From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Richardson Date: Tue, 08 Dec 2015 22:12:05 +0000 Subject: Re: MTU strategies Message-Id: <1708.1449612725@dooku.sandelman.ca> List-Id: References: <5665C351.3020500@seiner.com> In-Reply-To: <5665C351.3020500@seiner.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ppp@vger.kernel.org Yan Seiner wrote: > 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? If the VPN won't be involved, then 1492 is the best bet. PMTU is *supposed* to take care of all of this, but... > 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.