KK,
I read that you'll discard this packet, but I don't think we should do
so. The correct behavior would be to install flow table with nw_proto=6,
tp_src=0 and tp_dst=0, and does pkt_out (i.e. forward it). I agree this
packet looks strange (tcp_header length=0), but L2/L3 switch/router will
forward this (otherwise we won't see this packet).
Masa
On 01/13/2011 06:28 PM, Masayoshi Kobayashi wrote:
KK,
> I thought about it a little. Why is the switch doing step 7?
Because the action of pkt_out is "OFPP_TABLE".
(the packet in pkt_out does not match to the entry that is installed by
flow_mod, since the matching entry says nw_proto=0).
Masa
On 01/13/2011 06:06 PM, kk yap wrote:
Hi Srini,
I thought about it a little. Why is the switch doing step 7?
Anyway, I do agree that NOX is not handling malformed packets right.
I have included an invalid field in the struct flow, and created a
component that ignore invalid packets. If anyone will double-check
and test the patches attached, I will push it.
Regards
KK
On 13 January 2011 16:13, Srini Seetharaman<seeth...@stanford.edu> wrote:
I explained this to KK in person. For others, here is the sequence of
events:
1. Packet arrives with (nw_proto=6, tp_src=0, tp_dst=0). Store in
bufid 'X'
2. flow.cc identifies that the arrived TCP packet is corrupted, and
generates
pkt_in event with flow structure having (nw_proto=0, tp_src=0, tp_dst=0)
3. Authenticator generates a flow_in with flow_in.flow being same as
above
3. routing.cc generates a flow_mod for the flow_in with the match
pattern
defined using the fields of the flow_in.flow
4. Switch inserts a flow table entry for matching (nw_proto=0,
tp_src=0, tp_dst=0)
5. routing.cc generates a pkt_out for the bufid 'X' with action =
OFPP_TABLE
6. Switch notices that the packet in bufid 'X' has no matching flow
table entry,
because there is a mismatch on the nw_proto field
7. Switch generates a new pkt_in event
8. Go to step (2)
This is the infinite loop.
Srini.
On Thu, Jan 13, 2011 at 1:08 PM, kk yap<yap...@stanford.edu> wrote:
Hi Srini,
I think you are fixing this in the wrong place. Putting nw_proto=0
does not cause an infinite loop. Where is the loop happening? Can
you provide more detailed NOX output so that we can even start looking
at this.
Regards
KK
On 13 January 2011 11:02, Srini Seetharaman<seeth...@stanford.edu>
wrote:
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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--
Masayoshi Kobayashi
Visiting Scholar at Stanford University
System Platform Research Labs, NEC Corporation.
T/M: 650-714-3154
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