Very often when troubleshooting networking issues in an OVN cluster one
would like to know if any packet (or a specific one) is being dropped by
OVN.
Currently, this cannot be known because of two main reasons:
1 - Implicit drops: Some tables do not have a default action
(priority=0, match=1). In this case, a packet that does not match any
rule will be silently dropped.
2 - Even on explicit drops, we only know a packet was dropped. We lack
information about that packet.
In order to improve this, this series introduces a two-fold solution:
- First, make all drops explicit:
- northd add a default (match = "1") "drop;" action to those tables
that currently lack one.
- ovn-controller add an explicit drop action on those tables are not
associated with logical flows (i.e: physical-to-logical mappings).
- Secondly, allow sampling of all drops. By introducing a new OVN
action: "sample" (equivalent to OVS's), OVN can make OVS sample the
packets as they are dropped. In order to be able to correlate those
samples back to what exact rule generated them, the user specifies the
a 8-bit observation_domain_id. Based on that, the samples contain
the following fields:
- obs_domain_id:
- 8 most significant bits = the provided observation_domain_id.
- 24 least significant bits = the datapath's tunnely key if the
drop comes from a lflow or zero otherwise.
- obs_point_id: the first 32-bits of the lflow's UUID (i.e: the
cookie) if the drop comes from an lflow or the table number
otherwise.
Based on the above changes in the flows, all of which are optional,
users can collect IPFIX samples of the packets that are dropped by OVN
which contain header information useful for debugging.
* Note on observation_domain_ids:
By allowing the user to specify only the 8 most significant bits of the
obs_domain_id and having OVN combine it with the datapath's tunnel key,
OVN could be extended to support more than one "sampling" application.
For instance, ACL sampling could be developed in the future and, by
specifying a different observation_domain_id, it could co-exist with the
drop sampling mode implemented in the current series while still
allowing to uniquely identify the flow that created the sample.
* Notes on testing and usage:
Any IPFIX collector that parses ObservationPointID and
ObservationDomainID fields can be used. For instance, nfdump 1.7
supports these fields in nfdump. Example of how to capture and analyze
drops:
# Enable debug sampling:
$ ovn-nbctl set NB_Global . options:debug_drop_collector_set=1
options:debug_drop_domain_id=1
# Start nfcapd:
nfcapd -p 2055 -l nfcap &
# Configue sampling on the OVS you want to inspect:
$ ovs-vsctl --id=@br get Bridge br-int -- --id=@i create IPFIX
targets=\"172.18.0.1:2055\" -- create Flow_Sample_Collector_Set
bridge=@br id=1
# Inspect samples and figure out what LogicalFlow caused them:
$ nfdump -r nfcap -o fmt:'%line %odid %opid'
Date first seen Duration Proto Src IP Addr:Port
Dst IP Addr:Port Packets Bytes Flows obsDomainID obsPointID
1970-01-01 01:09:36.000 00:00:00.000 UDP 172.18.0.1:49230 ->
239.255.255.250:1900 12 6356 1 0x001000009 0x00d8dd23c7
1970-01-01 01:01:34.000 00:00:00.000 UDP 172.18.0.1:5353 ->
224.0.0.251:5353 165 89257 1 0x001000009 0x00d8dd23c7
[...]
$ ovn-sb vn-sbctl list Logical_Flow | grep -A 11 d8dd23c7
_uuid : d8dd23c7-1451-4ea3-add7-8d68b4be4691
actions :
"sample(probability=65535,collector_set=1,obs_domain=1,obs_point=$cookie);
/* drop */"
controller_meter : []
external_ids : {source="northd.c:12504",
stage-name=lr_in_ip_input}
logical_datapath : []
logical_dp_group : 0dc1b195-c647-4277-aea0-0bad5e896f51
match : "ip4.mcast || ip6.mcast"
pipeline : ingress
priority : 82
table_id : 3
tags : {}
hash : 0
V4 -> V5: Added documentation
V3 -> V4: Make explicit drops the default behavior.
V2 -> V3: Fix rebase problem on unit test
V1 -> V2
- Rebased and Addressed Mark's comments.
- Added NEWS section.
Adrian Moreno (3):
actions: add sample action
northd: make default drops explicit
northd: add drop sampling
NEWS | 2 +
controller/lflow.c | 1 +
controller/ovn-controller.c | 44 ++++++
controller/physical.c | 77 ++++++++-
controller/physical.h | 6 +
include/ovn/actions.h | 16 ++
lib/actions.c | 120 ++++++++++++++
northd/automake.mk | 2 +
northd/debug.c | 98 ++++++++++++
northd/debug.h | 30 ++++
northd/northd.c | 109 ++++++++-----
northd/ovn-northd.8.xml | 66 +++++++-
ovn-nb.xml | 28 ++++
ovn-sb.xml | 81 ++++++++++
tests/ovn-northd.at | 84 ++++++++++
tests/ovn.at | 303 ++++++++++++++++++++++++++++++++----
tests/test-ovn.c | 3 +
utilities/ovn-trace.c | 2 +
18 files changed, 996 insertions(+), 76 deletions(-)
create mode 100644 northd/debug.c
create mode 100644 northd/debug.h
--
2.37.3
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