CyberHunter
LinkedIn profile - Bastien Cordier Email: contact@bastiencordier.pro
// Network services

Port 3503: MPLS LSP-echo Port

Port 3503 is assigned by IANA to lsp-ping (MPLS LSP-echo Port).

3503

How lsp-ping works

Network services
client:3503lsp-pingresponse client:3503lsp-pingresponse

The client sends a request to port 3503 and the lsp-ping service answers.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
Network services
01 Security

Is port 3503 dangerous?

We have no specific security note for port 3503. Its risk depends on the program actually listening on it. General advice for network services services:

  • Answer only the networks that need the service (no open resolvers, relays or reflectors).
  • UDP services can be abused for DDoS amplification: rate-limit or block them at the edge.
  • Disable legacy test services that have no use in production.
02 Registry

IANA registry entries for port 3503

ServicePortTransportDescriptionReferenceUpdated
lsp-ping 3503 TCP, UDP MPLS LSP-echo Port RFC 8029 -

// source: IANA service name and port number registry

03 Check it

Which program uses port 3503, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3503'      # process listening on 3503
sudo lsof -nP -i :3503

macOS

sudo lsof -nP -i :3503

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3503 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3503
netstat -ano | findstr :3503

From another machine

nmap -p 3503 -sV <host>
sudo nmap -sU -p 3503 <host>
nc -zv <host> 3503

Block it in the firewall

sudo ufw deny 3503/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3503" -Direction Inbound -LocalPort 3503 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3503 used for?

Port 3503 is assigned by IANA to lsp-ping (MPLS LSP-echo Port).

Is port 3503 TCP or UDP?

Port 3503 is registered for TCP and UDP.

Is it safe to open port 3503?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Answer only the networks that need the service (no open resolvers, relays or reflectors).

How do I check if port 3503 is open?

On Linux run "ss -ltnup 'sport = :3503'", on macOS "lsof -nP -i :3503", and on Windows "netstat -ano | findstr :3503" to see the local process. From another machine, "nmap -p 3503 <host>" shows whether it is reachable.

05 Related
:53 DNS tcp · udp · moderate risk :135 MS RPC tcp · udp · high risk :123 NTP udp · tcp · moderate risk :67 DHCP server udp · tcp · moderate risk :111 rpcbind tcp · udp · high risk :9100 Raw printing (JetDirect) tcp · udp · high risk :631 IPP / CUPS tcp · udp · high risk :5353 mDNS udp · tcp · moderate risk

Latest vulnerability news

All news