R3--R1--Internet--R90
R3: ip addr 10.123.0.3
R1:
sudo ip l2tp add tunnel tunnel_id 699 peer_tunnel_id 699 encap udp local 5.254.174.8
remote 5.254.174.90 udp_sport 699 udp_dport 699
sudo ip l2tp add session tunnel_id 699 session_id 699 peer_session_id 699
sudo ip link set l2tpeth0 up mtu 1446
sudo ip link add brvlan699 type bridge
sudo ip link set l2tpeth0 master brvlan699
sudo vconfig add eth1 699
sudo ip link set eth1.699 master brvlan699
sudo ip link set brvlan699 up
sudo ip a add 10.123.0.1/24 dev brvlan699
R90:
ip l2tp add tunnel tunnel_id 699 peer_tunnel_id 699 encap udp local 5.254.174.90 remote 5.254.174.8 udp_sport 699 udp_dport 699
ip l2tp add session tunnel_id 699 session_id 699 peer_session_id 699
ip link set l2tpeth0 up mtu 1446
ip link add brvlan699 type bridge
ip link set l2tpeth0 master brvlan699
vconfig add eth1 699
ip link set eth1.699 master brvlan699
ip link set brvlan699 up
ip a add 10.123.0.90/24 dev brvlan699
So we have R1 10.123.0.1, R90 10.123.0.90, R3 10.123.0.3
every host can ping every. But R3->R90 or R90->R3 can ping only max ICMP packet size 1446 as mtu l2tpeth0 interface.
Why it dont fragment and send more packets? R1 can send even 15 000B ICMP to R3 or R90 through tunnel, but ping end-to-end through R1 only 1446, more is timeout. How to optimalise mtu and mss values for this tunnel with inside vlan and how to make it work for bigger packets with fragmentation?