Extremely low throughput between AIX 7.2 and RHEL Maipo Post: 303044541

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Operating Systems Linux Red Hat Extremely low throughput between AIX 7.2 and RHEL Maipo Post 303044541 by Neo on Wednesday 26th of February 2020 12:13:40 AM

02-26-2020

Administrator

Quote:

Originally Posted by MadeInGermany

I wonder why the shown MTU is 1460 while the standard is 1500.
But if your LAN switch/router works better with 1460 then try to set it on the other box, too.

I remember a similar issue (severe packet loss), where all Linux systems had the standard MTU 1500. The LAN guy changed the MTU on the LAN switch (or router?), and that fixed it.

Google Cloud mandates this MTU:

Quote:

Gateway MTU vs. system MTU

You must configure your peer VPN gateway to use a MTU of no greater than 1460 bytes. A value of 1460 bytes is recommended because that matches the default MTU setting for Google Cloud VM instances.

The effective MTU for peer systems and Google Cloud VMs is typically lower than the MTU of your VPN gateway:

For TCP traffic, MSS clamping rewrites the SYN packet of the initial TCP handshake. This allows systems to dynamically adjust Maximum Segment Size (MSS) to accommodate encapsulation.

For UDP traffic, Path MTU Discovery (PMTUD) can negotiate smaller MTU sizes, under certain circumstances, provided that your firewall permits ICMP traffic.

REF: MTU considerations | Cloud VPN | Google Cloud

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LEARN ABOUT OPENSOLARIS

synos

synos(1)                                                        Mail Avenger 0.8.3                                                        synos(1)

NAME

       synos - guess operating system from TCP SYN fingerprint

SYNOPSIS

       synos [--mtu mtu] [--db path] syn-fingerprint

DESCRIPTION

       synos takes a SYN fingerprint, in the format described for the CLIENT_SYNFP environment variable in the avenger(1) man page, and outputs a
       guess as to the type of the client operating system.  synos makes use of the OpenBSD SYN fingerprint database (which is also repackaged
       with Mail Avenger).

   OPTIONS
       --mtu val
           Certain operating systems set the initial TCP window size based on the maximum transmission unit, or MTU, of the network.  For such
           operating systems, synos usually checks the window size using both the client's MSS option plus 40 bytes (for TCP and IP headers), or a
           hard-coded MTU, which defaults to 1,500 bytes.  If either value works, the fingerprint is considered to match the operating system.
           You can change the value 1,500 by specifying this option.  A value of 0 tells synos to use only the value derived from the MSS option.

       --db file
           Specifies an alternate location for the SYN fingerprint database.

FILES

       /usr/local/share/pf.os
           Default location of SYN fingerprint database.

SEE ALSO

       avenger(1), asmtpd(8)

       The Mail Avenger home page: <http://www.mailavenger.org/>.

       The OpenBSD home page: <http://www.openbsd.org/>.

BUGS

       The operating system type is determined by heuristics that are not always reliable.  Moreover, not all operating systems can be
       distinguished.  The database may not even contain a client's particular operating system and version.

       It is not hard to fool synos deliberately by changing TCP socket options or injecting raw packets onto the network.

AUTHOR

       David Mazieres

Mail Avenger 0.8.3                                                  2012-04-05                                                            synos(1)