Re: Request DLT_/LINKTYPE_ value for vSockets

[Guy Harris <guy () alum mit edu>]

On Jul 19, 2016, at 7:12 AM, Gerard Garcia <ggarcia () abra uab cat> wrote:

> >      2) What is the format of the transport header?
>
> It is well described in the virtio vsock specification: https://stefanha.github.io/virtio/#x1-2800007 May we just 
> link there?

If that's

struct virtio_vsock_hdr { 
  le64 src_cid; 
  le64 dst_cid; 
  le32 src_port; 
  le32 dst_port; 
  le32 len; 
  le16 type; 
  le16 op; 
  le32 flags; 
  le32 buf_alloc; 
  le32 fwd_cnt; 
};

that appears to duplicate fields in the link-layer header; are those fields, in fact, duplicates?

> >      3) Will the length of the transport header ever change?
>
> We should assume that it may change.

So will the transport header ever change *without* the length changing?  If it changes by adding new data to the end, 
or by removing some fields at the end, code that parses a packet in a capture can use the length field to determine 
whether the added fields are present, but if the header can change without the length changing - or by more than just 
fields being added to the end or removed from the end - there needs to be something in the header to give a version for 
the transport header, such as changing the transport header type.
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