To support tagged MPLS or QinQ traffic, it is necessary to change the MTU.
For QinQ, an MTU of 1508 is sufficient, while for MPLS, the MTU depends on the depth of the label stack.
Additionally, some implementations of the ISIS protocol use more MTU than specified in the network equipment settings.

DPI provides the ability to increase the MTU to 1518 without changing other settings.
Settings depend on the cards used.

In the configuration file fastdpi.conf set the parameter snaplen=<mtu_size>

1. In the configuration file fastdpi.conf set the parameter snaplen=<mtu_size>
2. Set on the network interfaces:

   ifconfig: sudo ifconfig eth0 mtu 1500

   or

   nmcli: sudo nmcli connection modify team1-port1 802-3-ethernet.mtu 9000

   or

   /etc/sysconfig/network-scripts/ifcfg-if1
    
   TYPE=Ethernet
   MTU=4096
   PROXY_METHOD=none
   BROWSER_ONLY=no
   IPV6INIT=no
   IPV6_DEFROUTE=yes
   IPV6_FAILURE_FATAL=no
   IPV6_ADDR_GEN_MODE=default
   NAME="if1"
   UUID=53b84dd0-3c5e-3397-b764-7ad40f1ad14c
   DEVICE=enp129s0f0np0
   ONBOOT=yes
   AUTOCONNECT_PRIORITY=-999
   IPV6_DISABLED=yes

nmcli con show

A significant MTU change may lead to decreased performance and may require changes to other driver settings and internal DPI service settings.
If a more significant MTU change is necessary, consult with technical support.