Provided by: ovn-common_24.03.2-0ubuntu0.24.04.1_amd64 
NAME
ovn-trace - Open Virtual Network logical network tracing utility
SYNOPSIS
ovn-trace [options] [datapath] microflow
ovn-trace [options] --detach
DESCRIPTION
This utility simulates packet forwarding within an OVN logical network. It can be used to
run through ``what-if’’ scenarios: if a packet originates at a logical port, what will
happen to it and where will it ultimately end up? Users already familiar with the Open
vSwitch ofproto/trace command described in ovs-vswitch(8) will find ovn-trace to be a
similar tool for logical networks.
ovn-trace works by reading the Logical_Flow and other tables from the OVN southbound
database (see ovn-sb(5)). It simulates a packet’s path through logical networks by
repeatedly looking it up in the logical flow table, following the entire tree of
possibilities.
ovn-trace simulates only the OVN logical network. It does not simulate the physical
elements on which the logical network is layered. This means that, for example, it is
unimportant how VMs are distributed among hypervisors, or whether their hypervisors are
functioning and reachable, so ovn-trace will yield the same results regardless. There is
one important exception: ovn-northd, the daemon that generates the logical flows that
ovn-trace simulates, treats logical ports differently based on whether they are up or
down. Thus, if you see surprising results, ensure that the ports involved in a simulation
are up.
The simplest way to use ovn-trace is to provide the microflow (and optional datapath)
arguments on the command line. In this case, it simulates the behavior of a single packet
and exits. For an alternate usage model, see Daemon Mode below.
The optional datapath argument specifies the name of a logical datapath. Acceptable names
are the name from the northbound Logical_Switch or Logical_Router table, the UUID of a
record from one of those tables, or the UUID of a record from the southbound
Datapath_Binding table. (The datapath is optional because ovn-trace can figure it out from
the inport that the microflow matches.)
The microflow argument describes the packet whose forwarding is to be simulated, in the
syntax of an OVN logical expression, as described in ovn-sb(5), to express constraints.
The parser understands prerequisites; for example, if the expression refers to ip4.src,
there is no need to explicitly state ip4 or eth.type == 0x800.
For reasonable L2 behavior, the microflow should include at least inport and eth.dst, plus
eth.src if port security is enabled. For example:
inport == "lp11" && eth.src == 00:01:02:03:04:05 && eth.dst == ff:ff:ff:ff:ff:ff
For reasonable L3 behavior, microflow should also include ip4.src and ip4.dst (or ip6.src
and ip6.dst) and ip.ttl. For example:
inport == "lp111" && eth.src == f0:00:00:00:01:11 && eth.dst == 00:00:00:00:ff:11
&& ip4.src == 192.168.11.1 && ip4.dst == 192.168.22.2 && ip.ttl == 64
Here’s an ARP microflow example:
inport == "lp123"
&& eth.dst == ff:ff:ff:ff:ff:ff && eth.src == f0:00:00:00:01:11
&& arp.op == 1 && arp.sha == f0:00:00:00:01:11 && arp.spa == 192.168.1.11
&& arp.tha == ff:ff:ff:ff:ff:ff && arp.tpa == 192.168.2.22
ovn-trace will reject erroneous microflow expressions, which beyond syntax errors fall
into two categories. First, they can be ambiguous. For example, tcp.src == 80 is ambiguous
because it does not state IPv4 or IPv6 as the Ethernet type. ip4 && tcp.src > 1024 is also
ambiguous because it does not constrain bits of tcp.src to particular values. Second, they
can be contradictory, e.g. ip4 && ip6.
OUTPUT
ovn-trace supports the three different forms of output, each described in a separate
section below. Regardless of the selected output format, ovn-trace starts the output with
a line that shows the microflow being traced in OpenFlow syntax.
Detailed Output
The detailed form of output is also the default form. This form groups output into
sections headed up by the ingress or egress pipeline being traversed. Each pipeline lists
each table that was visited (by number and name), the ovn-northd source file and line
number of the code that added the flow, the match expression and priority of the logical
flow that was matched, and the actions that were executed.
The execution of OVN logical actions naturally forms a ``control stack’’ that resembles
that of a program in conventional programming languages such as C or Java. Because the
next action that calls into another logical flow table for a lookup is a recursive
construct, OVN ``programs’’ in practice tend to form deep control stacks that, displayed
in the obvious way using additional indentation for each level, quickly use up the
horizontal space on all but the widest displays. To make detailed output more readable,
without loss of generality, ovn-trace omits indentation for ``tail recursion,’’ that is,
when next is the last action in a logical flow, it does not indent details of the next
table lookup more deeply. Output still uses indentation when it is needed for clarity.
OVN ``programs’’ traces also tend to encounter long strings of logical flows with match
expression 1 (which matches every packet) and the single action next;. These are
uninteresting and merely clutter output, so ovn-trace omits them entirely even from
detailed output.
The following excerpt from detailed ovn-trace output shows a section for a packet
traversing the ingress pipeline of logical datapath ls1 with ingress logical port lp111.
The packet matches a logical flow in table 0 (aka ls_in_port_sec_l2) with priority 50 and
executes next(1); to pass to table 1. Tables 1 through 11 are trivial and omitted. In
table 19 (aka ls_in_l2_lkup), the packet matches a flow with priority 50 based on its
Ethernet destination address and the flow’s actions output the packet to the
lrp11-attachement logical port.
ingress(dp="ls1", inport="lp111")
---------------------------------
0. ls_in_port_sec_l2: inport == "lp111", priority 50
next(1);
19. ls_in_l2_lkup: eth.dst == 00:00:00:00:ff:11, priority 50
outport = "lrp11-attachment";
output;
Summary Output
Summary output includes the logical pipelines visited by a packet and the logical actions
executed on it. Compared to the detailed output, however, it removes details of tables and
logical flows traversed by a packet. It uses a format closer to that of a programming
language and does not attempt to avoid indentation. The summary output equivalent to the
above detailed output fragment is:
ingress(dp="ls1", inport="lp111") {
outport = "lrp11-attachment";
output;
...
};
Minimal Output
Minimal output includes only actions that modify packet data (not including OVN registers
or metadata such as outport) and output actions that actually deliver a packet to a
logical port (excluding patch ports). The operands of actions that modify packet data are
displayed reduced to constants, e.g. ip4.dst = reg0; might be show as ip4.dst =
192.168.0.1; if that was the value actually loaded. This yields output even simpler than
the summary format. (Users familiar with Open vSwitch may recognize this as similar in
spirit to the datapath actions listed at the bottom of ofproto/trace output.)
The minimal output format reflects the externally seen behavior of the logical networks
more than it does the implementation. This makes this output format the most suitable for
use in regression tests, because it is least likely to change when logical flow tables are
rearranged without semantic change.
STATEFUL ACTIONS
Some OVN logical actions use or update state that is not available in the southbound
database. ovn-trace handles these actions as described below:
ct_next
By default ovn-trace treats flows as ``tracked’’ and ``established.’’ See
the description of the --ct option for a way to override this behavior.
ct_dnat (without an argument)
Forks the pipeline. In one fork, advances to the next table as if next; were
executed. The packet is not changed, on the assumption that no NAT state was
available. In the other fork, the pipeline continues without change after
the ct_dnat action.
ct_snat (without an argument)
This action distinguishes between gateway routers and distributed routers. A
gateway router is defined as a logical datapath that contains an l3gateway
port; any other logical datapath is a distributed router. On a gateway
router, ct_snat; is treated as a no-op. On a distributed router, it is
treated the same way as ct_dnat;.
ct_dnat(ip)
ct_snat(ip)
Forks the pipeline. In one fork, sets ip4.dst (or ip4.src) to ip and ct.dnat
(or ct.snat) to 1 and advances to the next table as if next; were executed. In
the other fork, the pipeline continues without change after the ct_dnat (or
ct_snat) action.
ct_lb;
ct_lb(ip[:port]...);
Forks the pipeline. In one fork, sets ip4.dst (or ip6.dst) to one of the load-
balancer addresses and the destination port to its associated port, if any,
and sets ct.dnat to 1. With one or more arguments, gives preference to the
address specified on --lb-dst, if any; without arguments, uses the address and
port specified on --lb-dst. In the other fork, the pipeline continues without
change after the ct_lb action.
ct_commit
put_arp
put_nd
These actions are treated as no-ops.
DAEMON MODE
If ovn-trace is invoked with the --detach option (see Daemon Options, below), it runs in
the background as a daemon and accepts commands from ovs-appctl (or another JSON-RPC
client) indefinitely. The currently supported commands are described below.
trace [options] [datapath] microflow
Traces microflow through datapath and replies with the results of the trace.
Accepts the options described under Trace Options below.
exit Causes ovn-trace to gracefully terminate.
OPTIONS
Trace Options
--detailed
--summary
--minimal
These options control the form and level of detail in ovn-trace output. If more than
one of these options is specified, all of the selected forms are output, in the order
listed above, each headed by a banner line. If none of these options is given,
--detailed is the default. See Output, above, for a description of each kind of
output.
--all
Selects all three forms of output.
--ovs[=remote]
Makes ovn-trace attempt to obtain and display the OpenFlow flows that correspond to
each OVN logical flow. To do so, ovn-trace connects to remote (by default,
unix:/br-int.mgmt) over OpenFlow and retrieves the flows. If remote is specified, it
must be an active OpenFlow connection method described in ovsdb(7).
To make the best use of the output, it is important to understand the relationship
between logical flows and OpenFlow flows. ovn-architecture(7), under Architectural
Physical Life Cycle of a Packet, describes this relationship. Keep in mind the
following points:
• ovn-trace currently shows all the OpenFlow flows to which a logical flow
corresponds, even though an actual packet ordinarily matches only one of
these.
• Some logical flows can map to the Open vSwitch ``conjunctive match’’ extension
(see ovs-fields(7)). Currently ovn-trace cannot display the flows with
conjunction actions that effectively produce the conj_id match.
• Some logical flows may not be represented in the OpenFlow tables on a given
hypervisor, if they could not be used on that hypervisor.
• Some OpenFlow flows do not correspond to logical flows, such as OpenFlow flows
that map between physical and logical ports. These flows will never show up in
a trace.
• When ovn-trace omits uninteresting logical flows from output, it does not look
up the corresponding OpenFlow flows.
--ct=flags
This option sets the ct_state flags that a ct_next logical action will report. The
flags must be a comma- or space-separated list of the following connection tracking
flags:
• trk: Include to indicate connection tracking has taken place. (This bit is set
automatically even if not listed in flags.
• new: Include to indicate a new flow.
• est: Include to indicate an established flow.
• rel: Include to indicate a related flow.
• rpl: Include to indicate a reply flow.
• inv: Include to indicate a connection entry in a bad state.
• dnat: Include to indicate a packet whose destination IP address has been
changed.
• snat: Include to indicate a packet whose source IP address has been changed.
The ct_next action is used to implement the OVN distributed firewall. For testing,
useful flag combinations include:
• trk,new: A packet in a flow in either direction through a firewall that has
not yet been committed (with ct_commit).
• trk,est: A packet in an established flow going out through a firewall.
• trk,rpl: A packet coming in through a firewall in reply to an established
flow.
• trk,inv: An invalid packet in either direction.
A packet might pass through the connection tracker twice in one trip through OVN:
once following egress from a VM as it passes outward through a firewall, and once
preceding ingress to a second VM as it passes inward through a firewall. Use multiple
--ct options to specify the flags for multiple ct_next actions.
When --ct is unspecified, or when there are fewer --ct options than ct_next actions,
the flags default to trk,est.
--lb-dst=ip[:port]
Sets the IP from VIP pool to use as destination of the packet. --lb-dst is not
available in daemon mode.
--select-id=id
Specify the id to be selected by the select action. id must be one of the values
listed in the select action. Otherwise, a random id is selected from the list, as if
--select-id were not specified. --select-id is not available in daemon mode.
--friendly-names
--no-friendly-names
When cloud management systems such as OpenStack are layered on top of OVN, they often
use long, human-unfriendly names for ports and datapaths, for example, ones that
include entire UUIDs. They do usually include friendlier names, but the long, hard-
to-read names are the ones that appear in matches and actions. By default, or with
--friendly-names, ovn-trace substitutes these friendlier names for the long names in
its output. Use --no-friendly-names to disable this behavior; this option might be
useful, for example, if a program is going to parse ovn-trace output.
Daemon Options
--pidfile[=pidfile]
Causes a file (by default, program.pid) to be created indicating the PID of the
running process. If the pidfile argument is not specified, or if it does not begin
with /, then it is created in .
If --pidfile is not specified, no pidfile is created.
--overwrite-pidfile
By default, when --pidfile is specified and the specified pidfile already exists
and is locked by a running process, the daemon refuses to start. Specify
--overwrite-pidfile to cause it to instead overwrite the pidfile.
When --pidfile is not specified, this option has no effect.
--detach
Runs this program as a background process. The process forks, and in the child it
starts a new session, closes the standard file descriptors (which has the side
effect of disabling logging to the console), and changes its current directory to
the root (unless --no-chdir is specified). After the child completes its
initialization, the parent exits.
--monitor
Creates an additional process to monitor this program. If it dies due to a signal
that indicates a programming error (SIGABRT, SIGALRM, SIGBUS, SIGFPE, SIGILL,
SIGPIPE, SIGSEGV, SIGXCPU, or SIGXFSZ) then the monitor process starts a new copy
of it. If the daemon dies or exits for another reason, the monitor process exits.
This option is normally used with --detach, but it also functions without it.
--no-chdir
By default, when --detach is specified, the daemon changes its current working
directory to the root directory after it detaches. Otherwise, invoking the daemon
from a carelessly chosen directory would prevent the administrator from unmounting
the file system that holds that directory.
Specifying --no-chdir suppresses this behavior, preventing the daemon from changing
its current working directory. This may be useful for collecting core files, since
it is common behavior to write core dumps into the current working directory and
the root directory is not a good directory to use.
This option has no effect when --detach is not specified.
--no-self-confinement
By default this daemon will try to self-confine itself to work with files under
well-known directories determined at build time. It is better to stick with this
default behavior and not to use this flag unless some other Access Control is used
to confine daemon. Note that in contrast to other access control implementations
that are typically enforced from kernel-space (e.g. DAC or MAC), self-confinement
is imposed from the user-space daemon itself and hence should not be considered as
a full confinement strategy, but instead should be viewed as an additional layer of
security.
--user=user:group
Causes this program to run as a different user specified in user:group, thus
dropping most of the root privileges. Short forms user and :group are also allowed,
with current user or group assumed, respectively. Only daemons started by the root
user accepts this argument.
On Linux, daemons will be granted CAP_IPC_LOCK and CAP_NET_BIND_SERVICES before
dropping root privileges. Daemons that interact with a datapath, such as
ovs-vswitchd, will be granted three additional capabilities, namely CAP_NET_ADMIN,
CAP_NET_BROADCAST and CAP_NET_RAW. The capability change will apply even if the new
user is root.
On Windows, this option is not currently supported. For security reasons,
specifying this option will cause the daemon process not to start.
Logging Options
-v[spec]
--verbose=[spec]
Sets logging levels. Without any spec, sets the log level for every module and
destination to dbg. Otherwise, spec is a list of words separated by spaces or commas
or colons, up to one from each category below:
• A valid module name, as displayed by the vlog/list command on ovs-appctl(8),
limits the log level change to the specified module.
• syslog, console, or file, to limit the log level change to only to the system
log, to the console, or to a file, respectively. (If --detach is specified,
the daemon closes its standard file descriptors, so logging to the console
will have no effect.)
On Windows platform, syslog is accepted as a word and is only useful along
with the --syslog-target option (the word has no effect otherwise).
• off, emer, err, warn, info, or dbg, to control the log level. Messages of the
given severity or higher will be logged, and messages of lower severity will
be filtered out. off filters out all messages. See ovs-appctl(8) for a
definition of each log level.
Case is not significant within spec.
Regardless of the log levels set for file, logging to a file will not take place
unless --log-file is also specified (see below).
For compatibility with older versions of OVS, any is accepted as a word but has no
effect.
-v
--verbose
Sets the maximum logging verbosity level, equivalent to --verbose=dbg.
-vPATTERN:destination:pattern
--verbose=PATTERN:destination:pattern
Sets the log pattern for destination to pattern. Refer to ovs-appctl(8) for a
description of the valid syntax for pattern.
-vFACILITY:facility
--verbose=FACILITY:facility
Sets the RFC5424 facility of the log message. facility can be one of kern, user,
mail, daemon, auth, syslog, lpr, news, uucp, clock, ftp, ntp, audit, alert, clock2,
local0, local1, local2, local3, local4, local5, local6 or local7. If this option is
not specified, daemon is used as the default for the local system syslog and local0
is used while sending a message to the target provided via the --syslog-target
option.
--log-file[=file]
Enables logging to a file. If file is specified, then it is used as the exact name
for the log file. The default log file name used if file is omitted is
/var/log/ovn/program.log.
--syslog-target=host:port
Send syslog messages to UDP port on host, in addition to the system syslog. The host
must be a numerical IP address, not a hostname.
--syslog-method=method
Specify method as how syslog messages should be sent to syslog daemon. The following
forms are supported:
• libc, to use the libc syslog() function. Downside of using this options is
that libc adds fixed prefix to every message before it is actually sent to the
syslog daemon over /dev/log UNIX domain socket.
• unix:file, to use a UNIX domain socket directly. It is possible to specify
arbitrary message format with this option. However, rsyslogd 8.9 and older
versions use hard coded parser function anyway that limits UNIX domain socket
use. If you want to use arbitrary message format with older rsyslogd versions,
then use UDP socket to localhost IP address instead.
• udp:ip:port, to use a UDP socket. With this method it is possible to use
arbitrary message format also with older rsyslogd. When sending syslog
messages over UDP socket extra precaution needs to be taken into account, for
example, syslog daemon needs to be configured to listen on the specified UDP
port, accidental iptables rules could be interfering with local syslog traffic
and there are some security considerations that apply to UDP sockets, but do
not apply to UNIX domain sockets.
• null, to discard all messages logged to syslog.
The default is taken from the OVS_SYSLOG_METHOD environment variable; if it is unset,
the default is libc.
PKI Options
PKI configuration is required to use SSL for the connection to the database (and the
switch, if --ovs is specified).
-p privkey.pem
--private-key=privkey.pem
Specifies a PEM file containing the private key used as identity for outgoing
SSL connections.
-c cert.pem
--certificate=cert.pem
Specifies a PEM file containing a certificate that certifies the private key
specified on -p or --private-key to be trustworthy. The certificate must be
signed by the certificate authority (CA) that the peer in SSL connections will
use to verify it.
-C cacert.pem
--ca-cert=cacert.pem
Specifies a PEM file containing the CA certificate for verifying certificates
presented to this program by SSL peers. (This may be the same certificate that
SSL peers use to verify the certificate specified on -c or --certificate, or
it may be a different one, depending on the PKI design in use.)
-C none
--ca-cert=none
Disables verification of certificates presented by SSL peers. This introduces
a security risk, because it means that certificates cannot be verified to be
those of known trusted hosts.
Other Options
--db database
The OVSDB database remote to contact. If the OVN_SB_DB environment variable is set,
its value is used as the default. Otherwise, the default is unix:/db.sock, but this
default is unlikely to be useful outside of single-machine OVN test environments.
-h
--help
Prints a brief help message to the console.
-V
--version
Prints version information to the console.