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Update bgp.rst

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Add some commands to Route Selection section;
Add Administrative Distance configuration section;
Add Network Advertisement configuration;
Add Peers configuration section;
Add Timers configuration
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@ -174,6 +174,13 @@ ASN and Router ID
Route Selection
---------------
.. cfgcmd:: set protocols bgp <asn> parameters always-compare-med
This command provides to compare the MED on routes, even when they were
received from different neighbouring ASes. Setting this option makes the
order of preference of routes more defined, and should eliminate MED
induced oscillations.
.. cfgcmd:: set protocols bgp <asn> parameters bestpath as-path confed
This command specifies that the length of confederation path sets and
@ -190,6 +197,254 @@ Route Selection
Ignore AS_PATH length when selecting a route
.. cfgcmd:: set protocols bgp <asn> parameters bestpath compare-routerid
Ensure that when comparing routes where both are equal on most metrics,
including local-pref, AS_PATH length, IGP cost, MED, that the tie is
broken based on router-ID.
If this option is enabled, then the already-selected check, where
already selected eBGP routes are preferred, is skipped.
If a route has an ORIGINATOR_ID attribute because it has been reflected,
that ORIGINATOR_ID will be used. Otherwise, the router-ID of the peer
the route was received from will be used.
The advantage of this is that the route-selection (at this point) will
be more deterministic. The disadvantage is that a few or even one lowest-ID
router may attract all traffic to otherwise-equal paths because of this
check. It may increase the possibility of MED or IGP oscillation, unless
other measures were taken to avoid these. The exact behaviour will be
sensitive to the iBGP and reflection topology.
.. cfgcmd:: set protocols bgp <asn> parameters bestpath med confed
This command specifies that BGP considers the MED when comparing routes
originated from different sub-ASs within the confederation to which this
BGP speaker belongs. The default state, where the MED attribute is not
considered.
.. cfgcmd:: set protocols bgp <asn> parameters bestpath med missing-as-worst
This command specifies that a route with a MED is always considered to be
better than a route without a MED by causing the missing MED attribute to
have a value of infinity. The default state, where the missing MED
attribute is considered to have a value of zero.
.. cfgcmd:: set protocols bgp <asn> parameters default local-pref <local-pref value>
This command specifies the default local preference value. The local
preference range is 0 to 4294967295.
.. cfgcmd:: set protocols bgp <asn> parameters default no-ipv4-unicast
This command allows the user to specify that IPv4 peering is turned off by
default.
.. cfgcmd:: set protocols bgp <asn> parameters deterministic-med
This command provides to compare different MED values that advertised by
neighbours in the same AS for routes selection. When this command is enabled,
routes from the same autonomous system are grouped together, and the best
entries of each group are compared.
Administrative Distance
-----------------------
.. cfgcmd:: set protocols bgp <asn> parameters distance global <external|internal|local> <distance>
This command change distance value of BGP. The arguments are the distance
values for external routes, internal routes and local routes respectively.
The distance range is 1 to 255.
.. cfgcmd:: set protocols bgp <asn> parameters distance prefix <subnet> distance <distance>
This command sets the administrative distance for a particular route. The
distance range is 1 to 255.
.. note:: Routes with a distance of 255 are effectively disabled and not
installed into the kernel.
Network Advertisement
---------------------
.. cfgcmd:: set protocols bgp <asn> address-family <ipv4-unicast|ipv6-unicast> network <prefix>
This command is used for advertising IPv4 or IPv6 networks.
.. note:: By default, the BGP prefix is advertised even if it's not
present in the routing table. This behaviour differs from the
implementation of some vendors.
.. cfgcmd:: set protocols bgp <asn> parameters network-import-check
This configuration modifies the behavior of the network statement.
If you have this configured the underlying network must exist in the rib
Peers
-----
Defining Peers
^^^^^^^^^^^^^^
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> remote-as <nasn>
This command creates a new neighbor whose remote-as is NASN. The neighbor
address can be an IPv4 address or an IPv6 address or an interface to use
for the connection.
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> remote-as internal
Create a peer as you would when you specify an ASN, except that if the
peers ASN is different than mine as specified under the :cfgcmd:`protocols
bgp <asn>` command the connection will be denied.
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> remote-as external
Create a peer as you would when you specify an ASN, except that if the
peers ASN is the same as mine as specified under the :cfgcmd:`protocols
bgp <asn>` command the connection will be denied.
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> shutdown
This command disable the peer. To reenable the peer use the delete
form of this command.
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> description <text>
Set description of the peer.
Capability Negotiation
^^^^^^^^^^^^^^^^^^^^^^
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> capability dynamic
This command would allow the dynamic update of capabilities over an
established BGP session.
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> capability extended-nexthop
Allow bgp to negotiate the extended-nexthop capability with it’s peer.
If you are peering over a IPv6 Link-Local address then this capability
is turned on automatically. If you are peering over a IPv6 Global Address
then turning on this command will allow BGP to install IPv4 routes with
IPv6 nexthops if you do not have IPv4 configured on interfaces.
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> disable-capability-negotiation
Suppress sending Capability Negotiation as OPEN message optional
parameter to the peer. This command only affects the peer is
configured other than IPv4 unicast configuration.
When remote peer does not have capability negotiation feature,
remote peer will not send any capabilities at all. In that case,
bgp configures the peer with configured capabilities.
You may prefer locally configured capabilities more than the negotiated
capabilities even though remote peer sends capabilities. If the peer is
configured by :cfgcmd:`override-capability`, VyOS ignores received capabilities
then override negotiated capabilities with configured values.
Additionally you should keep in mind that this feature fundamentally
disables the ability to use widely deployed BGP features. BGP unnumbered,
hostname support, AS4, Addpath, Route Refresh, ORF, Dynamic Capabilities,
and graceful restart.
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> override-capability
This command allow override the result of Capability Negotiation with
local configuration. Ignore remote peer’s capability value.
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> strict-capability-match
This command forces strictly compare remote capabilities and local
capabilities. If capabilities are different, send Unsupported Capability
error then reset connection.
You may want to disable sending Capability Negotiation OPEN message
optional parameter to the peer when remote peer does not implement
Capability Negotiation. Please use :cfgcmd:`disable-capability-negotiation`
command to disable the feature.
Peer Parameters
^^^^^^^^^^^^^^^
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> address-family <ipv4-unicast|ipv6-unicast> allowas-in number <number>
This command accept incoming routes with AS path containing AS
number with the same value as the current system AS. This is
used when you want to use the same AS number in your sites,
but you can’t connect them directly.
The number parameter (1-10) configures the amount of accepted
occurences of the system AS number in AS path.
This command is only allowed for eBGP peers.
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> address-family <ipv4-unicast|ipv6-unicast> as-override
This command override AS number of the originating router with
the local AS number.
Usually this configuration is used in PEs (Provider Edge) to
replace the incoming customer AS number so the connected CE (
Customer Edge) can use the same AS number as the other customer
sites. This allows customers of the provider network to use the
same AS number across their sites.
This command is only allowed for eBGP peers.
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> address-family <ipv4-unicast|ipv6-unicast> attribute-unchanged <as-path|med|next-hop>
This command specifies attributes to be left unchanged for
advertisements sent to a peer.
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> address-family <ipv4-unicast|ipv6-unicast> maximum-prefix <number>
This command specifies a maximum number of prefixes we can receive
from a given peer. If this number is exceeded, the BGP session
will be destroyed. The number range is 1 to 4294967295.
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> address-family <ipv4-unicast|ipv6-unicast> nexthop-self
This command forces the BGP speaker to report itself as the
next hop for an advertised route it advertised to a neighbor.
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> address-family <ipv4-unicast|ipv6-unicast> remove-private-as
This command removes the private ASN of routes that are advertised
to the configured peer. It removes only private ASNs on routes
advertised to EBGP peers.
If the AS-Path for the route has only private ASNs, the private
ASNs are removed.
If the AS-Path for the route has a private ASN between public
ASNs, it is assumed that this is a design choice, and the
private ASN is not removed.
.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> address-family <ipv4-unicast|ipv6-unicast> weight <number>
This command specifies a default weight value for the neighbor’s
routes. The number range is 1 to 65535.
Timers
------
.. cfgcmd:: set protocols bgp <asn> timers holdtime <seconds>
This command specifies hold-time in seconds. The timer can
range from 4 to 65535.The default value is 180 second. If
you set value to 0 VyOS will not hold routes.
.. cfgcmd:: set protocols bgp <asn> timers keepalive <seconds>
This command specifies keep-alive time in seconds. The timer
can range from 4 to 65535.The default value is 60 second.
Configuration Examples
----------------------
IPv4
^^^^