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ToddInDavis's profile

2 Messages

Wednesday, February 21st, 2024 7:53 PM

Is port 111 network traffic blocked?

I am trying to use the Portmapper service (on port 111) on an Ubuntu computer in Microsoft's Azure cloud service. I can login via SSH, and try to connect to ports 110, 112, and 114 (all properly rejected as expected), but connection attempts to port 111 time out.

When I am connected through Xfinity, I can connect to port 111.

Is AT&T blocking outbound (from home) connections to port 111?

ACE - Expert

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35.6K Messages

3 months ago

AT&T does not mention 111 in its list of ports that it suppresses in its network management policies (see https://about.att.com/sites/broadband/network ).  Perhaps you have an IP-based filter on that port in your Traffic Security Management rules?

2 Messages

3 months ago

I'm a little disappointed to see how many protocols AT&T blocks. I recognize the security need, but it can also break a lot of legitimate functionality.

Is the blocking done at the edge as the packets leave the customer's router and into the AT&T fabric, or throughout the fabric itself?

If it is done as the packets leave the customers' router, can we apply for an exception to allow some traffic to leave our routers?

(By the way, I used tcpdump on the destination Linux box and confirmed it received packets on ports 109, 110, 112, and 113 but not port 111. AT&T is doing some blocking somewhere along the line)

ACE - Expert

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35.6K Messages

3 months ago

(By the way, I used tcpdump on the destination Linux box and confirmed it received packets on ports 109, 110, 112, and 113 but not port 111. AT&T is doing some blocking somewhere along the line)

May I assume that you've also checked your Azure NSG rules to ensure that it's not being done, per your request, by Azure.  Also check that there's not a port filter rule defined in your Gateway, just to cover all the bases.  AT&T documents enough blocked protocols and ports that I'd be surprised that there's one they forgot to mention or are hiding.

Is the blocking done at the edge...

I'm not sure where the traffic management is done, but somewhere further along than the Gateway itself.  You can try to ask support to quit filtering a port that they say that they're not filtering.  But you'd first have to talk to someone with some idea of what you're talking about, and that'll take a day.  Then they won't know who to pass such a request on to.  For a consumer account, this road will be long and hard, and I don't expect any success, assuming that they're actually blocking it at all.  If you get a dedicated enterprise account, the paths are much more open.

3 Messages

3 months ago

Port 111 is typically used for the RPC (Remote Procedure Call) protocol, which is used for network file system operations on Unix and Linux systems. To check if port 111 is blocked, you can use the following command in a terminal window:

phpCopy code
telnet <hostname_or_ip> 111

If the connection fails, it's possible that port 111 is blocked. You can also use a port scanning tool like Nmap to scan for open ports on the target system.

Before unblocking port 111, consider the security implications and ensure that you have proper firewall rules in place to protect your system.

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