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vyos-documentation/docs/configuration/protocols/bgp.rst
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.. _routing-bgp:
###
BGP
###
:abbr:`BGP (Border Gateway Protocol)` is one of the Exterior Gateway Protocols
and the de facto standard interdomain routing protocol. The latest BGP version
is 4. BGP-4 is described in :rfc:`1771` and updated by :rfc:`4271`. :rfc:`2858`
adds multiprotocol support to BGP.
VyOS makes use of :abbr:`FRR (Free Range Routing)` and we would like to thank
them for their effort!
**************
Basic Concepts
**************
.. _bgp-autonomous-systems:
Autonomous Systems
==================
From :rfc:`1930`:
An AS is a connected group of one or more IP prefixes run by one or more
network operators which has a SINGLE and CLEARLY DEFINED routing policy.
Each :abbr:`AS (Autonomous System)` has an identifying number associated with it
called an :abbr:`ASN (Autonomous System Number)`. This is a two octet value
ranging in value from 1 to 65535. The AS numbers 64512 through 65535 are defined
as private AS numbers. Private AS numbers must not be advertised on the global
Internet. The 2-byte AS number range has been exhausted. 4-byte AS numbers are
specified in :rfc:`6793`, and provide a pool of 4294967296 AS numbers.
The :abbr:`ASN (Autonomous System Number)` is one of the essential elements of
BGP. BGP is a distance vector routing protocol, and the AS-Path framework
provides distance vector metric and loop detection to BGP.
.. cfgcmd:: set protocols bgp local-as <asn>
Set local :abbr:`ASN (Autonomous System Number)` that this router represents.
This is a a mandatory option!
.. _bgp-address-families:
Address Families
================
Multiprotocol extensions enable BGP to carry routing information for multiple
network layer protocols. BGP supports an Address Family Identifier (AFI) for
IPv4 and IPv6.
.. _bgp-route-selection:
Route Selection
===============
The route selection process used by FRR's BGP implementation uses the following
decision criterion, starting at the top of the list and going towards the
bottom until one of the factors can be used.
1. **Weight check**
Prefer higher local weight routes to lower routes.
2. **Local preference check**
Prefer higher local preference routes to lower.
3. **Local route check**
Prefer local routes (statics, aggregates, redistributed) to received routes.
4. **AS path length check**
Prefer shortest hop-count AS_PATHs.
5. **Origin check**
Prefer the lowest origin type route. That is, prefer IGP origin routes to
EGP, to Incomplete routes.
6. **MED check**
Where routes with a MED were received from the same AS, prefer the route
with the lowest MED.
7. **External check**
Prefer the route received from an external, eBGP peer over routes received
from other types of peers.
8. **IGP cost check**
Prefer the route with the lower IGP cost.
9. **Multi-path check**
If multi-pathing is enabled, then check whether the routes not yet
distinguished in preference may be considered equal. If
:cfgcmd:`bgp bestpath as-path multipath-relax` is set, all such routes are
considered equal, otherwise routes received via iBGP with identical AS_PATHs
or routes received from eBGP neighbours in the same AS are considered equal.
10. **Already-selected external check**
Where both routes were received from eBGP peers, then prefer the route
which is already selected. Note that this check is not applied if
:cfgcmd:`bgp bestpath compare-routerid` is configured. This check can
prevent some cases of oscillation.
11. **Router-ID check**
Prefer the route with the lowest `router-ID`. If the route has an
`ORIGINATOR_ID` attribute, through iBGP reflection, then that router ID is
used, otherwise the `router-ID` of the peer the route was received from is
used.
12. **Cluster-List length check**
The route with the shortest cluster-list length is used. The cluster-list
reflects the iBGP reflection path the route has taken.
13. **Peer address**
Prefer the route received from the peer with the higher transport layer
address, as a last-resort tie-breaker.
.. _bgp-capability-negotiation:
Capability Negotiation
======================
When adding IPv6 routing information exchange feature to BGP. There were some
proposals. :abbr:`IETF (Internet Engineering Task Force)`
:abbr:`IDR (Inter Domain Routing)` adopted a proposal called Multiprotocol
Extension for BGP. The specification is described in :rfc:`2283`. The protocol
does not define new protocols. It defines new attributes to existing BGP. When
it is used exchanging IPv6 routing information it is called BGP-4+. When it is
used for exchanging multicast routing information it is called MBGP.
*bgpd* supports Multiprotocol Extension for BGP. So if a remote peer supports
the protocol, *bgpd* can exchange IPv6 and/or multicast routing information.
Traditional BGP did not have the feature to detect a remote peer's
capabilities, e.g. whether it can handle prefix types other than IPv4 unicast
routes. This was a big problem using Multiprotocol Extension for BGP in an
operational network. :rfc:`2842` adopted a feature called Capability
Negotiation. *bgpd* use this Capability Negotiation to detect the remote peer's
capabilities. If a peer is only configured as an IPv4 unicast neighbor, *bgpd*
does not send these Capability Negotiation packets (at least not unless other
optional BGP features require capability negotiation).
By default, FRR will bring up peering with minimal common capability for the
both sides. For example, if the local router has unicast and multicast
capabilities and the remote router only has unicast capability the local router
will establish the connection with unicast only capability. When there are no
common capabilities, FRR sends Unsupported Capability error and then resets the
connection.
*************
Configuration
*************
.. _bgp-router-configuration:
BGP Router Configuration
========================
First of all you must configure BGP router with the :abbr:`ASN (Autonomous
System Number)`. The AS number is an identifier for the autonomous system.
The BGP protocol uses the AS number for detecting whether the BGP connection
is internal or external. VyOS does not have a special command to start the BGP
process. The BGP process starts when the first neighbor is configured.
.. cfgcmd:: set protocols bgp local-as <asn>
Set local autonomous system number that this router represents. This is a
a mandatory option!
Peers Configuration
-------------------
Defining Peers
^^^^^^^^^^^^^^
.. cfgcmd:: set protocols bgp 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. The command is applicable for peer and peer group.
.. cfgcmd:: set protocols bgp 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 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 neighbor <address|interface> shutdown
This command disable the peer or peer group. To reenable the peer use
the delete form of this command.
.. cfgcmd:: set protocols bgp neighbor <address|interface> description
<text>
Set description of the peer or peer group.
.. cfgcmd:: set protocols bgp neighbor <address|interface> update-source
<address|interface>
Specify the IPv4 source address to use for the BGP session to this neighbor,
may be specified as either an IPv4 address directly or as an interface name.
.. _bgp_capability_negotiation:
Capability Negotiation
^^^^^^^^^^^^^^^^^^^^^^
.. cfgcmd:: set protocols bgp neighbor <address|interface> capability
dynamic
This command would allow the dynamic update of capabilities over an
established BGP session.
.. cfgcmd:: set protocols bgp 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 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 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 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 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. It is not applicable
for peer groups.
.. cfgcmd:: set protocols bgp 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 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 or peer group.
.. cfgcmd:: set protocols bgp 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 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 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 neighbor <address|interface> address-family
<ipv4-unicast|ipv6-unicast> soft-reconfiguration inbound
Changes in BGP policies require the BGP session to be cleared. Clearing has a
large negative impact on network operations. Soft reconfiguration enables you
to generate inbound updates from a neighbor, change and activate BGP policies
without clearing the BGP session.
This command specifies that route updates received from this neighbor will be
stored unmodified, regardless of the inbound policy. When inbound soft
reconfiguration is enabled, the stored updates are processed by the new
policy configuration to create new inbound updates.
.. note:: Storage of route updates uses memory. If you enable soft
reconfiguration inbound for multiple neighbors, the amount of memory used
can become significant.
.. cfgcmd:: set protocols bgp 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.
.. cfgcmd:: set protocols bgp neighbor <address|interface>
advertisement-interval <seconds>
This command specifies the minimum route advertisement interval for
the peer. The interval value is 0 to 600 seconds, with the default
advertisement interval being 0.
.. cfgcmd:: set protocols bgp neighbor <address|interface>
disable-connected-check
This command allows peerings between directly connected eBGP peers
using loopback addresses without adjusting the default TTL of 1.
.. cfgcmd:: set protocols bgp neighbor <address|interface>
disable-send-community <extended|standard>
This command specifies that the community attribute should not be sent
in route updates to a peer. By default community attribute is sent.
.. cfgcmd:: set protocols bgp neighbor <address|interface> ebgp-multihop
<number>
This command allows sessions to be established with eBGP neighbors
when they are multiple hops away. When the neighbor is not directly
connected and this knob is not enabled, the session will not establish.
The number of hops range is 1 to 255. This command is mutually
exclusive with :cfgcmd:`ttl-security hops`.
.. cfgcmd:: set protocols bgp neighbor <address|interface> local-as <asn>
[no-prepend] [replace-as]
Specify an alternate AS for this BGP process when interacting with
the specified peer or peer group. With no modifiers, the specified
local-as is prepended to the received AS_PATH when receiving routing
updates from the peer, and prepended to the outgoing AS_PATH (after
the process local AS) when transmitting local routes to the peer.
If the :cfgcmd:`no-prepend` attribute is specified, then the supplied
local-as is not prepended to the received AS_PATH.
If the :cfgcmd:`replace-as` attribute is specified, then only the supplied
local-as is prepended to the AS_PATH when transmitting local-route
updates to this peer.
.. note:: This command is only allowed for eBGP peers.
.. cfgcmd:: set protocols bgp neighbor <address|interface> passive
Configures the BGP speaker so that it only accepts inbound connections
from, but does not initiate outbound connections to the peer or peer group.
.. cfgcmd:: set protocols bgp neighbor <address|interface> password
<text>
This command specifies a MD5 password to be used with the tcp socket that
is being used to connect to the remote peer.
.. cfgcmd:: set protocols bgp neighbor <address|interface> ttl-security
hops <number>
This command enforces Generalized TTL Security Mechanism (GTSM),
as specified in :rfc:`5082`. With this command, only neighbors
that are the specified number of hops away will be allowed to
become neighbors. The number of hops range is 1 to 254. This
command is mutually exclusive with :cfgcmd:`ebgp-multihop`.
Peer Groups
^^^^^^^^^^^
Peer groups are used to help improve scaling by generating the same update
information to all members of a peer group. Note that this means that the
routes generated by a member of a peer group will be sent back to that
originating peer with the originator identifier attribute set to indicated
the originating peer. All peers not associated with a specific peer group
are treated as belonging to a default peer group, and will share updates.
.. cfgcmd:: set protocols bgp peer-group <name>
This command defines a new peer group. You can specify to the group the same
parameters that you can specify for specific neighbors.
.. note:: If you apply a parameter to an individual neighbor IP address, you
override the action defined for a peer group that includes that IP
address.
.. cfgcmd:: set protocols bgp neighbor <address|interface> peer-group
<name>
This command bind specific peer to peer group with a given name.
Network Advertisement Configuration
-----------------------------------
.. cfgcmd:: set protocols bgp 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 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 routing table.
.. cfgcmd:: set protocols bgp neighbor <address|interface> address-family
<ipv4-unicast|ipv6-unicast> default-originate [route-map <name>]
By default, VyOS does not advertise a default route (0.0.0.0/0) even if it is
in routing table. When you want to announce default routes to the peer, use
this command. Using optional argument :cfgcmd:`route-map` you can inject the
default route to given neighbor only if the conditions in the route map are
met.
Route Aggregation Configuration
-------------------------------
.. cfgcmd:: set protocols bgp address-family <ipv4-unicast|ipv6-unicast>
aggregate-address <prefix>
This command specifies an aggregate address. The router will also
announce longer-prefixes inside of the aggregate address.
.. cfgcmd:: set protocols bgp address-family <ipv4-unicast|ipv6-unicast>
aggregate-address <prefix> as-set
This command specifies an aggregate address with a mathematical set of
autonomous systems. This command summarizes the AS_PATH attributes of
all the individual routes.
.. cfgcmd:: set protocols bgp address-family <ipv4-unicast|ipv6-unicast>
aggregate-address <prefix> summary-only
This command specifies an aggregate address and provides that
longer-prefixes inside of the aggregate address are suppressed
before sending BGP updates out to peers.
.. cfgcmd:: set protocols bgp neighbor <address|interface> address-family
<ipv4-unicast|ipv6-unicast> unsuppress-map <name>
This command applies route-map to selectively unsuppress prefixes
suppressed by summarisation.
Redistribution Configuration
----------------------------
.. cfgcmd:: set protocols bgp address-family <ipv4-unicast|ipv6-unicast>
redistribute <route source>
This command redistributes routing information from the given route source
to the BGP process. There are six modes available for route source:
connected, kernel, ospf, rip, static, table.
.. cfgcmd:: set protocols bgp address-family <ipv4-unicast|ipv6-unicast>
redistribute <route source> metric <number>
This command specifies metric (MED) for redistributed routes. The
metric range is 0 to 4294967295. There are six modes available for
route source: connected, kernel, ospf, rip, static, table.
.. cfgcmd:: set protocols bgp address-family <ipv4-unicast|ipv6-unicast>
redistribute <route source> route-map <name>
This command allows to use route map to filter redistributed routes.
There are six modes available for route source: connected, kernel,
ospf, rip, static, table.
General Configuration
---------------------
Common parameters
^^^^^^^^^^^^^^^^^
.. cfgcmd:: set protocols bgp parameters router-id <id>
This command specifies the router-ID. If router ID is not specified it will
use the highest interface IP address.
.. cfgcmd:: set protocols bgp maximum-paths <ebgp|ibgp> <number>
This command defines the maximum number of parallel routes that
the BGP can support. In order for BGP to use the second path, the
following attributes have to match: Weight, Local Preference, AS
Path (both AS number and AS path length), Origin code, MED, IGP
metric. Also, the next hop address for each path must be different.
.. cfgcmd:: set protocols bgp parameters default no-ipv4-unicast
This command allows the user to specify that IPv4 peering is turned off by
default.
.. cfgcmd:: set protocols bgp parameters log-neighbor-changes
This command enable logging neighbor up/down changes and reset reason.
.. cfgcmd:: set protocols bgp parameters no-client-to-client-reflection
This command disables route reflection between route reflector clients.
By default, the clients of a route reflector are not required to be
fully meshed and the routes from a client are reflected to other clients.
However, if the clients are fully meshed, route reflection is not required.
In this case, use the :cfgcmd:`no-client-to-client-reflection` command
to disable client-to-client reflection.
.. cfgcmd:: set protocols bgp parameters no-fast-external-failover
Disable immediate session reset if peer's connected link goes down.
.. cfgcmd:: set protocols bgp listen range <prefix> peer-group <name>
This command is useful if one desires to loosen the requirement for BGP
to have strictly defined neighbors. Specifically what is allowed is for
the local router to listen to a range of IPv4 or IPv6 addresses defined
by a prefix and to accept BGP open messages. When a TCP connection
(and subsequently a BGP open message) from within this range tries to
connect the local router then the local router will respond and connect
with the parameters that are defined within the peer group. One must define
a peer-group for each range that is listed. If no peer-group is defined
then an error will keep you from committing the configuration.
.. cfgcmd:: set protocols bgp listen limit <number>
This command goes hand in hand with the listen range command to limit the
amount of BGP neighbors that are allowed to connect to the local router.
The limit range is 1 to 5000.
.. cfgcmd:: set protocols bgp parameters ebgp-requires-policy
This command changes the eBGP behavior of FRR. By default FRR enables
:rfc:`8212` functionality which affects how eBGP routes are advertised,
namely no routes are advertised across eBGP sessions without some
sort of egress route-map/policy in place. In VyOS however we have this
RFC functionality disabled by default so that we can preserve backwards
compatibility with older versions of VyOS. With this option one can
enable :rfc:`8212` functionality to operate.
Administrative Distance
^^^^^^^^^^^^^^^^^^^^^^^
.. cfgcmd:: set protocols bgp 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 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.
Timers
^^^^^^
.. cfgcmd:: set protocols bgp timers holdtime <seconds>
This command specifies hold-time in seconds. The timer range is
4 to 65535. The default value is 180 second. If you set value to 0
VyOS will not hold routes.
.. cfgcmd:: set protocols bgp 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.
Route Dampening
^^^^^^^^^^^^^^^
When a route fails, a routing update is sent to withdraw the route from the
network's routing tables. When the route is re-enabled, the change in
availability is also advertised. A route that continually fails and returns
requires a great deal of network traffic to update the network about the
route's status.
Route dampening wich described in :rfc:`2439` enables you to identify routes
that repeatedly fail and return. If route dampening is enabled, an unstable
route accumulates penalties each time the route fails and returns. If the
accumulated penalties exceed a threshold, the route is no longer advertised.
This is route suppression. Routes that have been suppressed are re-entered
into the routing table only when the amount of their penalty falls below a
threshold.
A penalty of 1000 is assessed each time the route fails. When the penalties
reach a predefined threshold (suppress-value), the router stops advertising
the route.
Once a route is assessed a penalty, the penalty is decreased by half each time
a predefined amount of time elapses (half-life-time). When the accumulated
penalties fall below a predefined threshold (reuse-value), the route is
unsuppressed and added back into the BGP routing table.
No route is suppressed indefinitely. Maximum-suppress-time defines the maximum
time a route can be suppressed before it is re-advertised.
.. cfgcmd:: set protocols bgp parameters dampening
half-life <minutes>
This command defines the amount of time in minutes after
which a penalty is reduced by half. The timer range is
10 to 45 minutes.
.. cfgcmd:: set protocols bgp parameters dampening
re-use <seconds>
This command defines the accumulated penalty amount at which the
route is re-advertised. The penalty range is 1 to 20000.
.. cfgcmd:: set protocols bgp parameters dampening
start-suppress-time <seconds>
This command defines the accumulated penalty amount at which the
route is suppressed. The penalty range is 1 to 20000.
.. cfgcmd:: set protocols bgp parameters dampening
max-suppress-time <seconds>
This command defines the maximum time in minutes that a route is
suppressed. The timer range is 1 to 255 minutes.
Route Selection Configuration
-----------------------------
.. cfgcmd:: set protocols bgp 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 parameters bestpath as-path confed
This command specifies that the length of confederation path sets and
sequences should be taken into account during the BGP best path
decision process.
.. cfgcmd:: set protocols bgp parameters bestpath as-path multipath-relax
This command specifies that BGP decision process should consider paths
of equal AS_PATH length candidates for multipath computation. Without
the knob, the entire AS_PATH must match for multipath computation.
.. cfgcmd:: set protocols bgp parameters bestpath as-path ignore
Ignore AS_PATH length when selecting a route
.. cfgcmd:: set protocols bgp 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 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 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 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 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.
.. cfgcmd:: set protocols bgp address-family ipv4-unicast network
<prefix> backdoor
This command allows the router to prefer route to specified prefix learned
via IGP through backdoor link instead of a route to the same prefix learned
via EBGP.
Route Filtering Configuration
-----------------------------
In order to control and modify routing information that is exchanged between
peers you can use route-map, filter-list, prefix-list, distribute-list.
For inbound updates the order of preference is:
- route-map
- filter-list
- prefix-list, distribute-list
For outbound updates the order of preference is:
- prefix-list, distribute-list
- filter-list
- route-map
.. note:: The attributes :cfgcmd:`prefix-list` and :cfgcmd:`distribute-list`
are mutually exclusive, and only one command (distribute-list or
prefix-list) can be applied to each inbound or outbound direction for a
particular neighbor.
.. cfgcmd:: set protocols bgp neighbor <address|interface> address-family
<ipv4-unicast|ipv6-unicast> distribute-list <export|import> <number>
This command applies the access list filters named in <number> to the
specified BGP neighbor to restrict the routing information that BGP learns
and/or advertises. The arguments :cfgcmd:`export` and :cfgcmd:`import`
specify the direction in which the access list are applied.
.. cfgcmd:: set protocols bgp neighbor <address|interface> address-family
<ipv4-unicast|ipv6-unicast> prefix-list <export|import> <name>
This command applies the prfefix list filters named in <name> to the
specified BGP neighbor to restrict the routing information that BGP learns
and/or advertises. The arguments :cfgcmd:`export` and :cfgcmd:`import`
specify the direction in which the prefix list are applied.
.. cfgcmd:: set protocols bgp neighbor <address|interface> address-family
<ipv4-unicast|ipv6-unicast> route-map <export|import> <name>
This command applies the route map named in <name> to the specified BGP
neighbor to control and modify routing information that is exchanged
between peers. The arguments :cfgcmd:`export` and :cfgcmd:`import`
specify the direction in which the route map are applied.
.. cfgcmd:: set protocols bgp neighbor <address|interface> address-family
<ipv4-unicast|ipv6-unicast> filter-list <export|import> <name>
This command applies the AS path access list filters named in <name> to the
specified BGP neighbor to restrict the routing information that BGP learns
and/or advertises. The arguments :cfgcmd:`export` and :cfgcmd:`import`
specify the direction in which the AS path access list are applied.
.. cfgcmd:: set protocols bgp neighbor <address|interface> address-family
<ipv4-unicast|ipv6-unicast> capability orf <receive|send>
This command enables the ORF capability (described in :rfc:`5291`) on the
local router, and enables ORF capability advertisement to the specified BGP
peer. The :cfgcmd:`receive` keyword configures a router to advertise ORF
receive capabilities. The :cfgcmd:`send` keyword configures a router to
advertise ORF send capabilities. To advertise a filter from a sender, you
must create an IP prefix list for the specified BGP peer applied in inbound
derection.
BGP Scaling Configuration
-------------------------
BGP routers connected inside the same AS through BGP belong to an internal BGP
session, or IBGP. In order to prevent routing table loops, IBGP speaker does
not advertise IBGP-learned routes to other IBGP speaker (Split Horizon
mechanism). As such, IBGP requires a full mesh of all peers. For large
networks, this quickly becomes unscalable.
There are two ways that help us to mitigate the BGPs full-mesh requirement in
a network:
- Using BGP route-reflectors
- Using BGP confederation
Route Reflector Configuration
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Introducing route reflectors removes the need for the full-mesh. When you
configure a route reflector you have to tell the router whether the other IBGP
router is a client or non-client. A client is an IBGP router that the route
reflector will “reflect” routes to, the non-client is just a regular IBGP
neighbor. Route reflectors mechanism is described in :rfc:`4456` and updated
by :rfc:`7606`.
.. cfgcmd:: set protocols bgp neighbor <address> address-family
<ipv4-unicast|ipv6-unicast> route-reflector-client
This command specifies the given neighbor as route reflector client.
.. cfgcmd:: set protocols bgp parameters cluster-id <id>
This command specifies cluster ID which identifies a collection of route
reflectors and their clients, and is used by route reflectors to avoid
looping. By default cluster ID is set to the BGP router id value, but can be
set to an arbitrary 32-bit value.
Confederation Configuration
^^^^^^^^^^^^^^^^^^^^^^^^^^^
A BGP confederation divides our AS into sub-ASes to reduce the number of
required IBGP peerings. Within a sub-AS we still require full-mesh IBGP but
between these sub-ASes we use something that looks like EBGP but behaves like
IBGP (called confederation BGP). Confederation mechanism is described in
:rfc:`5065`
.. cfgcmd:: set protocols bgp parameters confederation identifier
<asn>
This command specifies a BGP confederation identifier. <asn> is the number
of the autonomous system that internally includes multiple sub-autonomous
systems (a confederation).
.. cfgcmd:: set protocols bgp parameters confederation confederation
peers <nsubasn>
This command sets other confederations <nsubasn> as members of autonomous
system specified by :cfgcmd:`confederation identifier <asn>`.
*************************
Operational Mode Commands
*************************
Show
====
.. opcmd:: show <ip|ipv6> bgp
This command displays all entries in BGP routing table.
.. code-block:: none
BGP table version is 10, local router ID is 10.0.35.3, vrf id 0
Default local pref 100, local AS 65000
Status codes: s suppressed, d damped, h history, * valid, > best, = multipath,
i internal, r RIB-failure, S Stale, R Removed
Nexthop codes: @NNN nexthop's vrf id, < announce-nh-self
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 198.51.100.0/24 10.0.34.4 0 0 65004 i
*> 203.0.113.0/24 10.0.35.5 0 0 65005 i
Displayed 2 routes and 2 total paths
.. opcmd:: show <ip|ipv6> bgp <address|prefix>
This command displays information about the particular entry in the BGP
routing table.
.. code-block:: none
BGP routing table entry for 198.51.100.0/24
Paths: (1 available, best #1, table default)
Advertised to non peer-group peers:
10.0.13.1 10.0.23.2 10.0.34.4 10.0.35.5
65004
10.0.34.4 from 10.0.34.4 (10.0.34.4)
Origin IGP, metric 0, valid, external, best (First path received)
Last update: Wed Jan 6 12:18:53 2021
.. opcmd:: show ip bgp cidr-only
This command displays routes with classless interdomain routing (CIDR).
.. opcmd:: show <ip|ipv6> bgp community <value>
This command displays routes that belong to specified BGP communities.
Valid value is a community number in the range from 1 to 4294967200,
or AA:NN (autonomous system-community number/2-byte number), no-export,
local-as, or no-advertise.
.. opcmd:: show <ip|ipv6> bgp community-list <name>
This command displays routes that are permitted by the BGP
community list.
.. opcmd:: show ip bgp dampened-paths
This command displays BGP dampened routes.
.. opcmd:: show ip bgp flap-statistics
This command displays information about flapping BGP routes.
.. opcmd:: show ip bgp filter-list <name>
This command displays BGP routes allowed by by the specified AS Path
access list.
.. opcmd:: show <ip|ipv6> bgp neighbors <address> advertised-routes
This command displays BGP routes advertised to a neighbor.
.. opcmd:: show <ip|ipv6> bgp neighbors <address> received-routes
This command displays BGP routes originating from the specified BGP
neighbor before inbound policy is applied. To use this command inbound
soft reconfiguration must be enabled.
.. opcmd:: show <ip|ipv6> bgp neighbors <address> routes
This command displays BGP received-routes that are accepted after filtering.
.. opcmd:: show <ip|ipv6> bgp neighbors <address> dampened-routes
This command displays dampened routes received from BGP neighbor.
.. opcmd:: show <ip|ipv6> bgp regexp <text>
This command displays information about BGP routes whose AS path
matches the specified regular expression.
.. opcmd:: show <ip|ipv6> bgp summary
This command displays the status of all BGP connections.
.. code-block:: none
IPv4 Unicast Summary:
BGP router identifier 10.0.35.3, local AS number 65000 vrf-id 0
BGP table version 11
RIB entries 5, using 920 bytes of memory
Peers 4, using 82 KiB of memory
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
10.0.13.1 4 65000 148 159 0 0 0 02:16:01 0
10.0.23.2 4 65000 136 143 0 0 0 02:13:21 0
10.0.34.4 4 65004 161 163 0 0 0 02:16:01 1
10.0.35.5 4 65005 162 166 0 0 0 02:16:01 1
Total number of neighbors 4
Reset
=====
.. opcmd:: reset <ip|ipv6> bgp <address> [soft [in|out]]
This command resets BGP connections to the specified neighbor IP address.
With argument :cfgcmd:`soft` this command initiates a soft reset. If
you do not specify the :cfgcmd:`in` or :cfgcmd:`out` options, both
inbound and outbound soft reconfiguration are triggered.
.. opcmd:: reset ip bgp all
This command resets all BGP connections of given router.
.. opcmd:: reset ip bgp dampening
This command uses to clear BGP route dampening information and to
unsuppress suppressed routes.
.. opcmd:: reset ip bgp external
This command resets all external BGP peers of given router.
.. opcmd:: reset ip bgp peer-group <name> [soft [in|out]]
This command resets BGP connections to the specified peer group.
With argument :cfgcmd:`soft` this command initiates a soft reset. If
you do not specify the :cfgcmd:`in` or :cfgcmd:`out` options, both
inbound and outbound soft reconfiguration are triggered.
********
Examples
********
IPv4 peering
============
A simple eBGP configuration:
**Node 1:**
.. code-block:: none
set protocols bgp local-as 65534
set protocols bgp neighbor 192.168.0.2 ebgp-multihop '2'
set protocols bgp neighbor 192.168.0.2 remote-as '65535'
set protocols bgp neighbor 192.168.0.2 update-source '192.168.0.1'
set protocols bgp address-family ipv4-unicast network '172.16.0.0/16'
set protocols bgp parameters router-id '192.168.0.1'
**Node 2:**
.. code-block:: none
set protocols bgp local-as 65535
set protocols bgp neighbor 192.168.0.1 ebgp-multihop '2'
set protocols bgp neighbor 192.168.0.1 remote-as '65534'
set protocols bgp neighbor 192.168.0.1 update-source '192.168.0.2'
set protocols bgp address-family ipv4-unicast network '172.17.0.0/16'
set protocols bgp parameters router-id '192.168.0.2'
Don't forget, the CIDR declared in the network statement MUST **exist in your
routing table (dynamic or static), the best way to make sure that is true is
creating a static route:**
**Node 1:**
.. code-block:: none
set protocols static route 172.16.0.0/16 blackhole distance '254'
**Node 2:**
.. code-block:: none
set protocols static route 172.17.0.0/16 blackhole distance '254'
IPv6 peering
============
A simple BGP configuration via IPv6.
**Node 1:**
.. code-block:: none
set protocols bgp local-as 65534
set protocols bgp neighbor 2001:db8::2 ebgp-multihop '2'
set protocols bgp neighbor 2001:db8::2 remote-as '65535'
set protocols bgp neighbor 2001:db8::2 update-source '2001:db8::1'
set protocols bgp neighbor 2001:db8::2 address-family ipv6-unicast
set protocols bgp address-family ipv6-unicast network '2001:db8:1::/48'
set protocols bgp parameters router-id '10.1.1.1'
**Node 2:**
.. code-block:: none
set protocols bgp local-as 65535
set protocols bgp neighbor 2001:db8::1 ebgp-multihop '2'
set protocols bgp neighbor 2001:db8::1 remote-as '65534'
set protocols bgp neighbor 2001:db8::1 update-source '2001:db8::2'
set protocols bgp neighbor 2001:db8::1 address-family ipv6-unicast
set protocols bgp address-family ipv6-unicast network '2001:db8:2::/48'
set protocols bgp parameters router-id '10.1.1.2'
Don't forget, the CIDR declared in the network statement **MUST exist in your
routing table (dynamic or static), the best way to make sure that is true is
creating a static route:**
**Node 1:**
.. code-block:: none
set protocols static route6 2001:db8:1::/48 blackhole distance '254'
**Node 2:**
.. code-block:: none
set protocols static route6 2001:db8:2::/48 blackhole distance '254'
Route Filtering
===============
Route filter can be applied using a route-map:
**Node1:**
.. code-block:: none
set policy prefix-list AS65535-IN rule 10 action 'permit'
set policy prefix-list AS65535-IN rule 10 prefix '172.16.0.0/16'
set policy prefix-list AS65535-OUT rule 10 action 'deny'
set policy prefix-list AS65535-OUT rule 10 prefix '172.16.0.0/16'
set policy prefix-list6 AS65535-IN rule 10 action 'permit'
set policy prefix-list6 AS65535-IN rule 10 prefix '2001:db8:2::/48'
set policy prefix-list6 AS65535-OUT rule 10 action 'deny'
set policy prefix-list6 AS65535-OUT rule 10 prefix '2001:db8:2::/48'
set policy route-map AS65535-IN rule 10 action 'permit'
set policy route-map AS65535-IN rule 10 match ip address prefix-list 'AS65535-IN'
set policy route-map AS65535-IN rule 10 match ipv6 address prefix-list 'AS65535-IN'
set policy route-map AS65535-IN rule 20 action 'deny'
set policy route-map AS65535-OUT rule 10 action 'deny'
set policy route-map AS65535-OUT rule 10 match ip address prefix-list 'AS65535-OUT'
set policy route-map AS65535-OUT rule 10 match ipv6 address prefix-list 'AS65535-OUT'
set policy route-map AS65535-OUT rule 20 action 'permit'
set protocols bgp local-as 65534
set protocols bgp neighbor 2001:db8::2 address-family ipv4-unicast route-map export 'AS65535-OUT'
set protocols bgp neighbor 2001:db8::2 address-family ipv4-unicast route-map import 'AS65535-IN'
set protocols bgp neighbor 2001:db8::2 address-family ipv6-unicast route-map export 'AS65535-OUT'
set protocols bgp neighbor 2001:db8::2 address-family ipv6-unicast route-map import 'AS65535-IN'
**Node2:**
.. code-block:: none
set policy prefix-list AS65534-IN rule 10 action 'permit'
set policy prefix-list AS65534-IN rule 10 prefix '172.17.0.0/16'
set policy prefix-list AS65534-OUT rule 10 action 'deny'
set policy prefix-list AS65534-OUT rule 10 prefix '172.17.0.0/16'
set policy prefix-list6 AS65534-IN rule 10 action 'permit'
set policy prefix-list6 AS65534-IN rule 10 prefix '2001:db8:1::/48'
set policy prefix-list6 AS65534-OUT rule 10 action 'deny'
set policy prefix-list6 AS65534-OUT rule 10 prefix '2001:db8:1::/48'
set policy route-map AS65534-IN rule 10 action 'permit'
set policy route-map AS65534-IN rule 10 match ip address prefix-list 'AS65534-IN'
set policy route-map AS65534-IN rule 10 match ipv6 address prefix-list 'AS65534-IN'
set policy route-map AS65534-IN rule 20 action 'deny'
set policy route-map AS65534-OUT rule 10 action 'deny'
set policy route-map AS65534-OUT rule 10 match ip address prefix-list 'AS65534-OUT'
set policy route-map AS65534-OUT rule 10 match ipv6 address prefix-list 'AS65534-OUT'
set policy route-map AS65534-OUT rule 20 action 'permit'
set protocols bgp local-as 65535
set protocols bgp neighbor 2001:db8::1 address-family ipv4-unicast route-map export 'AS65534-OUT'
set protocols bgp neighbor 2001:db8::1 address-family ipv4-unicast route-map import 'AS65534-IN'
set protocols bgp neighbor 2001:db8::1 address-family ipv6-unicast route-map export 'AS65534-OUT'
set protocols bgp neighbor 2001:db8::1 address-family ipv6-unicast route-map import 'AS65534-IN'
We could expand on this and also deny link local and multicast in the rule 20
action deny.
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