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I'm trying to debug a connection issue with network printer that is refusing to connect to a specific smtp server. While capturing from the same switch that the printer is connected to I can see packets coming up and down but, even smtp communication with "other smtp servers" but NOT to this particular one. the smtp server is alive as I can ping it and telnet it to port 25, and I can even send mails from email clients and all this will be visible with wireshark, not the failed connection to the problematic smtp.server4 I found that when the printer connect to the other smtp servers the packet length is 1514 so I suspected an mtu issue, but shouldn't I be able to see the the requests from mac source at least?

asked 31 Jan '12, 06:37

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D10221
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edited 31 Jan '12, 09:20

Is the printer configured with the SMTP server's name, or its IP address? If name, do you see a DNS query from the printer? If so, does it get a successful response?

Do you see an ARP request from the printer for the SMTP server's IP address? (You might need to power-cycle the printer in order to clear its ARP cache.)

1,514 bytes is a common frame size on networks that do not have jumbo frames enabled, so it's probably not an MTU issue.

(31 Jan '12, 13:11) Jim Aragon

Thanks jim, ip or host name made no difference, I can see http,icmp,and the printer services,even ipx traffic and arp traffic just before the smtp functions, and i can confirm from my laptop the smtp server won't answer pings with packets larger than 1464 bytes. no arp request seen from the moment I try smtp application until I use other services (http,ping,etc)

(31 Jan '12, 19:25) D10221

The real and deep reason why I couldn't see the specific smtp packets is still escaping to me, but it was solved hooking up an old hub instead of a switch.

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answered 01 Feb '12, 07:03

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D10221
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question asked: 31 Jan '12, 06:37

question was seen: 4,329 times

last updated: 01 Feb '12, 07:03

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