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Documentation (and minor fixes) for BGP graceful restart.
This commit is contained in:
Ondrej Zajicek
parent
0c791f873a
commit
6eda3f135f
@ -157,6 +157,9 @@ options. The most important ones are:
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<tag>-f</tag>
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run bird in foreground.
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<tag>-R</tag>
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apply graceful restart recovery after start.
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</descrip>
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<p>BIRD writes messages about its work to log files or syslog (according to config).
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@ -187,6 +190,7 @@ configuration, but it is generally easy -- BIRD needs just the
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standard library, privileges to read the config file and create the
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control socket and the CAP_NET_* capabilities.
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<chapt>About routing tables
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<p>BIRD has one or more routing tables which may or may not be
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@ -242,6 +246,20 @@ using comparison and ordering). Minor advantage is that routes are
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shown sorted in <cf/show route/, minor disadvantage is that it is
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slightly more computationally expensive.
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<sect>Graceful restart
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<p>When BIRD is started after restart or crash, it repopulates routing tables in
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an uncoordinated manner, like after clean start. This may be impractical in some
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cases, because if the forwarding plane (i.e. kernel routing tables) remains
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intact, then its synchronization with BIRD would temporarily disrupt packet
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forwarding until protocols converge. Graceful restart is a mechanism that could
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help with this issue. Generally, it works by starting protocols and letting them
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repopulate routing tables while deferring route propagation until protocols
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acknowledge their convergence. Note that graceful restart behavior have to be
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configured for all relevant protocols and requires protocol-specific support
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(currently implemented for Kernel and BGP protocols), it is activated for
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particular boot by option <cf/-R/.
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<chapt>Configuration
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@ -371,6 +389,12 @@ protocol rip {
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would accept IPv6 routes only). Such behavior was default in
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older versions of BIRD.
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<tag>graceful restart wait <m/number/</tag>
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During graceful restart recovery, BIRD waits for convergence of routing
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protocols. This option allows to specify a timeout for the recovery to
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prevent waiting indefinitely if some protocols cannot converge. Default:
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240 seconds.
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<tag>timeformat route|protocol|base|log "<m/format1/" [<m/limit/ "<m/format2/"]</tag>
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This option allows to specify a format of date/time used by
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BIRD. The first argument specifies for which purpose such
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@ -1493,6 +1517,8 @@ extended communities
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(RFC 4360<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4360.txt">),
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route reflectors
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(RFC 4456<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4456.txt">),
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graceful restart
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(RFC 4724<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4724.txt">),
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multiprotocol extensions
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(RFC 4760<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">),
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4B AS numbers
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@ -1502,9 +1528,7 @@ and 4B AS numbers in extended communities
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For IPv6, it uses the standard multiprotocol extensions defined in
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RFC 2283<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2283.txt">
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including changes described in the
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latest draft<htmlurl url="ftp://ftp.rfc-editor.org/internet-drafts/draft-ietf-idr-bgp4-multiprotocol-v2-05.txt">
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RFC 4760<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc4760.txt">
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and applied to IPv6 according to
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RFC 2545<htmlurl url="ftp://ftp.rfc-editor.org/in-notes/rfc2545.txt">.
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@ -1716,6 +1740,26 @@ for each neighbor using the following configuration parameters:
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capability and accepts such requests. Even when disabled, BIRD
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can send route refresh requests. Default: on.
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<tag>graceful restart <m/switch/|aware</tag>
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When a BGP speaker restarts or crashes, neighbors will discard all
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received paths from the speaker, which disrupts packet forwarding even
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when the forwarding plane of the speaker remains intact. RFC 4724
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specifies an optional graceful restart mechanism to alleviate this
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issue. This option controls the mechanism. It has three states:
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Disabled, when no support is provided. Aware, when the graceful restart
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support is announced and the support for restarting neighbors is
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provided, but no local graceful restart is allowed (i.e. receiving-only
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role). Enabled, when the full graceful restart support is provided
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(i.e. both restarting and receiving role). Note that proper support for
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local graceful restart requires also configuration of other protocols.
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Default: aware.
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<tag>graceful restart time <m/number/</tag>
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The restart time is announced in the BGP graceful restart capability
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and specifies how long the neighbor would wait for the BGP session to
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re-establish after a restart before deleting stale routes. Default:
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120 seconds.
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<tag>interpret communities <m/switch/</tag> RFC 1997 demands
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that BGP speaker should process well-known communities like
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no-export (65535, 65281) or no-advertise (65535, 65282). For
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@ -2063,25 +2107,36 @@ overcome using another routing table and the pipe protocol.
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<sect1>Configuration
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<p><descrip>
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<tag>persist <m/switch/</tag> Tell BIRD to leave all its routes in the
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routing tables when it exits (instead of cleaning them up).
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<tag>scan time <m/number/</tag> Time in seconds between two consecutive scans of the
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kernel routing table.
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<tag>learn <m/switch/</tag> Enable learning of routes added to the kernel
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routing tables by other routing daemons or by the system administrator.
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This is possible only on systems which support identification of route
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authorship.
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<tag>persist <m/switch/</tag>
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Tell BIRD to leave all its routes in the routing tables when it exits
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(instead of cleaning them up).
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<tag>device routes <m/switch/</tag> Enable export of device
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routes to the kernel routing table. By default, such routes
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are rejected (with the exception of explicitly configured
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device routes from the static protocol) regardless of the
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export filter to protect device routes in kernel routing table
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(managed by OS itself) from accidental overwriting or erasing.
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<tag>scan time <m/number/</tag>
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Time in seconds between two consecutive scans of the kernel routing
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table.
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<tag>kernel table <m/number/</tag> Select which kernel table should
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this particular instance of the Kernel protocol work with. Available
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only on systems supporting multiple routing tables.
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<tag>learn <m/switch/</tag>
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Enable learning of routes added to the kernel routing tables by other
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routing daemons or by the system administrator. This is possible only on
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systems which support identification of route authorship.
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<tag>device routes <m/switch/</tag>
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Enable export of device routes to the kernel routing table. By default,
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such routes are rejected (with the exception of explicitly configured
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device routes from the static protocol) regardless of the export filter
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to protect device routes in kernel routing table (managed by OS itself)
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from accidental overwriting or erasing.
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<tag>kernel table <m/number/</tag>
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Select which kernel table should this particular instance of the Kernel
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protocol work with. Available only on systems supporting multiple
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routing tables.
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<tag>graceful restart <m/switch/</tag>
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Participate in graceful restart recovery. If this option is enabled and
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a graceful restart recovery is active, the Kernel protocol will defer
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synchronization of routing tables until the end of the recovery. Note
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that import of kernel routes to BIRD is not affected.
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</descrip>
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<sect1>Attributes
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154
nest/proto.c
154
nest/proto.c
@ -51,6 +51,8 @@ static char *c_states[] = { "HUNGRY", "???", "HAPPY", "FLUSHING" };
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static void proto_flush_loop(void *);
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static void proto_shutdown_loop(struct timer *);
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static void proto_rethink_goal(struct proto *p);
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static void proto_want_export_up(struct proto *p);
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static void proto_fell_down(struct proto *p);
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static char *proto_state_name(struct proto *p);
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static void
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@ -151,21 +153,20 @@ extern pool *rt_table_pool;
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* @t: routing table to connect to
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* @stats: per-table protocol statistics
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*
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* This function creates a connection between the protocol instance @p
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* and the routing table @t, making the protocol hear all changes in
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* the table.
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* This function creates a connection between the protocol instance @p and the
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* routing table @t, making the protocol hear all changes in the table.
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*
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* The announce hook is linked in the protocol ahook list and, if the
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* protocol accepts routes, also in the table ahook list. Announce
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* hooks are allocated from the routing table resource pool, they are
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* unlinked from the table ahook list after the protocol went down,
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* (in proto_schedule_flush()) and they are automatically freed after the
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* protocol is flushed (in proto_fell_down()).
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* The announce hook is linked in the protocol ahook list. Announce hooks are
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* allocated from the routing table resource pool and when protocol accepts
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* routes also in the table ahook list. The are linked to the table ahook list
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* and unlinked from it depending on export_state (in proto_want_export_up() and
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* proto_want_export_down()) and they are automatically freed after the protocol
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* is flushed (in proto_fell_down()).
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*
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* Unless you want to listen to multiple routing tables (as the Pipe
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* protocol does), you needn't to worry about this function since the
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* connection to the protocol's primary routing table is initialized
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* automatically by the core code.
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* Unless you want to listen to multiple routing tables (as the Pipe protocol
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* does), you needn't to worry about this function since the connection to the
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* protocol's primary routing table is initialized automatically by the core
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* code.
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*/
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struct announce_hook *
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proto_add_announce_hook(struct proto *p, struct rtable *t, struct proto_stats *stats)
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@ -183,7 +184,7 @@ proto_add_announce_hook(struct proto *p, struct rtable *t, struct proto_stats *s
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h->next = p->ahooks;
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p->ahooks = h;
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if (p->rt_notify && (p->export_state == ES_READY))
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if (p->rt_notify && (p->export_state != ES_DOWN))
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add_tail(&t->hooks, &h->n);
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return h;
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}
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@ -659,16 +660,59 @@ proto_rethink_goal(struct proto *p)
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}
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/**
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* DOC: Graceful restart recovery
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*
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* Graceful restart of a router is a process when the routing plane (e.g. BIRD)
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* restarts but both the forwarding plane (e.g kernel routing table) and routing
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* neighbors keep proper routes, and therefore uninterrupted packet forwarding
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* is maintained.
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*
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* BIRD implements graceful restart recovery by deferring export of routes to
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* protocols until routing tables are refilled with the expected content. After
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* start, protocols generate routes as usual, but routes are not propagated to
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* them, until protocols report that they generated all routes. After that,
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* graceful restart recovery is finished and the export (and the initial feed)
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* to protocols is enabled.
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*
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* When graceful restart recovery need is detected during initialization, then
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* enabled protocols are marked with @gr_recovery flag before start. Such
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* protocols then decide how to proceed with graceful restart, participation is
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* voluntary. Protocols could lock the recovery by proto_graceful_restart_lock()
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* (stored in @gr_lock flag), which means that they want to postpone the end of
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* the recovery until they converge and then unlock it. They also could set
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* @gr_wait before advancing to %PS_UP, which means that the core should defer
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* route export to that protocol until the end of the recovery. This should be
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* done by protocols that expect their neigbors to keep the proper routes
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* (kernel table, BGP sessions with BGP graceful restart capability).
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*
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* The graceful restart recovery is finished when either all graceful restart
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* locks are unlocked or when graceful restart wait timer fires.
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*
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*/
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static void graceful_restart_done(struct timer *t UNUSED);
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static void proto_want_export_up(struct proto *p);
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static void graceful_restart_done(struct timer *t);
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/**
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* graceful_restart_recovery - request initial graceful restart recovery
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*
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* Called by the platform initialization code if the need for recovery
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* after graceful restart is detected during boot. Have to be called
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* before protos_commit().
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*/
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void
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graceful_restart_recovery(void)
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{
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graceful_restart_state = GRS_INIT;
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}
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/**
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* graceful_restart_init - initialize graceful restart
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*
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* When graceful restart recovery was requested, the function starts an active
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* phase of the recovery and initializes graceful restart wait timer. The
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* function have to be called after protos_commit().
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*/
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void
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graceful_restart_init(void)
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{
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@ -689,6 +733,15 @@ graceful_restart_init(void)
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tm_start(gr_wait_timer, config->gr_wait);
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}
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/**
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* graceful_restart_done - finalize graceful restart
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*
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* When there are no locks on graceful restart, the functions finalizes the
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* graceful restart recovery. Protocols postponing route export until the end of
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* the recovery are awakened and the export to them is enabled. All other
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* related state is cleared. The function is also called when the graceful
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* restart wait timer fires (but there are still some locks).
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*/
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static void
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graceful_restart_done(struct timer *t UNUSED)
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{
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@ -727,7 +780,19 @@ graceful_restart_show_status(void)
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cli_msg(-24, " Wait timer is %d/%d", tm_remains(gr_wait_timer), config->gr_wait);
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}
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/* Just from start hook */
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/**
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* proto_graceful_restart_lock - lock graceful restart by protocol
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* @p: protocol instance
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*
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* This function allows a protocol to postpone the end of graceful restart
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* recovery until it converges. The lock is removed when the protocol calls
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* proto_graceful_restart_unlock() or when the protocol is stopped.
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*
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* The function have to be called during the initial phase of graceful restart
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* recovery and only for protocols that are part of graceful restart (i.e. their
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* @gr_recovery is set), which means it should be called from protocol start
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* hooks.
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*/
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void
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proto_graceful_restart_lock(struct proto *p)
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{
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@ -741,6 +806,13 @@ proto_graceful_restart_lock(struct proto *p)
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graceful_restart_locks++;
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}
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/**
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* proto_graceful_restart_unlock - unlock graceful restart by protocol
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* @p: protocol instance
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*
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* This function unlocks a lock from proto_graceful_restart_lock(). It is also
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* automatically called when the lock holding protocol went down.
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*/
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void
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proto_graceful_restart_unlock(struct proto *p)
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{
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@ -867,29 +939,6 @@ protos_build(void)
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proto_flush_event->hook = proto_flush_loop;
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proto_shutdown_timer = tm_new(proto_pool);
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proto_shutdown_timer->hook = proto_shutdown_loop;
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proto_shutdown_timer = tm_new(proto_pool);
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proto_shutdown_timer->hook = proto_shutdown_loop;
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}
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static void
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proto_fell_down(struct proto *p)
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{
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DBG("Protocol %s down\n", p->name);
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u32 all_routes = p->stats.imp_routes + p->stats.filt_routes;
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if (all_routes != 0)
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log(L_ERR "Protocol %s is down but still has %d routes", p->name, all_routes);
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bzero(&p->stats, sizeof(struct proto_stats));
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proto_free_ahooks(p);
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if (! p->proto->multitable)
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rt_unlock_table(p->table);
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if (p->proto->cleanup)
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p->proto->cleanup(p);
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proto_rethink_goal(p);
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}
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static void
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@ -1066,6 +1115,10 @@ proto_request_feeding(struct proto *p)
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{
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ASSERT(p->proto_state == PS_UP);
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/* Do nothing if we are still waiting for feeding */
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if (p->export_state == ES_DOWN)
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return;
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/* If we are already feeding, we want to restart it */
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if (p->export_state == ES_FEEDING)
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{
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@ -1220,6 +1273,27 @@ proto_falling_down(struct proto *p)
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proto_graceful_restart_unlock(p);
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}
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static void
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proto_fell_down(struct proto *p)
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{
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DBG("Protocol %s down\n", p->name);
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u32 all_routes = p->stats.imp_routes + p->stats.filt_routes;
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if (all_routes != 0)
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log(L_ERR "Protocol %s is down but still has %d routes", p->name, all_routes);
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bzero(&p->stats, sizeof(struct proto_stats));
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proto_free_ahooks(p);
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if (! p->proto->multitable)
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rt_unlock_table(p->table);
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if (p->proto->cleanup)
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p->proto->cleanup(p);
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proto_rethink_goal(p);
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}
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/**
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* proto_notify_state - notify core about protocol state change
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@ -1110,6 +1110,21 @@ rt_examine(rtable *t, ip_addr prefix, int pxlen, struct proto *p, struct filter
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return v > 0;
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}
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/**
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* rt_refresh_begin - start a refresh cycle
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* @t: related routing table
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* @ah: related announce hook
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*
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* This function starts a refresh cycle for given routing table and announce
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* hook. The refresh cycle is a sequence where the protocol sends all its valid
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* routes to the routing table (by rte_update()). After that, all protocol
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* routes (more precisely routes with @ah as @sender) not sent during the
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* refresh cycle but still in the table from the past are pruned. This is
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* implemented by marking all related routes as stale by REF_STALE flag in
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* rt_refresh_begin(), then marking all related stale routes with REF_DISCARD
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* flag in rt_refresh_end() and then removing such routes in the prune loop.
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*/
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void
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rt_refresh_begin(rtable *t, struct announce_hook *ah)
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{
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@ -1126,6 +1141,14 @@ rt_refresh_begin(rtable *t, struct announce_hook *ah)
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FIB_WALK_END;
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}
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/**
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* rt_refresh_end - end a refresh cycle
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* @t: related routing table
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* @ah: related announce hook
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*
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* This function starts a refresh cycle for given routing table and announce
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* hook. See rt_refresh_begin() for description of refresh cycles.
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*/
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void
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rt_refresh_end(rtable *t, struct announce_hook *ah)
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{
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@ -1405,6 +1428,19 @@ again:
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return 1;
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}
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/**
|
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* rt_prune_table - prune a routing table
|
||||
*
|
||||
* This function scans the routing table @tab and removes routes belonging to
|
||||
* flushing protocols, discarded routes and also stale network entries, in a
|
||||
* similar fashion like rt_prune_loop(). Returns 1 when all such routes are
|
||||
* pruned. Contrary to rt_prune_loop(), this function is not a part of the
|
||||
* protocol flushing loop, but it is called from rt_event() for just one routing
|
||||
* table.
|
||||
*
|
||||
* Note that rt_prune_table() and rt_prune_loop() share (for each table) the
|
||||
* prune state (@prune_state) and also the pruning iterator (@prune_fit).
|
||||
*/
|
||||
static inline int
|
||||
rt_prune_table(rtable *tab)
|
||||
{
|
||||
@ -1415,16 +1451,15 @@ rt_prune_table(rtable *tab)
|
||||
/**
|
||||
* rt_prune_loop - prune routing tables
|
||||
*
|
||||
* The prune loop scans routing tables and removes routes belonging to
|
||||
* flushing protocols and also stale network entries. Returns 1 when
|
||||
* all such routes are pruned. It is a part of the protocol flushing
|
||||
* loop.
|
||||
* The prune loop scans routing tables and removes routes belonging to flushing
|
||||
* protocols, discarded routes and also stale network entries. Returns 1 when
|
||||
* all such routes are pruned. It is a part of the protocol flushing loop.
|
||||
*
|
||||
* The prune loop runs in two steps. In the first step it prunes just
|
||||
* the routes with flushing senders (in explicitly marked tables) so
|
||||
* the route removal is propagated as usual. In the second step, all
|
||||
* remaining relevant routes are removed. Ideally, there shouldn't be
|
||||
* any, but it happens when pipe filters are changed.
|
||||
* The prune loop runs in two steps. In the first step it prunes just the routes
|
||||
* with flushing senders (in explicitly marked tables) so the route removal is
|
||||
* propagated as usual. In the second step, all remaining relevant routes are
|
||||
* removed. Ideally, there shouldn't be any, but it happens when pipe filters
|
||||
* are changed.
|
||||
*/
|
||||
int
|
||||
rt_prune_loop(void)
|
||||
|
||||
@ -51,6 +51,16 @@
|
||||
* and bgp_encode_attrs() which does the converse. Both functions are built around a
|
||||
* @bgp_attr_table array describing all important characteristics of all known attributes.
|
||||
* Unknown transitive attributes are attached to the route as %EAF_TYPE_OPAQUE byte streams.
|
||||
*
|
||||
* BGP protocol implements graceful restart in both restarting (local restart)
|
||||
* and receiving (neighbor restart) roles. The first is handled mostly by the
|
||||
* graceful restart code in the nest, BGP protocol just handles capabilities,
|
||||
* sets @gr_wait and locks graceful restart until end-of-RIB mark is received.
|
||||
* The second is implemented by internal restart of the BGP state to %BS_IDLE
|
||||
* and protocol state to %PS_START, but keeping the protocol up from the core
|
||||
* point of view and therefore maintaining received routes. Routing table
|
||||
* refresh cycle (rt_refresh_begin(), rt_refresh_end()) is used for removing
|
||||
* stale routes after reestablishment of BGP session during graceful restart.
|
||||
*/
|
||||
|
||||
#undef LOCAL_DEBUG
|
||||
@ -431,6 +441,17 @@ bgp_conn_enter_idle_state(struct bgp_conn *conn)
|
||||
bgp_conn_leave_established_state(p);
|
||||
}
|
||||
|
||||
/**
|
||||
* bgp_handle_graceful_restart - handle detected BGP graceful restart
|
||||
* @p: BGP instance
|
||||
*
|
||||
* This function is called when a BGP graceful restart of the neighbor is
|
||||
* detected (when the TCP connection fails or when a new TCP connection
|
||||
* appears). The function activates processing of the restart - starts routing
|
||||
* table refresh cycle and activates BGP restart timer. The protocol state goes
|
||||
* back to %PS_START, but changing BGP state back to %BS_IDLE is left for the
|
||||
* caller.
|
||||
*/
|
||||
void
|
||||
bgp_handle_graceful_restart(struct bgp_proto *p)
|
||||
{
|
||||
@ -448,6 +469,16 @@ bgp_handle_graceful_restart(struct bgp_proto *p)
|
||||
rt_refresh_begin(p->p.main_ahook->table, p->p.main_ahook);
|
||||
}
|
||||
|
||||
/**
|
||||
* bgp_graceful_restart_done - finish active BGP graceful restart
|
||||
* @p: BGP instance
|
||||
*
|
||||
* This function is called when the active BGP graceful restart of the neighbor
|
||||
* should be finished - either successfully (the neighbor sends all paths and
|
||||
* reports end-of-RIB on the new session) or unsuccessfully (the neighbor does
|
||||
* not support BGP graceful restart on the new session). The function ends
|
||||
* routing table refresh cycle and stops BGP restart timer.
|
||||
*/
|
||||
void
|
||||
bgp_graceful_restart_done(struct bgp_proto *p)
|
||||
{
|
||||
@ -457,6 +488,15 @@ bgp_graceful_restart_done(struct bgp_proto *p)
|
||||
rt_refresh_end(p->p.main_ahook->table, p->p.main_ahook);
|
||||
}
|
||||
|
||||
/**
|
||||
* bgp_graceful_restart_timeout - timeout of graceful restart 'restart timer'
|
||||
* @t: timer
|
||||
*
|
||||
* This function is a timeout hook for @gr_timer, implementing BGP restart time
|
||||
* limit for reestablisment of the BGP session after the graceful restart. When
|
||||
* fired, we just proceed with the usual protocol restart.
|
||||
*/
|
||||
|
||||
static void
|
||||
bgp_graceful_restart_timeout(timer *t)
|
||||
{
|
||||
@ -968,7 +1008,7 @@ bgp_start(struct proto *P)
|
||||
p->remote_id = 0;
|
||||
p->source_addr = p->cf->source_addr;
|
||||
|
||||
if (P->gr_recovery)
|
||||
if (p->p.gr_recovery && p->cf->gr_mode)
|
||||
proto_graceful_restart_lock(P);
|
||||
|
||||
/*
|
||||
|
||||
Loading…
Reference in New Issue
Block a user