A question about MTU

I've been having lots of trouble with my ADSL connection lately,
roughly once a day the DSL signal drops out completely and I can only
re-establish it by phoning the landline from my mobile.

I sent an extract of my router's logfile to my ISP. A section of it
is:


01:02:21 DSL Carrier is down

01:02:41 DSL Carrier is down

01:02:51 DSL Carrier is up

01:02:57 Couldn't increase MTU to 1500

01:02:57 Connection terminated.

01:02:57 pppd 2.4.1 started by root, uid 0

01:02:57 Connect: ppp0 {--}

01:02:57 Couldn't increase MTU to 1500

01:03:00 First get lcp

01:03:01 PPPoA Connect with IP Address 62.53.79.247

01:03:01 PPPoA Connection Successfully Established


They have replied saying I should set the MTU to 1458 but upon checking
I have found that it is already set at 1458 bytes. So my questions are

- what is MTU?
- why would a logfile include the line "couldn't increase MTU to 1500"
when the MTU is set at 1458?

--
Abso [at] ukrm [dot] net

The FAQ for upce is at http://upce.org.uk and http://ebayfaq.co.uk

On 4 Aug 2004 18:11:17 GMT, "Abso" <(E-Mail Removed)> wrote:

>I've been having lots of trouble with my ADSL connection lately,
>roughly once a day the DSL signal drops out completely and I can only
>re-establish it by phoning the landline from my mobile.
>
Have a look here http://www.dslreports.com/tools

On Wed, 04 Aug 2004 18:11:17 +0000, Abso wrote:

> I've been having lots of trouble with my ADSL connection lately, roughly
> once a day the DSL signal drops out completely and I can only
> re-establish it by phoning the landline from my mobile.
>
> I sent an extract of my router's logfile to my ISP. A section of it is
<snip>
>
> They have replied saying I should set the MTU to 1458 but upon checking
> I have found that it is already set at 1458 bytes. So my questions are
>
> - what is MTU?
> - why would a logfile include the line "couldn't increase MTU to 1500"
> when the MTU is set at 1458?

What make of router do you have? Dlink? If it is a Dlink then the answer
is that Dlink don't have a well engineered product.

My Dlink doesn't set the MTU, instead it sets the MRU (Maximum Receive
Unit). So my dlink sends packet's out that 1500 bytes long, the remote
site sends packets back that are 1500 bytes long. Because my MRU is 1430,
then my Dlink drops the packet. This only affected some sites.

Telnet onto your router and set the MTU of ppp0 to 1430 manually.
(root/admin are the most likely username/passwords).
The command you need is:
ifconfig ppp0 mtu 1430


Regards,
Adam

Adam wrote:

> On Wed, 04 Aug 2004 18:11:17 +0000, Abso wrote:
>
> > I've been having lots of trouble with my ADSL connection lately,
> > roughly once a day the DSL signal drops out completely and I can
> > only re-establish it by phoning the landline from my mobile.
> >
> > I sent an extract of my router's logfile to my ISP. A section of
> > it is
> <snip>
> >
> > They have replied saying I should set the MTU to 1458 but upon
> > checking I have found that it is already set at 1458 bytes. So my
> > questions are
> >
> > - what is MTU?
> > - why would a logfile include the line "couldn't increase MTU to
> > 1500" when the MTU is set at 1458?
>
> What make of router do you have? Dlink? If it is a Dlink then the
> answer is that Dlink don't have a well engineered product.

No, it's a Netgear DG632.

> My Dlink doesn't set the MTU, instead it sets the MRU (Maximum Receive
> Unit). So my dlink sends packet's out that 1500 bytes long, the remote
> site sends packets back that are 1500 bytes long. Because my MRU is
> 1430, then my Dlink drops the packet. This only affected some sites.
>
> Telnet onto your router and set the MTU of ppp0 to 1430 manually.

Well I've set the MTU to 1430 via the Netgear's webpage interface just
for the hell of it, to see what happens.

FWIW I think I've found the source of my ongoing ADSL problems.
Earlier I disconnected everything from the line except a single
analogue telephone. Lifting the receiver it was noticable that there
was a mass of crackles and pops on the line. I haven't noticed this
before as I rarely connect a phone or use it (I make and receive all
calls on my mobile).

Would this explain the kind of trouble I described up there ^ ?

I've reported the fault to BT but in the past 3 months I've had to
report 3 faults and each time they've concluded that there was no
problem. Grrr.


--
Abso [at] ukrm [dot] net

The FAQ for upce is at http://upce.org.uk and http://ebayfaq.co.uk

On Thu, 05 Aug 2004 20:25:35 +0000, Abso wrote:

> Adam wrote:

>> What make of router do you have? Dlink? If it is a Dlink then the answer
>> is that Dlink don't have a well engineered product.
>
> No, it's a Netgear DG632.
>

Looks *EXACTLY* the same as my DLINK logs- but I'm not that sruprised
about that.

>> My Dlink doesn't set the MTU, instead it sets the MRU (Maximum Receive
>> Unit). So my dlink sends packet's out that 1500 bytes long, the remote
>> site sends packets back that are 1500 bytes long. Because my MRU is
>> 1430, then my Dlink drops the packet. This only affected some sites.
>>
>> Telnet onto your router and set the MTU of ppp0 to 1430 manually.
>
> Well I've set the MTU to 1430 via the Netgear's webpage interface just for
> the hell of it, to see what happens.
>
> FWIW I think I've found the source of my ongoing ADSL problems. Earlier I
> disconnected everything from the line except a single analogue telephone.
> Lifting the receiver it was noticable that there was a mass of crackles
> and pops on the line. I haven't noticed this before as I rarely connect
> a phone or use it (I make and receive all calls on my mobile).
>
> Would this explain the kind of trouble I described up there ^ ?
>
> I've reported the fault to BT but in the past 3 months I've had to report
> 3 faults and each time they've concluded that there was no problem. Grrr.

Not sure, but the dummy mode first-line support question is.... do you
have micro-filters installed... (followed by some method of getting you
off the phone so that it becomes someone elses problems ;-).

I always try avoid the physical layer of comms whenever I can- so not much
help I'm afraid.

--
Regards,
Adam Allen.

PGP: http://pgp.mit.edu:11371/pks/lookup?...e.net&op=index