> On Jun 25, 2020, at 8:05 PM, Michael Knill
> <michael.kn...@ipcsolutions.com.au> wrote:
>
> Hi Group
>
> I have changed my internet provider and I am having connectivity problems to
> some sites on Astlinux.
> I am fairly certain that it is an MTU/MSS issue as I have fixed it on my
> Mikrotik router by adjusting this value.
> Funny that I'm having problems with this provider but not on my previous
> provider. Both are using PPPoE and I tested that the maximum MTU for both is
> 1464 e.g.
>
> 3035-JSainsbury-CM1 kd # fping -M -b 1465 12000.ipcaccess.net
> 12000.ipcaccess.net: error while sending ping: Message too long
> 3035-JSainsbury-CM1 kd # fping -M -b 1464 12000.ipcaccess.net
> 12000.ipcaccess.net is alive
>
> 3076-VisionCF-CM1 kd # fping -M -b 1465 12000.ipcaccess.net
> 12000.ipcaccess.net: error while sending ping: Message too long
> 3076-VisionCF-CM1 kd # fping -M -b 1464 12000.ipcaccess.net
> 12000.ipcaccess.net is alive
>
> Maybe my new provider is not allowing fragmentation?
>
> Anyway just wondering how I fix this problem. Do I just set MTU using IFMTU
> in user.conf? E.g.
> IFMTU=ppp0:1460
No, per the /stat/etc/rc.conf file:
--
## MTU Changes
## If you need to specifically set the MTU for a given interface, do that here.
## You can try to set the MTU for any valid type of interface. With ethernet it
## works most of the time. Everything else, caveat emptor...
## If you are using PPPoE don't worry. We automatically handle those MTU issues
#IFMTU="eth2.41:1496 eth0:1492"
--
I don't see any configuration for the PPPoE MTU, though there may be a way.
What is the local MTU set to by default ?
--
ip link show dev ppp0
--
After the PPPoE link is up you could try to change it:
--
ip link set dev ppp0 mtu 1460
--
If that works we can try to figure out how to make that stick.
> Can I set the TCP MSS anywhere?
This is the current value hardcoded in the PPPoE config:
CLAMPMSS=1412
-- PPPoE docs --
CLAMPMSS
The value at which to "clamp" the advertised MSS for TCP sessions. The default
of 1412 should be fine.
--
Lonnie
>
> Regards
> Michael Knill
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