On 2015-07-31 00:15, Martin Blumenstingl wrote: > On Wed, Jul 29, 2015 at 8:05 AM, Willem de Bruijn <will...@google.com> wrote: >> Martin, to return to your initial statement that PPPoE PADI packets can >> have a zero payload: the PPPoE RFC states that PADI packets "MUST >> contain exactly one TAG of TAG_TYPE Service-Name, indicating the >> service the Host is requesting, and any number of other TAG types." >> (RFC 2516, 5.1). Is the observed behavior (no payload) perhaps >> incorrect? > As far as I can see you are right, but the real world seems to be different. > My ISP for example lists the PPPoE connection settings, but they are > nowhere mentioning the "service name". > > I have also re-read pppd's source code again and that seems to confirm > what you are reading in the RFC: Leaving the service name away makes > seems to violate the RFC, but pppd still accepts those configurations. > >> Even if it is, if this is breaking established userspace expectations, >> we should look into it. Ethernet specifies a minimum payload size of >> 46 on the wire, but perhaps that is handled with padding, so that >> 0 length should be valid within the stack. Also, there may be other >> valid uses of 0 length payload on top of link layers that are not Ethernet. > Good catch. I would also like to note that the documentation for > "hard_header_len" describes it as "Hardware header length". When the > purpose of this field we should check whether the documentation should > be updated to "Minimum hardware header length" -> that would mean the > condition has to be a "len < hard_header_len" instead of a "len <= > hard_header_len" (as it is now). > > PS: I have also added the pppd maintainer (Paul Mackerras) to this > thread because I think he should know about this issue (and he can > probably provide more details if required). > As a quick summary for him: linux >= 3.19 rejects PADI packets when > no service name is configured. Any news on this? Users are complaining about this regression: https://dev.openwrt.org/ticket/20707
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