ovn-trace(8) OVN Manual ovn-trace(8)
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 origi‐
nates at a logical port, what will happen to it and where will it ulti‐
mately end up? Users already familiar with the Open vSwitch of‐‐
proto/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 differ‐
ently 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 op‐
tional datapath) arguments on the command line. In this case, it simu‐
lates 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 data‐
path. 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 prerequi‐
sites; 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 in‐‐
port and eth.dst, plus eth.src if port security is enabled. For exam‐
ple:
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 >gt;>gt; 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, dis‐
played 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 sin‐
gle 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 ta‐
ble 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 in‐
cluding 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 with‐
out 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 ta‐
ble 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 dis‐
tributed 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 ac‐
tion.
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 con‐
nects 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-ar‐‐
chitecture(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 or‐
dinarily matches only one of these.
• Some logical flows can map to the Open vSwitch ``conjunc‐
tive 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 logi‐
cal ports. These flows will never show up in a trace.
• When ovn-trace omits uninteresting logical flows from out‐
put, 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 ad‐
dress 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 fire‐
wall. 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 op‐
tions 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 pid‐
file already exists and is locked by a running process, the dae‐
mon 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 (SIGA‐‐
BRT, 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 func‐
tions without it.
--no-chdir
By default, when --detach is specified, the daemon changes its
current working directory to the root directory after it de‐
taches. 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 addi‐
tional 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 speci‐
fied module.
• syslog, console, or file, to limit the log level change to
only to the system log, to the console, or to a file, re‐
spectively. (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 --ver‐‐
bose=dbg.
-vPATTERN:destination:pattern
--verbose=PATTERN:destination:pattern
Sets the log pattern for destination to pattern. Refer to ovs-ap‐‐
pctl(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 lo‐‐
cal0 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 /usr/local/var/log/ovn/program.log.
--syslog-target=host:port
Send syslog messages to UDP port on host, in addition to the sys‐
tem syslog. The host must be a numerical IP address, not a host‐
name.
--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 mes‐
sage 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 pos‐
sible 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 ad‐
dress 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 ex‐
tra precaution needs to be taken into account, for example,
syslog daemon needs to be configured to listen on the spec‐
ified UDP port, accidental iptables rules could be inter‐
fering with local syslog traffic and there are some secu‐
rity 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 vari‐
able; 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 certi‐
fies the private key specified on -p or --private-key to be
trustworthy. The certificate must be signed by the certifi‐
cate 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 ver‐
ifying 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 environ‐
ment variable is set, its value is used as the default. Other‐
wise, 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.
OVN 24.03.90 ovn-trace ovn-trace(8)