On Sun, Sep 13, 2020 at 10:26 PM Krzysztof Hałasa <khal...@piap.pl> wrote: > > Xie He <xie.he.0...@gmail.com> writes: > > > The HDLC device is not actually prepending any header when it is used > > with this driver. When the PVC device has prepended its header and > > handed over the skb to the HDLC device, the HDLC device just hands it > > over to the hardware driver for transmission without prepending any > > header. > > That's correct. IIRC: > - Cisco and PPP modes add 4 bytes > - Frame Relay adds 4 (specific protocols - mostly IPv4) or 10 (general > case) bytes. There is that pvcX->hdlcX transition which adds nothing > (the header is already in place when the packet leaves pvcX device). > - Raw mode adds nothing (IPv4 only, though it could be modified for > both IPv4/v6 easily) > - Ethernet (hdlc_raw_eth.c) adds normal Ethernet header.
Thank you for the nice summary! I just realized that we can indeed support both IPv4/v6 in hdlc_raw. Both IPv4 and v6 packets have a version field in the header, so we can use it to distinguish v4 and v6 packets on receiving. We can introduce it as a new feature some time.
