We don't know who sent it, but it came from outside our network. If it
is easy to take down a network by just sending 1 invalid packet, I'd
be worried!
On Thu, Jan 13, 2011 at 10:59 AM, kk yap <yap...@stanford.edu> wrote:
> Hi Srini,
>
> What is this packet? The length of TCP is zero?!?! I wish to
> understand the circumstance for which we are getting the packet before
> commenting on the right way to handle this.
>
> Regards
> KK
>
>
> On 13 January 2011 10:38, Srini Seetharaman <seeth...@stanford.edu> wrote:
>> When someone sends the attached packet to a switch, it generates an
>> infinite loop of packet_ins in our production network. This is because
>> this incoming tcp packet has nw_proto=6 and tcp port numbers of "0",
>> but outgoing flow_mod has nw_proto of "0" and tcp port numbers of "0".
>> So, the packet_out generates a new packet_in and this loop continues
>> forever.
>>
>> I see the following code in src/lib/flow.cc (both in NOX-Zaku and
>> SNAC). I believe this is what is causing the nw_proto to be "0" in the
>> flow_mod. I'm not sure who wrote that piece of code. This is not
>> handling corrupted packets well and rejecting this packet as a invalid
>> TCP packet. Does anyone see problems with removing the "else" clause?
>>
>> if (nw_proto == ip_::proto::TCP) {
>> const tcp_header *tcp = pull_tcp(b);
>> if (tcp) {
>> tp_src = tcp->tcp_src;
>> tp_dst = tcp->tcp_dst;
>> } else {
>> /* Avoid tricking other code into thinking that
>> * this packet has an L4 header. */
>> nw_proto = 0;
>> }
>> }
>>
>> FYI, pull_tcp is defined as below:
>> static const tcp_header * pull_tcp(Buffer& b)
>> {
>> if (const tcp_header *tcp = b.try_at<tcp_header>(0)) {
>> int tcp_len = TCP_OFFSET(tcp->tcp_ctl) * 4;
>> if (tcp_len >= sizeof *tcp) {
>> return reinterpret_cast<const
>> tcp_header*>(b.try_pull(tcp_len));
>> }
>> }
>> return 0;
>> }
>>
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>>
>>
>
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