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Port 748 (ris-cm)

IANA assigns port 748 to ris-cm: Russell Info Sci Calendar Manager.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
ris-cm TCP Russell Info Sci Calendar Manager - -
ris-cm UDP Russell Info Sci Calendar Manager - -

Check what is listening on port 748

Linux: is anything listening on TCP 748?
sudo ss -tlnp 'sport = :748'
Linux: UDP 748
sudo ss -ulnp 'sport = :748'
Linux / macOS: which process owns the port
sudo lsof -nP -i :748
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':748 '
Windows (Command Prompt)
netstat -ano | findstr :748
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 748 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 748
From Windows
Test-NetConnection HOST -Port 748
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 748

Block port 748 in the firewall

ufw
sudo ufw deny 748/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 748 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 748 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 748' -Direction Inbound -Protocol TCP -LocalPort 748 -Action Block
ufw
sudo ufw deny 748/udp
iptables
sudo iptables -A INPUT -p udp --dport 748 -j DROP
nftables
sudo nft add rule inet filter input udp dport 748 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 748' -Direction Inbound -Protocol UDP -LocalPort 748 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.