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Doc: Update documentation about VRFs and BFD

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Ondrej Zajicek (work) 2019-08-01 01:02:31 +02:00
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doc/bird.sgml
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@ -599,14 +599,23 @@ agreement").
<tag><label id="proto-table">table <m/name/</tag>
Connect this protocol to a non-default routing table.
<tag><label id="proto-vrf">vrf "<m/text/"</tag>
<tag><label id="proto-vrf">vrf "<m/text/"|default</tag>
Associate the protocol with specific VRF. The protocol will be
restricted to interfaces assigned to the VRF and will use sockets bound
to the VRF. Appropriate VRF interface must exist on OS level. For kernel
protocol, an appropriate table still must be explicitly selected by
<cf/table/ option. Note that for proper VRF support it is necessary to
use Linux kernel version at least 4.14, older versions have limited
VRF implementation.
to the VRF. A corresponding VRF interface must exist on OS level. For
kernel protocol, an appropriate table still must be explicitly selected
by <cf/table/ option.
By selecting <cf/default/, the protocol is associated with the default
VRF; i.e., it will be restricted to interfaces not assigned to any
regular VRF. That is different from not specifying <cf/vrf/ at all, in
which case the protocol may use any interface regardless of its VRF
status.
Note that for proper VRF support it is necessary to use Linux kernel
version at least 4.14, older versions have limited VRF implementation.
Before Linux kernel 5.0, a socket bound to a port in default VRF collide
with others in regular VRFs.
</descrip>
<p>There are several options that give sense only with certain protocols:
@ -1624,7 +1633,7 @@ in the future. Also note that we currently support at most one protocol instance
<p>BFD packets are sent with a dynamic source port number. Linux systems use by
default a bit different dynamic port range than the IANA approved one
(49152-65535). If you experience problems with compatibility, please adjust
<cf>/proc/sys/net/ipv4/ip_local_port_range</cf>
<cf>/proc/sys/net/ipv4/ip_local_port_range</cf>.
<sect1>Configuration
<label id="bfd-config">
@ -1641,6 +1650,14 @@ configuration is often sufficient.
<p>Note that to use BFD for other protocols like OSPF or BGP, these protocols
also have to be configured to request BFD sessions, usually by <cf/bfd/ option.
<p>A BFD instance not associated with any VRF handles session requests from all
other protocols, even ones associated with a VRF. Such setup would work for
single-hop BFD sessions if <cf/net.ipv4.udp_l3mdev_accept/ sysctl is enabled,
but does not currently work for multihop sessions. Another approach is to
configure multiple BFD instances, one for each VRF (including the default VRF).
Each BFD instance associated with a VRF (regular or default) only handles
session requests from protocols in the same VRF.
<p>Some of BFD session options require <m/time/ value, which has to be specified
with the appropriate unit: <m/num/ <cf/s/|<cf/ms/|<cf/us/. Although microseconds
are allowed as units, practical minimum values are usually in order of tens of