Digital Subscriber Line Verizon DSL - SMTP Problems with Linksys Router

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Subject Author Date
Verizon DSL - SMTP Problems with Linksys Router Kevin G. 06-28-06
Posted by Kevin G. on June 28, 2006, 3:16 pm
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Hello all,

I'm working for a customer who has Verizon DSL here in Pennsylvania,
and they want to go wireless in their offices. So I set the customer
up with a Linksys WRT54G compact router. Now I've set Linksys routers
up dozens of times before, with relatively no problems.

Now the first tricky thing with the Verizon Westel hardware is that it
uses the 192.168.1.1 for its own internal admin -- so the Linksys setup
wizard was smart enough to use 192.168.2.1 for the Linksys admin. So
the router is now setup and connected to the DSL modem, and I do have
an outgoing connection to the internet while plugged into the router.

However, the oddest thing is now happening when I try to send email
from the customer's email client. The email client (outlook express)
does login to the SMTP server as it should be, and passes
authentication -- but then when it tries to send the outgoing mail, it
never quite finishes and just times out eventually. BUT... when
plugged directly into the Westel DSL modem, this problem does NOT exist
--- it's only when plugged into the Linksys WRT54G.

Verizon does require user authentication with their outgoing SMTP, and
the settings in the email client ARE correct. So that's not the
problem here --- the problem seems to be a port 25 issue when connected
to the router.

I've logged into the router admin countless times now, and disabled the
internal firewall. I've also disabled the computer's firewall to make
sure it wasn't on the PC side --- but this strange outgoing mail
problem still remains.

Has anyone seen this before with a Verizon DSL connection connected to
a router?? Any suggested settings on the router side to make sure
outgoing port 25 traffic flows??

Many thanks in advance,
KG


Posted by DLR on June 29, 2006, 7:57 am
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... big snip ...

> However, the oddest thing is now happening when I try to send email
> from the customer's email client. The email client (outlook express)
> does login to the SMTP server as it should be, and passes
> authentication -- but then when it tries to send the outgoing mail, it
> never quite finishes and just times out eventually. BUT... when
> plugged directly into the Westel DSL modem, this problem does NOT exist
> --- it's only when plugged into the Linksys WRT54G.

... small snip ...

> Has anyone seen this before with a Verizon DSL connection connected to
> a router?? Any suggested settings on the router side to make sure
> outgoing port 25 traffic flows??

You may need to set the MTU from 1500 to 1492. And the only time you'll
see this issue if you're sending OUT something larger than 1490 bytes or
so. Which is why emails trigger the issue.

Posted by Kevin G. on June 29, 2006, 12:41 pm
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> You may need to set the MTU from 1500 to 1492. And the only time you'll
> see this issue if you're sending OUT something larger than 1490 bytes or
> so. Which is why emails trigger the issue.

DLR.... are you saying change the MTU on the Windows machine? Or
within the router admin? I've messed with MTU settings in the Windows
registry before, but not sure if the Linksys routers have MTU numbers
hard-coded or not.

Please let me know when you get a minute...

KG


Posted by DLR on June 29, 2006, 3:20 pm
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Kevin G. wrote:
>> You may need to set the MTU from 1500 to 1492. And the only time you'll
>> see this issue if you're sending OUT something larger than 1490 bytes or
>> so. Which is why emails trigger the issue.
>
> DLR.... are you saying change the MTU on the Windows machine? Or
> within the router admin? I've messed with MTU settings in the Windows
> registry before, but not sure if the Linksys routers have MTU numbers
> hard-coded or not.
>
> Please let me know when you get a minute...
>
Inside the router. That's where it matters. It's for whatever device is
connecting to the modem.

And I have no idea why it might be wrong but I've had to deal with this
on two Linksys routers recently.

Posted by Kevin G. on June 29, 2006, 9:26 pm
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DLR wrote:
> Kevin G. wrote:
> >> You may need to set the MTU from 1500 to 1492. And the only time you'll
> >> see this issue if you're sending OUT something larger than 1490 bytes or
> >> so. Which is why emails trigger the issue.
> >
> > DLR.... are you saying change the MTU on the Windows machine? Or
> > within the router admin? I've messed with MTU settings in the Windows
> > registry before, but not sure if the Linksys routers have MTU numbers
> > hard-coded or not.
> >
> > Please let me know when you get a minute...
> >
> Inside the router. That's where it matters. It's for whatever device is
> connecting to the modem.
>
> And I have no idea why it might be wrong but I've had to deal with this
> on two Linksys routers recently.

Alright.... changed the MTU down to 1492 in the router, and saved the
changes. Still can't send any outgoing mail over SMTP port 25 :( I
also tried 1400, and 1300 for the MTU -- no good either.

I also tried matching the MTU of the Windows machine to the router's
1492 setting, then rebooted for registry entries to take effect---
still no good. So I'm seriously at a loss here. Any other possible
suggestions on this one???


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