# Ping.pingecho **URL:** \ **Category:** Ruby\ **Created:** [August 29, 2008, 5:51pm UTC](https://www.ruby-forum.com/t/ping-pingecho/147232 "2008-08-29T17:51:13Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![john\_maclean](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@john\_maclean](https://www.ruby-forum.com/u/john_maclean)\ **Post date:** [August 29, 2008, 5:51pm UTC](https://www.ruby-forum.com/t/ping-pingecho/147232/1 "2008-08-29T17:51:13Z")
[Cisco.com](http://Cisco.com) don’t normally allow pings so tracroutes and pings won’t get echo requests. irb(main):003:0\> Ping.pingecho(‘[cisco.com](http://cisco.com)’, 10, 80) =\> true How come this works and `ping` does not? From irb I see that Ruby’s ping uses a TCP echo. Also I’ve run tcpdump whilst running ping.echo and could not determine the port that it uses. What port does Ruby’s Ping use? ---
**Author:** ![john\_maclean](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@john\_maclean](https://www.ruby-forum.com/u/john_maclean)\ **Post date:** [August 29, 2008, 5:56pm UTC](https://www.ruby-forum.com/t/ping-pingecho/147232/2 "2008-08-29T17:56:24Z")
john maclean wrote: > [Cisco.com](http://Cisco.com) don’t normally allow pings so tracroutes and pings won’t get > echo requests. > > irb(main):003:0\> Ping.pingecho(‘[cisco.com](http://cisco.com)’, 10, 80) > =\> true > > How come this works and `ping` does not? From irb I see that Ruby’s > ping uses a TCP echo. Also I’ve run tcpdump whilst running ping.echo > and could not determine the port that it uses. What port does Ruby’s > Ping use? check out: [http://www.noobkit.com/show/ruby/ruby/standard-library/ping/pingecho.html](http://www.noobkit.com/show/ruby/ruby/standard-library/ping/pingecho.html) According to this the ‘echo’ port. grep’ing ‘echo’ in my /etc/services reveals this is port 7…apparently. (UDP and TCP). ---
**Author:** ![john\_maclean](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@john\_maclean](https://www.ruby-forum.com/u/john_maclean)\ **Post date:** [August 30, 2008, 7:23am UTC](https://www.ruby-forum.com/t/ping-pingecho/147232/3 "2008-08-30T07:23:40Z")
2008/8/29 John Pritchard-williams [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > > and could not determine the port that it uses. What port does Ruby’s > > – > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). Thanks for the reply. pinging on the echo port makes sense. However one can ping a host for service and get a response even if that service is not actually running on the host. services = %w{bacula-dir distcc echo fax git hostname http https icmpd kermit keyserver ldap mbus msexch-routing mysql nmap postgres quake rsync rwhois shell squid ssh svn telnet traceroute tunnel whoami wins x11} wooota = ‘192.168.1.1’ services.each do |x| p %Q{checking host #{host} for protocol #{x}} p Socket.getaddrinfo(host, x) end I get responses even though I **know** that these services are **not** running on my router. Is this because pingecho sends packets on port 7 regardless of the service that one requests? ---
**Author:** ![john\_maclean](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@john\_maclean](https://www.ruby-forum.com/u/john_maclean)\ **Post date:** [August 30, 2008, 7:10pm UTC](https://www.ruby-forum.com/t/ping-pingecho/147232/4 "2008-08-30T19:10:59Z")
john maclean wrote: > > > ping uses a TCP echo. Also I’ve run tcpdump whilst running ping.echo > > end > > I get responses even though I **know** that these services are **not** > running on my router. Is this because pingecho sends packets on port 7 > regardless of the service that one requests? getaddrinfo doesn’t do what you think it does. All it does is resolve the hostname you give it and translate the english name of the port into the port number by looking it up in /etc/services (or similar). It doesn’t actually try to open a TCP connection to that host to determine if that port is open. Also, a “TCP ping” is an attempt to determine if a host is up by doing something like sending it a connection request. If the connection request is either allowed (SYN/ACK) or denied (RST), you know the host is up. This is unreliable as many hosts drop connection requests on ports that are closed, but is a good method of determining if a host is up if they block ICMP. When you use Ping.pingecho on a host that drops packets instead of sending RST, be sure to specify a port you know is open. ---
**Author:** ![john\_maclean](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@john\_maclean](https://www.ruby-forum.com/u/john_maclean)\ **Post date:** [August 30, 2008, 1:48pm UTC](https://www.ruby-forum.com/t/ping-pingecho/147232/5 "2008-08-30T13:48:29Z")
On Fri, Aug 29, 2008 at 11:01 PM, john maclean [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > ping uses a TCP echo. Also I’ve run tcpdump whilst running ping.echo > > > (UDP and TCP). > > > service is not actually running on the host. > > > p Socket.getaddrinfo(host, x) > > > end > > I get responses even though I **know** that these services are **not** > running on my router. Is this because pingecho sends packets on port 7 > regardless of the service that one requests? I suspect the zeroth entry doesn’t mean anything, just that the command ran without error. For example, try Socket.getaddrinfo(‘0.0.0.0’, ‘smtp’). Todd