|Yes, there are ways to *mostly* tell. No, they're not easy. |
For L3 filtering you could try an ICMP ping & see if you're blocked by IP addy...ICMP's could be filtered tho...could also try from a proxy to see if you're being blocked by source ip
TCP connectivity could be checked by looking at responses to your SYN -- if SYN gets no RST then it's probably filtered & being dropped instead of replying with an RST...could also mean the host is just down...
If you're blocked at HTTP level, then socket might open & then immediately close or could serve an HTTP 403.
Bottom line is, I can't really tell you how to check this without going into pages and pages of details. You should download Wireshark, it's a good packet capture/analysis program. Study the protocols & try to make sense of what's actually happening.