Recommendations

Enable forwarding

To enable packet forwarding need edit /etc/sysctl.conf and add or uncomment next:

net.ipv4.ip_forward=1
net.ipv6.conf.all.forwarding=1

For apply this params now, use command sysctl -p or after reboot server this params will be applied automatically.

MTU

If used vlan-per-user often required 802.1ad standard also called as QinQ or Q-in-Q, then need to set MTU on main interface and S-VLAN, because adding to headed one more field. Interface which using QinQ usualy consist of <interface_name>.<S-VLAN>.<C-VLAN>. S-VLAN (Service VLAN) is TAG which wrap C-VLAN (Customer VLAN).

As example:

MTU
           1514
             |   1514
             |   |   1500
             |   |   |
          eth0.2001.101
             |   |   |
             |   |   C-VLAN
             |   S-VLAN
             Interface

Set up MTU on interface eth0 and interface with S-VLAN

ip link set eth0 mtu 1514
ip link set eth0.2001 mtu 1514

Note:

If used bonding need change MTU on bonding (bond0) and slaves (eth0, eth1 …) interfaces.

Increase ARP cache size

If accel-ppp used as DHCP BRAS important to increase ARP cache size, otherwise you can cache overflow and clients have lost connections. Edit /etc/sysctl.conf and add next:

net.ipv4.neigh.default.gc_thresh1 = 4096
net.ipv4.neigh.default.gc_thresh2 = 8192
net.ipv4.neigh.default.gc_thresh3 = 12288
net.ipv6.neigh.default.gc_thresh1 = 4096
net.ipv6.neigh.default.gc_thresh2 = 8192
net.ipv6.neigh.default.gc_thresh3 = 12288

For apply this params now, use command sysctl -p or after reboot server this params will be applied automatically.