MTU strategies
I have a question on MTU size strategies.
I have a router that terminates a VPN. The router connects via ppp to my ISP. I have a physical interface, with a virtual interface for pppoe, and a tun interface for the VPN that runs over the pppoe interface.
The physical interface (eth0) has a MTU of 1500.
The pppoe interface has an MTU of 1492.
The vpn interface has an MTU of 1452, a figure I picked somewhat arbitrarily, assuming a 40 byte overhead for the vpn.
My question is then for the other interfaces on the router that face the LAN and the DMZ. Should these be set to 1492 or 1500?
And my other question is for the DHCP clients. Should they be set to 1492 (and the one host that uses the VPN should be set to 1452)?
root@AP1:~# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:0D:B9:35:C2:0C
inet6 addr: fe80::20d:b9ff:fe35:c20c/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:184584 errors:0 dropped:0 overruns:0 frame:0
TX packets:117581 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:208509762 (198.8 MiB) TX bytes:16719097 (15.9 MiB)root@AP1:~# ifconfig pppoe-wan
pppoe-wan Link encap:Point-to-Point Protocol
inet addr:198.251.62.82 P-t-P:198.251.52.2 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1492 Metric:1
RX packets:182822 errors:0 dropped:0 overruns:0 frame:0
TX packets:114465 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:3
RX bytes:204567089 (195.0 MiB) TX bytes:14019020 (13.3 MiB)root@AP1:~# ifconfig tun0
tun0 Link encap:UNSPEC HWaddr
00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
inet addr:10.117.1.6 P-t-P:10.117.1.5 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1452 Metric:1
RX packets:289 errors:0 dropped:0 overruns:0 frame:0
TX packets:407 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:39746 (38.8 KiB) TX bytes:76331 (74.5 KiB)Quoted 9 lines · Yan Seiner
I have a question on MTU size strategies.
I have a router that terminates a VPN. The router connects via ppp to my ISP. I have a physical interface, with a virtual interface for pppoe, and a tun interface for the VPN that runs over the pppoe interface.
The physical interface (eth0) has a MTU of 1500.
Quoted 7 lines
The pppoe interface has an MTU of 1492.
The vpn interface has an MTU of 1452, a figure I picked somewhat arbitrarily, assuming a 40 byte overhead for the vpn.
My question is then for the other interfaces on the router that face the LAN and the DMZ. Should these be set to 1492 or 1500?
If the VPN won't be involved, then 1492 is the best bet. PMTU is *supposed* to take care of all of this, but...
Quoted 2 lines
And my other question is for the DHCP clients. Should they be set to 1492 (and the one host that uses the VPN should be set to 1452)?
The DHCP client should receive 1492 from the server, and set it on the interface.