Port 1638 ISMC
Port 1638 is the IANA-assigned ismc port for ISP shared management control (TCP / UDP).
What is port 1638 used for?
Port 1638 is assigned to ismc and uses TCP / UDP. The IANA registry describes the service as “ISP shared management control”. It sits in the registered range, the block used by databases, application servers and developer tooling. Port conflicts here are common when several local services start at once.
Ports are the transport-layer address a service listens on. A client that wants to reach ismc connects to port 1638. A TCP connection is refused when nothing is listening, while a UDP request simply goes unanswered. That is why a port conflict appears whenever two processes try to bind the same number.
Use the commands below to confirm whether port 1638 is actually in use before you change firewall rules. Blocking the port stops new inbound traffic at the firewall, but it does not stop a local process from listening, and it does not remove the service from the machine.
Source: IANA Service Name and Transport Protocol Port Number Registry. Registered assignee: [Nick_Austin].
Check and block port 1638
Copy-ready commands for the protocols assigned to this port. Run the check first, then block only what should not be reachable.
Check on Linux
sudo ss -tlpn 'sport = :1638'
sudo ss -ulpn 'sport = :1638'Check on Windows
Get-NetTCPConnection -LocalPort 1638 -State Listen -ErrorAction SilentlyContinue
Get-NetUDPEndpoint -LocalPort 1638 -ErrorAction SilentlyContinueBlock with UFW
sudo ufw deny 1638/tcp
sudo ufw deny 1638/udpBlock with iptables
sudo iptables -A INPUT -p tcp --dport 1638 -j DROP
sudo iptables -A INPUT -p udp --dport 1638 -j DROPThese commands are examples for a typical host. Check the listener before you change firewall rules, and persist iptables rules with iptables-save or netfilter-persistent. On Windows, use Windows Defender Firewall or New-NetFirewallRule for persistent blocks. The iptables rules here cover IPv4; mirror them with ip6tables if IPv6 is enabled.
Is port 1638 safe to expose?
This port is not on our curated list of services with a widely exploited profile. Exposure is only safe when the listening service is intended, patched and protected by a firewall. Keep the listening service patched and remove it if unused. A default-deny firewall policy with explicit allow rules is still the safest baseline.
Where port 1638 is usually used
Most traffic on port 1638 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.
- Application backends and supporting services that use a fixed registered number.
- Containers or local stacks that publish the port on the host.
- Firewall and exposure reviews before the service goes to production.
Probe the port
Confirm something is listening before you debug the client. This checks a TCP handshake on the port.
nc -vz 127.0.0.1 1638Common problems with port 1638
Connection refused or timed out
Refused usually means the host is reachable but nothing is listening on port 1638. A timeout more often means a firewall drop, a wrong host or a service bound to a different interface.
Port already in use
Find the process holding the port with sudo ss -tlpn 'sport = :1638' or sudo lsof -i :1638. Stop that process or configure it to bind another port; killing it without identifying it can take down a production service.
Firewall rule did not survive a reboot
UFW and Windows Firewall keep rules across restarts. Raw iptables rules do not: save them with iptables-save or the netfilter-persistent package, and re-apply after upgrades that reset the ruleset.
The port is blocked but still reachable
A firewall rule filters inbound traffic; it does not close the listener. Confirm with the check command above and bind the service to 127.0.0.1 when only local clients need it.
Port 1638 at a glance
| Port number | 1638 |
|---|---|
| Service name | ismc |
| Transport protocol | TCP / UDP |
| Category | Application services |
| Range | Registered port (1024–10000) |
| Risk level | Standard/Low |
| Registered assignee | [Nick_Austin] |
| Registry description | ISP shared management control |
| Source | IANA Service Name and Transport Protocol Port Number Registry |
Frequently asked questions
What is port 1638 used for?
Port 1638 (ISMC) uses TCP / UDP. ISP shared management control.
How do I check if port 1638 is open?
On Linux run `sudo ss -tlpn 'sport = :1638'` and `sudo ss -ulpn 'sport = :1638'`. On Windows run `Get-NetTCPConnection -LocalPort 1638 -State Listen -ErrorAction SilentlyContinue` and `Get-NetUDPEndpoint -LocalPort 1638 -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 1638; empty output usually means nothing is bound to it.
How do I block port 1638?
With UFW run `sudo ufw deny 1638/tcp` and `sudo ufw deny 1638/udp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 1638 -j DROP` and `sudo iptables -A INPUT -p udp --dport 1638 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.
Is port 1638 safe to expose?
This port is not on our curated list of services with a widely exploited profile. Exposure is only safe when the listening service is intended, patched and protected by a firewall. Nevertheless, keep the listening service patched and remove it if unused. A default-deny firewall policy with explicit allow rules is still the safest baseline.
Related ports
- Port 1637 · islcISP shared local data control
- Port 1644 · saisehSatellite-data Acquisition System 4
- Port 1636 · isdcISP shared public data control
- Port 1659 · sg-lmSilicon Grail License Manager
- Port 1617 · nimrod-agentNimrod Inter-Agent Communication
- Port 1718 · h323gatediscH.323 Multicast Gatekeeper Discover
Primary data: IANA Service Name and Transport Protocol Port Number Registry.
Last reviewed 2026-10-30 · Methodology · About · Privacy