corresponds to port #1" thing...
There are TONS of ports that are not in use...let's see, 0-65535, how many are officially assigned:
# grep -v "^#" /etc/services | grep -v "^$" | awk '{ print $2 } ' | awk -F\/ '{ print $1 }' | sort -u | wc -l 341So, > 60,000 available ports for you to use...and you want to take one already in use?
Go look in /etc/services and find some ports you like and leave the official ones alone.
BONUS: you can use ones > 1024 without being root!
> # grep -v "^#" /etc/services | grep -v "^$" | awk '{ print $2 } ' | awk -F\/ '{ print $1 }' | sort -u | wc -l > 341 >Every VM will have a private IP. Services will be listening on these 19 ports. A public IP will be forwarded to ports > 19. Clients can run their services on any port > 19 as long as they make them listen on all interfaces. At any point clients can "duplicate" the VM. A new VM will be created from snapshot with its IP set to a new private IP and a new public IP forwarded to it. The infrastructure services on ports 1-19 will immediately be accessible to the infrastructure but not on the public IP.
I was originally planning to do it with two IPs per VM but it makes it hard to clone the VM if the IP services are bound to changes.
Qotd? Really?!
Yep: https://en.wikipedia.org/wiki/QOTD
And many providers block it...e.g., Vultr:
"Port X seems to be blocked on my VPS, are you blocking it?
We block several ports that are commonly abused for DDOS attacks. This includes TCP and UDP ports 17, 19, 1900. These blocks are permanent, and cannot be removed. "
Useful trivia. Not a lot of people know that...