1ovn-trace(8) OVN Manual ovn-trace(8)
2build/.PP
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8 ovn-trace - Open Virtual Network logical network tracing utility
9
11 ovn-trace [options] [datapath] microflow
12 ovn-trace [options] --detach
14
16 This utility simulates packet forwarding within an OVN logical network.
17 It can be used to run through ``what-if’’ scenarios: if a packet origi‐
18 nates at a logical port, what will happen to it and where will it ulti‐
19 mately end up? Users already familiar with the Open vSwitch
20 ofproto/trace command described in ovs-vswitch(8) will find ovn-trace
21 to be a similar tool for logical networks.
22 ovn-trace works by reading the Logical_Flow and other tables from the
24 OVN southbound database (see ovn-sb(5)). It simulates a packet’s path
25 through logical networks by repeatedly looking it up in the logical
26 flow table, following the entire tree of possibilities.
27 ovn-trace simulates only the OVN logical network. It does not simulate
29 the physical elements on which the logical network is layered. This
30 means that, for example, it is unimportant how VMs are distributed
31 among hypervisors, or whether their hypervisors are functioning and
32 reachable, so ovn-trace will yield the same results regardless. There
33 is one important exception: ovn-northd, the daemon that generates the
34 logical flows that ovn-trace simulates, treats logical ports differ‐
35 ently based on whether they are up or down. Thus, if you see surprising
36 results, ensure that the ports involved in a simulation are up.
37 The simplest way to use ovn-trace is to provide the microflow (and
39 optional datapath) arguments on the command line. In this case, it sim‐
40 ulates the behavior of a single packet and exits. For an alternate
41 usage model, see Daemon Mode below.
42 The optional datapath argument specifies the name of a logical data‐
44 path. Acceptable names are the name from the northbound Logical_Switch
45 or Logical_Router table, the UUID of a record from one of those tables,
46 or the UUID of a record from the southbound Datapath_Binding table.
47 (The datapath is optional because ovn-trace can figure it out from the
48 inport that the microflow matches.)
49 The microflow argument describes the packet whose forwarding is to be
51 simulated, in the syntax of an OVN logical expression, as described in
52 ovn-sb(5), to express constraints. The parser understands prerequi‐
53 sites; for example, if the expression refers to ip4.src, there is no
54 need to explicitly state ip4 or eth.type == 0x800.
55 For reasonable L2 behavior, the microflow should include at least
57 inport and eth.dst, plus eth.src if port security is enabled. For exam‐
58 ple:
59 inport == "lp11" && eth.src == 00:01:02:03:04:05 && eth.dst == ff:ff:ff:ff:ff:ff
61 For reasonable L3 behavior, microflow should also include ip4.src and
64 ip4.dst (or ip6.src and ip6.dst) and ip.ttl. For example:
65 inport == "lp111" && eth.src == f0:00:00:00:01:11 && eth.dst == 00:00:00:00:ff:11
67 && ip4.src == 192.168.11.1 && ip4.dst == 192.168.22.2 && ip.ttl == 64
68 Here’s an ARP microflow example:
71 inport == "lp123"
73 && eth.dst == ff:ff:ff:ff:ff:ff && eth.src == f0:00:00:00:01:11
74 && arp.op == 1 && arp.sha == f0:00:00:00:01:11 && arp.spa == 192.168.1.11
75 && arp.tha == ff:ff:ff:ff:ff:ff && arp.tpa == 192.168.2.22
76 ovn-trace will reject erroneous microflow expressions, which beyond
79 syntax errors fall into two categories. First, they can be ambiguous.
80 For example, tcp.src == 80 is ambiguous because it does not state IPv4
81 or IPv6 as the Ethernet type. ip4 && tcp.src > 1024 is also ambiguous
82 because it does not constrain bits of tcp.src to particular values.
83 Second, they can be contradictory, e.g. ip4 && ip6.
84
86 ovn-trace supports the three different forms of output, each described
87 in a separate section below. Regardless of the selected output format,
88 ovn-trace starts the output with a line that shows the microflow being
89 traced in OpenFlow syntax.
90 Detailed Output
92 The detailed form of output is also the default form. This form groups
93 output into sections headed up by the ingress or egress pipeline being
94 traversed. Each pipeline lists each table that was visited (by number
95 and name), the ovn-northd source file and line number of the code that
96 added the flow, the match expression and priority of the logical flow
97 that was matched, and the actions that were executed.
98 The execution of OVN logical actions naturally forms a ``control
100 stack’’ that resembles that of a program in conventional programming
101 languages such as C or Java. Because the next action that calls into
102 another logical flow table for a lookup is a recursive construct, OVN
103 ``programs’’ in practice tend to form deep control stacks that, dis‐
104 played in the obvious way using additional indentation for each level,
105 quickly use up the horizontal space on all but the widest displays. To
106 make detailed output more readable, without loss of generality,
107 ovn-trace omits indentation for ``tail recursion,’’ that is, when next
108 is the last action in a logical flow, it does not indent details of the
109 next table lookup more deeply. Output still uses indentation when it is
110 needed for clarity.
111 OVN ``programs’’ traces also tend to encounter long strings of logical
113 flows with match expression 1 (which matches every packet) and the sin‐
114 gle action next;. These are uninteresting and merely clutter output, so
115 ovn-trace omits them entirely even from detailed output.
116 The following excerpt from detailed ovn-trace output shows a section
118 for a packet traversing the ingress pipeline of logical datapath ls1
119 with ingress logical port lp111. The packet matches a logical flow in
120 table 0 (aka ls_in_port_sec_l2) with priority 50 and executes next(1);
121 to pass to table 1. Tables 1 through 11 are trivial and omitted. In ta‐
122 ble 19 (aka ls_in_l2_lkup), the packet matches a flow with priority 50
123 based on its Ethernet destination address and the flow’s actions output
124 the packet to the lrp11-attachement logical port.
125 ingress(dp="ls1", inport="lp111")
127 ---------------------------------
128 0. ls_in_port_sec_l2: inport == "lp111", priority 50
129 next(1);
130 19. ls_in_l2_lkup: eth.dst == 00:00:00:00:ff:11, priority 50
131 outport = "lrp11-attachment";
132 output;
133 Summary Output
136 Summary output includes the logical pipelines visited by a packet and
137 the logical actions executed on it. Compared to the detailed output,
138 however, it removes details of tables and logical flows traversed by a
139 packet. It uses a format closer to that of a programming language and
140 does not attempt to avoid indentation. The summary output equivalent to
141 the above detailed output fragment is:
142 ingress(dp="ls1", inport="lp111") {
144 outport = "lrp11-attachment";
145 output;
146 ...
147 };
148 Minimal Output
151 Minimal output includes only actions that modify packet data (not
152 including OVN registers or metadata such as outport) and output actions
153 that actually deliver a packet to a logical port (excluding patch
154 ports). The operands of actions that modify packet data are displayed
155 reduced to constants, e.g. ip4.dst = reg0; might be show as ip4.dst =
156 192.168.0.1; if that was the value actually loaded. This yields output
157 even simpler than the summary format. (Users familiar with Open vSwitch
158 may recognize this as similar in spirit to the datapath actions listed
159 at the bottom of ofproto/trace output.)
160 The minimal output format reflects the externally seen behavior of the
162 logical networks more than it does the implementation. This makes this
163 output format the most suitable for use in regression tests, because it
164 is least likely to change when logical flow tables are rearranged with‐
165 out semantic change.
166
168 Some OVN logical actions use or update state that is not available in
169 the southbound database. ovn-trace handles these actions as described
170 below:
171 ct_next
173 By default ovn-trace treats flows as ``tracked’’ and
174 ``established.’’ See the description of the --ct option
175 for a way to override this behavior.
176 ct_dnat (without an argument)
178 Forks the pipeline. In one fork, advances to the next ta‐
179 ble as if next; were executed. The packet is not changed,
180 on the assumption that no NAT state was available. In the
181 other fork, the pipeline continues without change after
182 the ct_dnat action.
183 ct_snat (without an argument)
185 This action distinguishes between gateway routers and
186 distributed routers. A gateway router is defined as a
187 logical datapath that contains an l3gateway port; any
188 other logical datapath is a distributed router. On a
189 gateway router, ct_snat; is treated as a no-op. On a dis‐
190 tributed router, it is treated the same way as ct_dnat;.
191 ct_dnat(ip)
193 ct_snat(ip)
194 Forks the pipeline. In one fork, sets ip4.dst (or ip4.src)
195 to ip and ct.dnat (or ct.snat) to 1 and advances to the
196 next table as if next; were executed. In the other fork,
197 the pipeline continues without change after the ct_dnat (or
198 ct_snat) action.
199 ct_lb;
201 ct_lb(ip[:port]...);
202 Forks the pipeline. In one fork, sets ip4.dst (or ip6.dst)
203 to one of the load-balancer addresses and the destination
204 port to its associated port, if any, and sets ct.dnat to 1.
205 With one or more arguments, gives preference to the address
206 specified on --lb-dst, if any; without arguments, uses the
207 address and port specified on --lb-dst. In the other fork,
208 the pipeline continues without change after the ct_lb
209 action.
210 ct_commit
212 put_arp
213 put_nd
214 These actions are treated as no-ops.
215
217 If ovn-trace is invoked with the --detach option (see Daemon Options,
218 below), it runs in the background as a daemon and accepts commands from
219 ovs-appctl (or another JSON-RPC client) indefinitely. The currently
220 supported commands are described below.
221 trace [options] [datapath] microflow
223 Traces microflow through datapath and replies with the
224 results of the trace. Accepts the options described under
225 Trace Options below.
226 exit Causes ovn-trace to gracefully terminate.
228
230 Trace Options
231 --detailed
232 --summary
233 --minimal
234 These options control the form and level of detail in ovn-trace
235 output. If more than one of these options is specified, all of the
236 selected forms are output, in the order listed above, each headed
237 by a banner line. If none of these options is given, --detailed is
238 the default. See Output, above, for a description of each kind of
239 output.
240 --all
242 Selects all three forms of output.
243 --ovs[=remote]
245 Makes ovn-trace attempt to obtain and display the OpenFlow flows
246 that correspond to each OVN logical flow. To do so, ovn-trace con‐
247 nects to remote (by default, unix:/br-int.mgmt) over OpenFlow and
248 retrieves the flows. If remote is specified, it must be an active
249 OpenFlow connection method described in ovsdb(7).
250 To make the best use of the output, it is important to understand
252 the relationship between logical flows and OpenFlow flows.
253 ovn-architecture(7), under Architectural Physical Life Cycle of a
254 Packet, describes this relationship. Keep in mind the following
255 points:
256 · ovn-trace currently shows all the OpenFlow flows to which a
258 logical flow corresponds, even though an actual packet
259 ordinarily matches only one of these.
260 · Some logical flows can map to the Open vSwitch ``conjunc‐
262 tive match’’ extension (see ovs-fields(7)). Currently
263 ovn-trace cannot display the flows with conjunction actions
264 that effectively produce the conj_id match.
265 · Some logical flows may not be represented in the OpenFlow
267 tables on a given hypervisor, if they could not be used on
268 that hypervisor.
269 · Some OpenFlow flows do not correspond to logical flows,
271 such as OpenFlow flows that map between physical and logi‐
272 cal ports. These flows will never show up in a trace.
273 · When ovn-trace omits uninteresting logical flows from out‐
275 put, it does not look up the corresponding OpenFlow flows.
276 --ct=flags
278 This option sets the ct_state flags that a ct_next logical action
279 will report. The flags must be a comma- or space-separated list of
280 the following connection tracking flags:
281 · trk: Include to indicate connection tracking has taken
283 place. (This bit is set automatically even if not listed in
284 flags.
285 · new: Include to indicate a new flow.
287 · est: Include to indicate an established flow.
289 · rel: Include to indicate a related flow.
291 · rpl: Include to indicate a reply flow.
293 · inv: Include to indicate a connection entry in a bad state.
295 · dnat: Include to indicate a packet whose destination IP
297 address has been changed.
298 · snat: Include to indicate a packet whose source IP address
300 has been changed.
301 The ct_next action is used to implement the OVN distributed fire‐
303 wall. For testing, useful flag combinations include:
304 · trk,new: A packet in a flow in either direction through a
306 firewall that has not yet been committed (with ct_commit).
307 · trk,est: A packet in an established flow going out through
309 a firewall.
310 · trk,rpl: A packet coming in through a firewall in reply to
312 an established flow.
313 · trk,inv: An invalid packet in either direction.
315 A packet might pass through the connection tracker twice in one
317 trip through OVN: once following egress from a VM as it passes
318 outward through a firewall, and once preceding ingress to a second
319 VM as it passes inward through a firewall. Use multiple --ct
320 options to specify the flags for multiple ct_next actions.
321 When --ct is unspecified, or when there are fewer --ct options
323 than ct_next actions, the flags default to trk,est.
324 --lb-dst=ip[:port]
326 Sets the IP from VIP pool to use as destination of the packet.
327 --lb-dst is not available in daemon mode.
328 --select-id=id
330 Specify the id to be selected by the select action. id must be one
331 of the values listed in the select action. Otherwise, a random id
332 is selected from the list, as if --select-id were not specified.
333 --select-id is not available in daemon mode.
334 --friendly-names
336 --no-friendly-names
337 When cloud management systems such as OpenStack are layered on top
338 of OVN, they often use long, human-unfriendly names for ports and
339 datapaths, for example, ones that include entire UUIDs. They do
340 usually include friendlier names, but the long, hard-to-read names
341 are the ones that appear in matches and actions. By default, or
342 with --friendly-names, ovn-trace substitutes these friendlier
343 names for the long names in its output. Use --no-friendly-names to
344 disable this behavior; this option might be useful, for example,
345 if a program is going to parse ovn-trace output.
346 Daemon Options
348 --pidfile[=pidfile]
349 Causes a file (by default, program.pid) to be created indicating
350 the PID of the running process. If the pidfile argument is not
351 specified, or if it does not begin with /, then it is created in
352 .
353 If --pidfile is not specified, no pidfile is created.
355 --overwrite-pidfile
357 By default, when --pidfile is specified and the specified pid‐
358 file already exists and is locked by a running process, the dae‐
359 mon refuses to start. Specify --overwrite-pidfile to cause it to
360 instead overwrite the pidfile.
361 When --pidfile is not specified, this option has no effect.
363 --detach
365 Runs this program as a background process. The process forks,
366 and in the child it starts a new session, closes the standard
367 file descriptors (which has the side effect of disabling logging
368 to the console), and changes its current directory to the root
369 (unless --no-chdir is specified). After the child completes its
370 initialization, the parent exits.
371 --monitor
373 Creates an additional process to monitor this program. If it
374 dies due to a signal that indicates a programming error (SIGA‐
375 BRT, SIGALRM, SIGBUS, SIGFPE, SIGILL, SIGPIPE, SIGSEGV, SIGXCPU,
376 or SIGXFSZ) then the monitor process starts a new copy of it. If
377 the daemon dies or exits for another reason, the monitor process
378 exits.
379 This option is normally used with --detach, but it also func‐
381 tions without it.
382 --no-chdir
384 By default, when --detach is specified, the daemon changes its
385 current working directory to the root directory after it
386 detaches. Otherwise, invoking the daemon from a carelessly cho‐
387 sen directory would prevent the administrator from unmounting
388 the file system that holds that directory.
389 Specifying --no-chdir suppresses this behavior, preventing the
391 daemon from changing its current working directory. This may be
392 useful for collecting core files, since it is common behavior to
393 write core dumps into the current working directory and the root
394 directory is not a good directory to use.
395 This option has no effect when --detach is not specified.
397 --no-self-confinement
399 By default this daemon will try to self-confine itself to work
400 with files under well-known directories determined at build
401 time. It is better to stick with this default behavior and not
402 to use this flag unless some other Access Control is used to
403 confine daemon. Note that in contrast to other access control
404 implementations that are typically enforced from kernel-space
405 (e.g. DAC or MAC), self-confinement is imposed from the user-
406 space daemon itself and hence should not be considered as a full
407 confinement strategy, but instead should be viewed as an addi‐
408 tional layer of security.
409 --user=user:group
411 Causes this program to run as a different user specified in
412 user:group, thus dropping most of the root privileges. Short
413 forms user and :group are also allowed, with current user or
414 group assumed, respectively. Only daemons started by the root
415 user accepts this argument.
416 On Linux, daemons will be granted CAP_IPC_LOCK and
418 CAP_NET_BIND_SERVICES before dropping root privileges. Daemons
419 that interact with a datapath, such as ovs-vswitchd, will be
420 granted three additional capabilities, namely CAP_NET_ADMIN,
421 CAP_NET_BROADCAST and CAP_NET_RAW. The capability change will
422 apply even if the new user is root.
423 On Windows, this option is not currently supported. For security
425 reasons, specifying this option will cause the daemon process
426 not to start.
427 Logging Options
429 -v[spec]
430 --verbose=[spec]
431 Sets logging levels. Without any spec, sets the log level for
432 every module and destination to dbg. Otherwise, spec is a list of
433 words separated by spaces or commas or colons, up to one from each
434 category below:
435 · A valid module name, as displayed by the vlog/list command
437 on ovs-appctl(8), limits the log level change to the speci‐
438 fied module.
439 · syslog, console, or file, to limit the log level change to
441 only to the system log, to the console, or to a file,
442 respectively. (If --detach is specified, the daemon closes
443 its standard file descriptors, so logging to the console
444 will have no effect.)
445 On Windows platform, syslog is accepted as a word and is
447 only useful along with the --syslog-target option (the word
448 has no effect otherwise).
449 · off, emer, err, warn, info, or dbg, to control the log
451 level. Messages of the given severity or higher will be
452 logged, and messages of lower severity will be filtered
453 out. off filters out all messages. See ovs-appctl(8) for a
454 definition of each log level.
455 Case is not significant within spec.
457 Regardless of the log levels set for file, logging to a file will
459 not take place unless --log-file is also specified (see below).
460 For compatibility with older versions of OVS, any is accepted as a
462 word but has no effect.
463 -v
465 --verbose
466 Sets the maximum logging verbosity level, equivalent to --ver‐
467 bose=dbg.
468 -vPATTERN:destination:pattern
470 --verbose=PATTERN:destination:pattern
471 Sets the log pattern for destination to pattern. Refer to
472 ovs-appctl(8) for a description of the valid syntax for pattern.
473 -vFACILITY:facility
475 --verbose=FACILITY:facility
476 Sets the RFC5424 facility of the log message. facility can be one
477 of kern, user, mail, daemon, auth, syslog, lpr, news, uucp, clock,
478 ftp, ntp, audit, alert, clock2, local0, local1, local2, local3,
479 local4, local5, local6 or local7. If this option is not specified,
480 daemon is used as the default for the local system syslog and
481 local0 is used while sending a message to the target provided via
482 the --syslog-target option.
483 --log-file[=file]
485 Enables logging to a file. If file is specified, then it is used
486 as the exact name for the log file. The default log file name used
487 if file is omitted is /var/log/ovn/program.log.
488 --syslog-target=host:port
490 Send syslog messages to UDP port on host, in addition to the sys‐
491 tem syslog. The host must be a numerical IP address, not a host‐
492 name.
493 --syslog-method=method
495 Specify method as how syslog messages should be sent to syslog
496 daemon. The following forms are supported:
497 · libc, to use the libc syslog() function. Downside of using
499 this options is that libc adds fixed prefix to every mes‐
500 sage before it is actually sent to the syslog daemon over
501 /dev/log UNIX domain socket.
502 · unix:file, to use a UNIX domain socket directly. It is pos‐
504 sible to specify arbitrary message format with this option.
505 However, rsyslogd 8.9 and older versions use hard coded
506 parser function anyway that limits UNIX domain socket use.
507 If you want to use arbitrary message format with older
508 rsyslogd versions, then use UDP socket to localhost IP
509 address instead.
510 · udp:ip:port, to use a UDP socket. With this method it is
512 possible to use arbitrary message format also with older
513 rsyslogd. When sending syslog messages over UDP socket
514 extra precaution needs to be taken into account, for exam‐
515 ple, syslog daemon needs to be configured to listen on the
516 specified UDP port, accidental iptables rules could be
517 interfering with local syslog traffic and there are some
518 security considerations that apply to UDP sockets, but do
519 not apply to UNIX domain sockets.
520 · null, to discard all messages logged to syslog.
522 The default is taken from the OVS_SYSLOG_METHOD environment vari‐
524 able; if it is unset, the default is libc.
525 PKI Options
527 PKI configuration is required to use SSL for the connection to the
528 database (and the switch, if --ovs is specified).
529 -p privkey.pem
531 --private-key=privkey.pem
532 Specifies a PEM file containing the private key used as
533 identity for outgoing SSL connections.
534 -c cert.pem
536 --certificate=cert.pem
537 Specifies a PEM file containing a certificate that certi‐
538 fies the private key specified on -p or --private-key to be
539 trustworthy. The certificate must be signed by the certifi‐
540 cate authority (CA) that the peer in SSL connections will
541 use to verify it.
542 -C cacert.pem
544 --ca-cert=cacert.pem
545 Specifies a PEM file containing the CA certificate for ver‐
546 ifying certificates presented to this program by SSL peers.
547 (This may be the same certificate that SSL peers use to
548 verify the certificate specified on -c or --certificate, or
549 it may be a different one, depending on the PKI design in
550 use.)
551 -C none
553 --ca-cert=none
554 Disables verification of certificates presented by SSL
555 peers. This introduces a security risk, because it means
556 that certificates cannot be verified to be those of known
557 trusted hosts.
558 Other Options
560 --db database
561 The OVSDB database remote to contact. If the OVN_SB_DB environ‐
562 ment variable is set, its value is used as the default. Other‐
563 wise, the default is unix:/db.sock, but this default is unlikely
564 to be useful outside of single-machine OVN test environments.
565 -h
567 --help
568 Prints a brief help message to the console.
569 -V
571 --version
572 Prints version information to the console.
573OVN 20.12.0 ovn-trace ovn-trace(8)