Hello Jan, 2018-10-29 17:40 GMT+01:00 Jan Just Keijser <[email protected]>:
> your assumption is that in TAP mode, OpenVPN would allow only Ethernet 802 > II traffic. For these type of packets, an extra 14 bytes would suffice. > However, for a full blown Ethernet virtual Ethernet adapter you need to > allocate some extra space for other frame types. This is why OpenVPN uses a > (fairly arbitrary) value of 32 bytes for Ethernet (tap) packets , compared > to 'tun' packets. This is controlled using the --tun-mtu-extra flag, which > is set to 0 for tun and to 32 for tap. You can test this yourself by setting > tun-mtu-extra 14 > on both sides in tap mode and then see if your connection still works; If > you set it to anything lower than 14, the link will fail. It *will* mean > that you can only send Ethernet/IP traffic of a tap link. > Thank you, that does indeed explain what I've been seeing. :) I'll also keep that in mind in case we wish to handle VLANs or MPLS headers. Kind regards, Pieter Hulshoff
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