ping alternative for tcp?
Regardless of the fact that TCP can tolerate packet-loss/packet-ordering issues, a ping loss of 30% is still quite significant if the "population" is large enough - i.e., more than say 100 pings.
But to answer the question, you can look at nmap. I'm sure examples will come flooding in shortly :)
More importantly though, you don't want just a round-trip time, you really want to see the performance from your machine to the server and back at every (possible) hop.
You can do this with traceroute - however the most commonly found version of this is done using ICMP or UDP, but search for tcp traceroute - and start there.
Here are some fun tools to try while you're at it...
- lft
- paketto
- hping
Here's an example with lft...
% lft -S 4.2.2.2
Hop LFT trace to vnsc-bak.sys.gtei.net (4.2.2.2):80/tcp
1 ln-gateway.centergate.com (206.117.161.1) 0.5ms
2 isi-acg.ln.net (130.152.136.1) 2.3ms
3 isi-1-lngw2-atm.ln.net (130.152.180.21) 2.5ms
4 gigabitethernet5-0.lsanca1-cr3.bbnplanet.net (4.24.4.249) 3.0ms
5 p6-0.lsanca1-cr6.bbnplanet.net (4.24.4.2) 3.4ms
6 p6-0.lsanca2-br1.bbnplanet.net (4.24.5.49) 3.3ms
7 p15-0.snjpca1-br1.bbnplanet.net (4.24.5.58) 10.9ms
8 so-3-0-0.mtvwca1-br1.bbnplanet.net (4.24.7.33) 11.1ms
9 p7-0.mtvwca1-dc-dbe1.bbnplanet.net (4.24.9.166) 11.0ms
10 vlan40.mtvwca1-dc1-dfa1-rc1.bbnplanet.net (128.11.193.67) 11.1ms
** [neglected] no reply packets received from TTLs 11 through 20
** [4.2-3 BSD bug] the next gateway may errantly reply with reused TTLs
21 [target] vnsc-bak.sys.gtei.net (4.2.2.2) 11.2ms
Netcat Power Tools describes how to do TCP Ping with netcat. Specifically, every unsolicited ACK packet should return RST.
I'm personally a big fan of mtr ( http://www.bitwizard.nl/mtr/ ), mtr is an ncurses based traceroute clone which can work using both icmp and udp. It shows you the weak spots in your link to a certain host and is in that way non intrusive.
When it really comes to some load tests I would go with iperf (which is client/server).