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I have noticed during port scanning that my "anonymous" IP has an open port (111) while I am using VPN.

Does this make me vulnerable as user or is it the provider's failure? Should I change providers or do I have nothing to worry about (since, if the providers' network security is compromised, mine is in risk as well)?

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NOTE: All of this assumes you are talking about TCP 111 (vs UDP).

If you are using a VPN service, you are sharing that Public IP with many customers and being NAT'd somewhere along the way. This Public IP is generally not directly routable to you as a user of the service, as such, there isn't much to worry about.

That being said, it's hard to know (without more info/probing) exactly what is running on that open port. In general, ports 1-1023 fall in the Well-Known Ports range, though that's not to say that something else can't be running on this port, but it's likely an RPC (remote procedure call) service like SunRPC.

TL; DR You're probably fine, but if you're still worried about, contact the VPN vendor and ask them exactly what it is and what it's used for.

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The port might be consumed by rpcbind. What rpcbind does, is described here

An excerpt:

When a client signs up for a given interface on a particular host, usually with a clnt_create() call, the stub code asks rpcbind on that host a question, something like "on what UDP or TCP port is protocol number X listening?" rpcbind, unlike most other ONC services, listens on TCP and UDP port 111, so given a host name or IP address, a program can just ask rpcbind on that host or IP address. rpcbind responds with the appropriate port number, if a server has registered with it on that host. That registration is done by the server process when it calls svc_create().

  • This will give you your TCP/UDP 111, the OP asked about the IP address he's presenting as. – HashHazard Jul 15 '16 at 21:35
  • fair. modified the answer to be more specific – sandyp Jul 15 '16 at 21:49

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