How to check open TCP port in Cisco IOS

[AndreyPokorskiy]

Hello Cisco Community
Client asked us to check if Cisco switch could get access to DNS over TCP/UDP ports
I used telnet x.x.x.x 53 (or domain)
It could confirm that the port TCP 53 is opened or not
My question is:
Is there any way how to send request to check UDP or TCP port from Cisco IOS?

Thank you!

[IP_Cartel]

try this document: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr_dns/configuration/15-mt/dns-15-mt-book/dns-config-dns.html

it talks about DNS.

[MHM Cisco World]

the telnet result is show if port is open or not,
I do small lab, I config R3 vty line with password 
and config NAT in R1 223->23 port 
and I config deny acl in R1 for port 223

I now telnet from R2 to R3 using 223 port, and as you see the destination unreachable!!! this meaning that port is close in way from R2 to R3 (close in R1 since I config ACL deny tcp 223 port).

so it depend on result you get from telnet.