From 8943fc9f877cbee3301a8261ddd27b4b1f15f174 Mon Sep 17 00:00:00 2001 From: rebortg Date: Mon, 30 Nov 2020 20:53:36 +0100 Subject: arrange services and protocols --- docs/configuration/protocols/bgp.rst | 335 +++++++++++++++++++++++++++++++++++ 1 file changed, 335 insertions(+) create mode 100644 docs/configuration/protocols/bgp.rst (limited to 'docs/configuration/protocols/bgp.rst') diff --git a/docs/configuration/protocols/bgp.rst b/docs/configuration/protocols/bgp.rst new file mode 100644 index 00000000..c576d836 --- /dev/null +++ b/docs/configuration/protocols/bgp.rst @@ -0,0 +1,335 @@ +.. _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 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 + +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. -- cgit v1.2.3