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:b...@nicira.com]
Sent: Monday, May 21, 2012 10:24 PM
To: Prabina Pattnaik
Cc: b...@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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