TTL signal

FTP uses two TCP connections: a control channel and a data channel. The control channel is used for sending commands and receiving status responses. The data channel is used for sending and receiving data (files, and directory listings).

The control channel is established by the client connecting to the server. In the original FTP implementation, the data channel was established by the server connecting back to the client (i.e. the client is the "server" end of the data connection).

This doesn't work with some firewalls, which block inbound connections unless specifically told otherwise. Passive (PASV) mode is an extension to the FTP protocol which allows the data channel to be established by the client connecting to the server.

It works for me, but that may just be that my firewall is more lenient than Phil's. Some firewalls have explicit support for (non-passive) FTP. They recognise FTP control channels (port 21), and monitor the traffic. When the client tells the server to connect back to it on a specific port, they add a temporary "exemption" to allow the FTP server to connect to that port.

ftp://jjlarkin.lmi.net/3ns_TTL.jpg

On a sunny day (Thu, 18 Dec 2008 07:27:22 -0800) it happened John Larkin wrote in :

That is very simple: grml: ~ # host 66.117.156.8

8.156.117.66.in-addr.arpa domain name pointer jjlarkin.lmi.net.

So, in your browser type: ftp://jjlarkin.lmi.net/3ns_TTL.jpg

Hmm. Maybe it's a firewall issue then. In any case, I can help with the second problem:

I:\\>nslookup 66.117.156.8 Server: yktns1.watson.ibm.com Address: 9.2.250.86

Name: jjlarkin.lmi.net Address: 66.117.156.8

Cheers,

Phil Hobbs

"Name Server Lookup" in NetScanTools v4.02

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food

Cool. Thanks.

John

Neat. I don't consider all this protcol/path/port sort of stuff to be "electronics", and I haven't bothered to understand much of it... just enough to get my Ethernet instruments to talk. There's plenty of real stuff to keep up with.

I'll ping my guys at LMI and see if they can turn on the PASV thing without breaking something else. Which they usually do.

John

$ whois 66.117.156.8

OrgName: LanMinds, Inc. OrgID: LANM Address: 1700 Martin Luther King Jr. Way City: Berkeley StateProv: CA PostalCode: 94709 Country: US

NetRange: 66.117.128.0 - 66.117.159.255 CIDR: 66.117.128.0/19 NetName: LOCRIAN-ENTERPRISES NetHandle: NET-66-117-128-0-1 Parent: NET-66-0-0-0-0 NetType: Direct Allocation NameServer: NS2.LMI.NET NameServer: NS3.LMI.NET Comment: RegDate: 2002-10-09 Updated: 2005-03-07

OrgAbuseHandle: ABUSE37-ARIN OrgAbuseName: Abuse OrgAbusePhone: +1-510-843-6389 OrgAbuseEmail: snipped-for-privacy@lmi.net

OrgNOCHandle: NOC140-ARIN OrgNOCName: Network Operations Center OrgNOCPhone: +1-510-843-6389 OrgNOCEmail: snipped-for-privacy@lmi.net

OrgTechHandle: NOC140-ARIN OrgTechName: Network Operations Center OrgTechPhone: +1-510-843-6389 OrgTechEmail: snipped-for-privacy@lmi.net

OrgTechHandle: GM41-ARIN OrgTechName: Morrell, Gary OrgTechPhone: +1-510-843-6389 OrgTechEmail: snipped-for-privacy@lmi.net

# ARIN WHOIS database, last updated 2008-12-17 19:10 # Enter ? for additional hints on searching ARIN's WHOIS database.

Cheers! Rich

Hi, Phil,

I asked my ISP guys to enable PASV, and they replied that PASV is the responsibility of the client, not the server, and they demonstrated that they could access my site in PASV mode. They say...

"PASV or passive mode is a setting in the ftp client not on the server. Some web browser's ftp clients are severely broken -cough- Internet Exploder -cough. They might need to use a stand alone ftp client."

Hey, I tried.

John

John,

Thanks. My FTP server has settings to enable/disable both active and passive FTP. If it's switched on at their end, it's probably a firewall issue.

Cheers,

Phil Hobbs

PASV seems to be enabled now.

jasen@gonzo:~$ ftp 66.117.156.8 Connected to 66.117.156.8.

220 jjlarkin.lmi.net FTP server (Version wu-2.6.2(1) Wed Dec 5 16:35:31 PST 2001) ready. Name (66.117.156.8:jasen): ftp 331 Guest login ok, send your complete e-mail address as password. Password: 230 Guest login ok, access restrictions apply. Remote system type is UNIX. Using binary mode to transfer files. ftp> passive Passive mode on. ftp>

Also I don't recall ever having a problem using seamonkey to view his files.

OTOH I can't get to jamie6" 's web site, my ISP is blocking traffic to that ip-address block and gives me some line of bullshit when I ask them about it.