[ovs-discuss] OpenVSwitch - Error packet OFPFMFC_BAD_COMMAND of code ofp_flow_mod_failed_code coming as malformed.

[Ben Pfaff]

Can you show me this malformed error packet, and tell me in what way
it is malformed?

On Tue, May 22, 2012 at 09:50:20AM +0000, Prabina Pattnaik wrote:
> Hi Ben,
> 
> We agree that implementation of 'at least 64 bytes' is as per spec (to allow data above 64 bytes depends on vendor specific switch implementation).
> But in current implementation, when the code (mentioned below) limits the size of data to 64 bytes (if data field of the error packet is more than 64 bytes), a malformed OFPFMFC_BAD_COMMAND error packets gets generated (visible on wireshark with openflow plugin).
> 
> As per our analysis, removal of code to limit the data size to 64, resolves the issue of malformed packet.
> 
> File: lib/ofputil.c 
> Routine ofputil_encode_error_msg
> 
> If (oh){
>     Xid = oh->xid;
>     data = oh;
>     len = ntohs(oh->length);
>    - if (len > 64){
>    -   len =64;
>    - }
>   }
> 
>  
> Regards,
> Prabina
> 
> 
> -----Original Message-----
> From: Ben Pfaff [mailto:blp at nicira.com] 
> Sent: Monday, May 21, 2012 10:24 PM
> To: Prabina Pattnaik
> Cc: bugs at openvswitch.org
> Subject: Re: [ovs-discuss] OpenVSwitch - Error packet OFPFMFC_BAD_COMMAND of code ofp_flow_mod_failed_code coming as malformed.
> 
> On Mon, May 21, 2012 at 11:15:28AM +0000, Prabina Pattnaik wrote:
> > As per openflow 1.0 spec "data" contains at "least" first 64 bytes
> > of failed request. This is working correct also in current OVS 1.2.2
> > code.
> >
> > But it is taking an extra check in code (lib/ofp-util.c) on "data"
> > length that:-
> >
> > if data is greater than 64 bytes then it would be truncated to 64
> > bytes which is making this packet as malformed. OVS code is working
> > on "at most" 64 bytes length instead of "at least" 64 bytes.
> > 
> > To avoid the truncation of 'data field ' to 64 bytes, the condition
> > to check the length of data field in file (lib/ofp-util.c), routine
> > ofputil_encode_error_msg can be removed.
> 
> I disagree with your interpretation.  "At least" 64 bytes means that
> OVS is allowed to truncate the inner message after 64 bytes.  That is
> what it is doing.
> 
> 
> 
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