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Doc: OSPF graceful restart options

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Ondrej Zajicek (work) 2019-06-30 22:11:11 +02:00
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doc/bird.sgml
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@ -3269,6 +3269,8 @@ protocol ospf [v2|v3] <name> {
tick <num>;
ecmp <switch> [limit <num>];
merge external <switch>;
graceful restart <switch>|aware;
graceful restart time <num>;
area <id> {
stub;
nssa;
@ -3412,6 +3414,31 @@ protocol ospf [v2|v3] <name> {
from different LSAs are treated as separate even if they represents the
same destination. Default value is no.
<tag><label id="ospf-graceful-restart">graceful restart <m/switch/|aware</tag>
When an OSPF instance is restarted, neighbors break adjacencies and
recalculate their routing tables, which disrupts packet forwarding even
when the forwarding plane of the restarting router remains intact.
<rfc id="3623"> specifies a graceful restart mechanism to alleviate this
issue. For OSPF graceful restart, restarting router originates
Grace-LSAs, announcing intent to do graceful restart. Neighbors
receiving these LSAs enter helper mode, in which they ignore breakdown
of adjacencies, behave as if nothing is happening and keep old routes.
When adjacencies are reestablished, the restarting router flushes
Grace-LSAs and graceful restart is ended.
This option controls the graceful restart mechanism. It has three
states: Disabled, when no support is provided. Aware, when graceful
restart helper mode is supported, but no local graceful restart is
allowed (i.e. helper-only role). Enabled, when the full graceful restart
support is provided (i.e. both restarting and helper role). Note that
proper support for local graceful restart requires also configuration of
other protocols. Default: aware.
<tag><label id="ospf-graceful-restart-time">graceful restart time <m/num/</tag>
The restart time is announced in the Grace-LSA and specifies how long
neighbors should wait for proper end of the graceful restart before
exiting helper mode prematurely. Default: 120 seconds.
<tag><label id="ospf-area">area <M>id</M></tag>
This defines an OSPF area with given area ID (an integer or an IPv4
address, similarly to a router ID). The most important area is the