On Wed, Dec 3, 2008 at 2:37 PM, Vu Pham <span dir="ltr"><<a href="mailto:vu@sivell.com">vu@sivell.com</a>></span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>
I have a network printer using LPD. When I *manually* telnet to that printer at LPD port, then the printer does ACK to my SYN packet and start receiving data.<br>
<br>
When I use CUPS to print, then the printer does not acknowledge the tcp SYN packets at all.<br>
<br>
They are just TCP connections, how does the printer know ? :(<br>
Below is my tcpdump:<br>
All packets before 14:24:54 are from my manual telnet.<br>
All packets after 14:25:06 are from CUPS.<br>
Pluto is my server, <a href="http://192.168.1.110" target="_blank">192.168.1.110</a> is the printer<br>
<br>
As you can see, CUPS attempted to send SYN packets but does not get ACKED.<br>
<br>
I can only see the difference of the source ports, but does the printer care about that ?<br>
<br>
-------------- start of tcpdump -------<br>
[root@jetco ~]# tcpdump host <a href="http://192.168.1.110" target="_blank">192.168.1.110</a><br>
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode<br>
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes<br>
14:24:50.555796 IP pluto.51602 > 192.168.1.110.printer: S 3462708113:3462708113(0) win 5840 <mss 1460,nop,nop,sackOK,nop,wscale 2><br>
14:24:50.764192 IP 192.168.1.110.printer > pluto.51602: S 3520144456:3520144456(0) ack 3462708114 win 4096 <mss 1452,nop,wscale 0><br>
14:24:50.764207 IP pluto.51602 > 192.168.1.110.printer: . ack 1 win 1460<br>
14:24:54.396898 IP pluto.51602 > 192.168.1.110.printer: F 1:1(0) ack 1 win 1460<br>
14:24:54.409157 IP 192.168.1.110.printer > pluto.51602: . ack 2 win 4380<br>
14:24:54.409700 IP 192.168.1.110.printer > pluto.51602: F 1:1(0) ack 2 win 4380<br>
14:24:54.409714 IP pluto.51602 > 192.168.1.110.printer: . ack 2 win 1460<br>
<br>
<br>
<br>
14:25:06.560950 IP pluto.731 > 192.168.1.110.printer: S 3473251429:3473251429(0) win 5840 <mss 1460,nop,nop,sackOK,nop,wscale 2><br>
14:25:09.560695 IP pluto.731 > 192.168.1.110.printer: S 3473251429:3473251429(0) win 5840 <mss 1460,nop,nop,sackOK,nop,wscale 2><br>
14:25:15.560267 IP pluto.731 > 192.168.1.110.printer: S 3473251429:3473251429(0) win 5840 <mss 1460,nop,nop,sackOK,nop,wscale 2><br>
-------------- end of tcpdump -------<br>
<br>
Any advice, please ?<br>
<br>
Thanks,<br>
<br>
Vu<br>
_______________________________________________</blockquote><div><br>Doesn't CUPS use IPP port by default? Could this be the problem?<br><br>Andrew <br></div></div><br>