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Bug #13070

mtu option too large MTU 1728 - 1500

Added by gh origin 3 months ago. Updated 3 months ago.

Status:
New
Priority:
High
Assignee:
-
Category:
-
Start date:
Due date:
% Done:

0%

Estimated time:
Difficulty:
Medium
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Gerrit CR:

Description

This error is printed on each boot. I'm using a Realtek Ethernet card and on Linux the MTU is always set to 1500.

It's not just annoying but this bug also caused poor network performance on my system. On Linux, I could get into 11 Mb/s as the maximum but I found I could only get to 1.6 Mb/s maximum on Illumos.

I wanted to use Illumos to host Linux VMs but currently I can't because the network speed is too bad.

Please have a look at this issue. Thanks.

#1

Updated by gh origin 3 months ago

This fixed the network speed:

sudo ndd -set /dev/tcp tcp_wscale_always 1
sudo ndd -set /dev/tcp tcp_tstamp_if_wscale 1
sudo ndd -set /dev/tcp tcp_max_buf 33554432
sudo ndd -set /dev/tcp tcp_cwnd_max 16777216
sudo ndd -set /dev/tcp tcp_xmit_hiwat 4194304
sudo ndd -set /dev/tcp tcp_recv_hiwat 16777216
sudo ndd -set /dev/tcp tcp_keepalive_interval 300000

But I don't understand why setting it via /etc/system doesn't work. I created a script to run at each login since the settings are not persist across boots anyway.

#2

Updated by Dan McDonald 3 months ago

In native zones, each of these tunables has the supported interface of ipadm(1M). ipadm(1M) maintains each netstack's tunables. Each zone has its own TCP/IP "netstack".

/etc/system is for system-wide tunables, which these are note.

The LX branded zone has issues with ipadm(1M)-maintenance, but it is not an upstream illumos bug.

Likewise, it's not clear what is printing this "too large MTU". If it is an LX zone, that issue does not belong here, it belongs in the distro you're using (SmartOS?).

#3

Updated by gh origin 3 months ago

Dan McDonald wrote:

In native zones, each of these tunables has the supported interface of ipadm(1M). ipadm(1M) maintains each netstack's tunables. Each zone has its own TCP/IP "netstack".

/etc/system is for system-wide tunables, which these are note.

The LX branded zone has issues with ipadm(1M)-maintenance, but it is not an upstream illumos bug.

Likewise, it's not clear what is printing this "too large MTU". If it is an LX zone, that issue does not belong here, it belongs in the distro you're using (SmartOS?).

This MTU too large is my own hardware problem. NetBSD also has trouble setting the correct MTU and OpenBSD set the MTU to 1728 by default. Linux and FreeBSD set the MTU to the normal value 1500, so does Illumos. But Linux and FreeBSD don't print out any MTU too large warning as Illumos and NetBSD.

I found these tunables on a website of an old Solaris 10 sysadmin (he switched to Linux later then). So his code is all using ndd but no ipadm.

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