.. _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 AS 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 :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. .. _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. .. _bgp-router-configuration: BGP Router Configuration ======================== ASN and Router ID ----------------- .. cfgcmd:: set protocols bgp 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. .. cfgcmd:: set protocols bgp parameters router-id This command specifies the router-ID. If router ID is not specified it will use the highest interface IP address. Route Selection --------------- .. 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 This command specifies the default local preference value. The local preference range is 0 to 4294967295. .. 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 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 parameters distance global 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 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 address-family network 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 rib Peers ----- Defining Peers ^^^^^^^^^^^^^^ .. cfgcmd:: set protocols bgp neighbor remote-as 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 neighbor 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 ` command the connection will be denied. .. cfgcmd:: set protocols bgp neighbor 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 ` command the connection will be denied. .. cfgcmd:: set protocols bgp neighbor shutdown This command disable the peer. To reenable the peer use the delete form of this command. .. cfgcmd:: set protocols bgp neighbor description Set description of the peer. Capability Negotiation ^^^^^^^^^^^^^^^^^^^^^^ .. cfgcmd:: set protocols bgp neighbor capability dynamic This command would allow the dynamic update of capabilities over an established BGP session. .. cfgcmd:: set protocols bgp neighbor 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 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 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 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-family allowas-in 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 neighbor address-family 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-family attribute-unchanged This command specifies attributes to be left unchanged for advertisements sent to a peer. .. cfgcmd:: set protocols bgp neighbor address-family maximum-prefix 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-family 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-family 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-family weight This command specifies a default weight value for the neighbor’s routes. The number range is 1 to 65535. Timers ------ .. cfgcmd:: set protocols bgp timers holdtime 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 timers keepalive 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 ^^^^ A simple eBGP configuration: **Node 1:** .. code-block:: none set protocols bgp 65534 neighbor 192.168.0.2 ebgp-multihop '2' set protocols bgp 65534 neighbor 192.168.0.2 remote-as '65535' set protocols bgp 65534 neighbor 192.168.0.2 update-source '192.168.0.1' set protocols bgp 65534 address-family ipv4-unicast network '172.16.0.0/16' set protocols bgp 65534 parameters router-id '192.168.0.1' **Node 2:** .. code-block:: none set protocols bgp 65535 neighbor 192.168.0.1 ebgp-multihop '2' set protocols bgp 65535 neighbor 192.168.0.1 remote-as '65534' set protocols bgp 65535 neighbor 192.168.0.1 update-source '192.168.0.2' set protocols bgp 65535 address-family ipv4-unicast network '172.17.0.0/16' set protocols bgp 65535 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 ^^^^ A simple BGP configuration via IPv6. **Node 1:** .. code-block:: none set protocols bgp 65534 neighbor 2001:db8::2 ebgp-multihop '2' set protocols bgp 65534 neighbor 2001:db8::2 remote-as '65535' set protocols bgp 65534 neighbor 2001:db8::2 update-source '2001:db8::1' set protocols bgp 65534 neighbor 2001:db8::2 address-family ipv6-unicast set protocols bgp 65534 address-family ipv6-unicast network '2001:db8:1::/48' set protocols bgp 65534 parameters router-id '10.1.1.1' **Node 2:** .. code-block:: none set protocols bgp 65535 neighbor 2001:db8::1 ebgp-multihop '2' set protocols bgp 65535 neighbor 2001:db8::1 remote-as '65534' set protocols bgp 65535 neighbor 2001:db8::1 update-source '2001:db8::2' set protocols bgp 65535 neighbor 2001:db8::1 address-family ipv6-unicast set protocols bgp 65535 address-family ipv6-unicast network '2001:db8:2::/48' set protocols bgp 65535 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 Filter ^^^^^^^^^^^^ 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 65534 neighbor 2001:db8::2 address-family ipv4-unicast route-map export 'AS65535-OUT' set protocols bgp 65534 neighbor 2001:db8::2 address-family ipv4-unicast route-map import 'AS65535-IN' set protocols bgp 65534 neighbor 2001:db8::2 address-family ipv6-unicast route-map export 'AS65535-OUT' set protocols bgp 65534 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 65535 neighbor 2001:db8::1 address-family ipv4-unicast route-map export 'AS65534-OUT' set protocols bgp 65535 neighbor 2001:db8::1 address-family ipv4-unicast route-map import 'AS65534-IN' set protocols bgp 65535 neighbor 2001:db8::1 address-family ipv6-unicast route-map export 'AS65534-OUT' set protocols bgp 65535 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.