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| -rw-r--r-- | docs/configuration/protocols/bgp.rst | 633 |
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diff --git a/docs/configuration/protocols/bgp.rst b/docs/configuration/protocols/bgp.rst index ae7eb795..27858224 100644 --- a/docs/configuration/protocols/bgp.rst +++ b/docs/configuration/protocols/bgp.rst @@ -28,7 +28,9 @@ From :rfc:`1930`: 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. +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 @@ -156,200 +158,11 @@ connection. BGP Router Configuration ======================== -ASN and Router ID ------------------ - -.. cfgcmd:: set protocols bgp <asn> - - 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 <asn> 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 <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 - sequences should be taken into account during the BGP best path - decision process. - -.. cfgcmd:: set protocols bgp <asn> 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 <asn> parameters bestpath as-path ignore - - 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 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 routing table. - -.. cfgcmd:: set protocols bgp <asn> 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 ------------------ - -.. cfgcmd:: set protocols bgp <asn> 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 <asn> 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 <asn> 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. - -Redistribution --------------- - -.. cfgcmd:: set protocols bgp <asn> address-family <ipv4-unicast|ipv6-unicast> - redistribute connected - - Redistribute connected routes to BGP process. - -.. cfgcmd:: set protocols bgp <asn> address-family <ipv4-unicast|ipv6-unicast> - redistribute kernel - - Redistribute kernel routes to BGP process. - -.. cfgcmd:: set protocols bgp <asn> address-family <ipv4-unicast|ipv6-unicast> - redistribute ospf - - Redistribute OSPF routes to BGP process. - -.. cfgcmd:: set protocols bgp <asn> address-family <ipv4-unicast|ipv6-unicast> - redistribute rip - - Redistribute RIP routes to BGP process. - -.. cfgcmd:: set protocols bgp <asn> address-family <ipv4-unicast|ipv6-unicast> - redistribute static - - Redistribute static routes to BGP process. - -.. cfgcmd:: set protocols bgp <asn> 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. - -.. cfgcmd:: set protocols bgp <asn> address-family <ipv4-unicast|ipv6-unicast> - redistribute <route source> route-map <name> - - This command allows to use route map to filter redistributed routes. +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. Peers Configuration ------------------- @@ -360,7 +173,7 @@ 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 + 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 it applicable for peer and peer group. @@ -368,7 +181,7 @@ Defining Peers 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 + 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 @@ -391,9 +204,10 @@ Defining Peers .. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> update-source <address|interface> - Specify the IPv4 source address to use for the BGP session to this neighbour, + 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. + Capability Negotiation ^^^^^^^^^^^^^^^^^^^^^^ @@ -451,6 +265,7 @@ Capability Negotiation Capability Negotiation. Please use :cfgcmd:`disable-capability-negotiation` command to disable the feature. + Peer Parameters ^^^^^^^^^^^^^^^ @@ -489,22 +304,6 @@ Peer Parameters advertisements sent to a peer or peer group. .. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> address-family - <ipv4-unicast|ipv6-unicast> distribute-list <export|import> <number> - - This command applys 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 prefix lists are applied. - -.. cfgcmd:: set protocols bgp <asn> neighbor <address|interface> address-family - <ipv4-unicast|ipv6-unicast> filter-list <export|import> <name> - - This command applys 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 prefix lists are applied. - -.. 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 @@ -566,6 +365,12 @@ Peer Parameters This command allows peerings between directly connected eBGP peers using loopback addresses without adjusting the default TTL of 1. + +.. cfgcmd:: set protocols bgp <asn> 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 <asn> neighbor <address|interface> ebgp-multihop <number> @@ -598,6 +403,12 @@ Peer Parameters 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 <asn> 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 <asn> neighbor <address|interface> ttl-security hops <number> @@ -608,6 +419,7 @@ Peer Parameters become neighbors. The number of hops range is 1 to 254. This command is mutually exclusive with :cfgcmd:`ebgp-multihop`. + Peer Groups ^^^^^^^^^^^ @@ -632,9 +444,100 @@ are treated as belonging to a default peer group, and will share updates. This command bind specific peer to peer group with a given name. -General configuration + +Network Advertisement Configuration +----------------------------------- + +.. 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 routing table. + +.. cfgcmd:: set protocols bgp <asn> 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 <asn> 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 <asn> 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 <asn> 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 <asn> 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 <asn> 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: bgp, + connected, kernel, ospf, rip, static. + +.. cfgcmd:: set protocols bgp <asn> 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: bgp, connected, kernel, ospf, rip, static. + +.. cfgcmd:: set protocols bgp <asn> 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: bgp, connected, kernel, + ospf, rip, static. + + +General Configuration --------------------- +Common parametrs +^^^^^^^^^^^^^^^^ + +.. cfgcmd:: set protocols bgp <asn> 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 <asn> maximum-paths <ebgp|ibgp> <number> This command defines the maximum number of parallel routes that @@ -657,38 +560,278 @@ General configuration Tis 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 + 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 <asn> parameters no-fast-external-failover Disable immediate sesison reset if peer's connected link goes down. + +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. + + 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. + 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 <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. + can range from 4 to 65535. The default value is 60 second. -Route Reflector Configuration + +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 <asn> 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 <asn> 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 <asn> 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 <asn> 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 <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 + sequences should be taken into account during the BGP best path + decision process. + +.. cfgcmd:: set protocols bgp <asn> 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 <asn> parameters bestpath as-path ignore + + 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 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 <asn> 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 <asn> neighbor <address|interface> address-family + <ipv4-unicast|ipv6-unicast> distribute-list <export|import> <number> + + This command applys 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 <asn> neighbor <address|interface> address-family + <ipv4-unicast|ipv6-unicast> prefix-list <export|import> <name> + + This command applys 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 <asn> neighbor <address|interface> address-family + <ipv4-unicast|ipv6-unicast> route-map <export|import> <name> + + This command applys 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 <asn> neighbor <address|interface> address-family + <ipv4-unicast|ipv6-unicast> filter-list <export|import> <name> + + This command applys 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 <asn> 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. Introducing route reflectors removes the need for -the full-mesh. Route reflectors mechanism is described in :rfc:`4456` and -updated by :rfc:`7606`. +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 <asn> neighbor <address> address-family <ipv4-unicast|ipv6-unicast> route-reflector-client @@ -703,6 +846,30 @@ updated by :rfc:`7606`. 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 <subasn> 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). <subasn> is the number sub-autonomous system + inside <asn>. + +.. cfgcmd:: set protocols bgp <subasn> 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 ========================= @@ -764,6 +931,15 @@ Show 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. @@ -837,6 +1013,7 @@ Reset you do not specify the :cfgcmd:`in` or :cfgcmd:`out` options, both inbound and outbound soft reconfiguration are triggered. + Configuration Examples ---------------------- |