gated BGP protocol statement

   bgp yes|no|on|off [ {
       [preference preference ;]
       [defaultmetric metric ;]
       [traceoptions traceoptions ;]
       [group type external|internal|igp|test peeras peeras
           [metricout metric]
           [localas localas]
           [nogendefault]
           [gateway gateway]
           [preference preference]
           [lcladdr local_address]
           [holdtime time]
           [traceoptions traceoptions]
           [version version]
           [passive]
           [importdefault]
           [exportdefault]
           [sendbuffer bufsize]
           [recvbuffer bufsize]
           [spoolbuffer bufsize]
           [keepall]
           {
               [allow { dest_mask . . . } ;]
               [peer host
                   [metricout metric]
                   [localas localas]
                   [nogendefault]
                   [gateway gateway]
                   [preference preference]
                   [lcladdr local_address]
                   [holdtime time]
                   [traceoptions traceoptions]
                   [version version]
                   [passive]
                   [importdefault]
                   [exportdefault]
                   [sendbuffer bufsize]
                   [recvbuffer bufsize]
                   [spoolbuffer bufsize]
                   [keepall]
                  ;]
                  . . .
           } ;
       . . .]
   } ] ;

preference preference

Sets the preference for routes learned from BGP. The default preference is 170. This preference may be overridden by a preference specified on the group or peer statements or by import policy.

defaultmetric metric

Defines the metric used when advertising routes via BGP. If not specified, no metric is propagated. This metric may be overridden by a metric specified in the neighbor or group statements or in export policy.

traceoptions traceoptions

Specifies the tracing options for BGP. By default, these are inherited from the global trace options. These values may be overridden on a group or neighbor basis. (See ``gated trace statements'').

group type external peeras autonomous_system

In the classic external BGP group, full policy checking is applied to all incoming and outgoing advertisements. The external neighbors must be directly reachable through one of the machine's local interfaces. By default no metric is included in external advertisements and the next hop is computed with respect to the shared interface.

group type internal peeras autonomous_system

This is an internal group operating where there is no IP-level igp; for example, an SMDS network or MILnet. All neighbors in this group are required to be directly reachable via a single interface. All next hop information is computed with respect to this interface. Import and export policy may be applied to group advertisements. Routes received from external BGP or EGP neighbors are, by default, readvertised with the received metric.

group type igp peeras autonomous_system

---

NOTE: ``igp '' as used in the above line is a keyword. ``igp'' as used in the following paragraph represents one or more unspecific hosts running an internal routing protocol. In the latter case, ``igp'' stands for internal gateway protocol.) This is an internal group that runs in association with an interior protocol. The igp group examines routes that the igp is exporting and sends an advertisement only if the path attributes could not be entirely represented in the igp tag mechanism. Only the AS path, path origin, and transitive optional attributes are sent with routes. No metric is sent, and the next hop is set to the local address used by the connection. Received internal BGP routes are not used or readvertised. Instead, the AS path information is attached to the corresponding igp route and the latter is used for readvertisement. Since internal igp peers are sent only a subset of the routes that the igp is exporting, the export policy used is the that of the igp. There is no need to implement the "don't route from peers in the same group" constraint since the advertised routes are routes that igp already exports.

---

group type test peeras autonomous_system

This is an extension to an external BGP group that implements a fixed policy using test peers. Fixed policy and special case code make test peers relatively inexpensive to maintain. Test peers do not need to be on a directly attached network. If gated and the peer are on the same (directly attached) subnet, the advertised next hop is computed with respect to that network; otherwise, the next hop is the local machine's current next hop. All routing information advertised by and received from a test peer is discarded, and all BGP routes that may be advertised are sent back to the test peer. Metrics from EGP- and BGP-derived routes are forwarded in the advertisement; otherwise, no metric is included.

Within a group, BGP peers may be configured in one of two ways. They may be explicitly configured with a peer statement or implicitly configured with the allow clause. Both are described following.

allow

The allow clause allows for peer connections from any addresses in the specified set of address masks. All parameters for these peers must be configured in the group clause. The internal peer structures are created when an incoming open request is received and destroyed when the connection is broken. For more detail on specifying the network/mask pairs, see ``gated route filtering''.

peer host

A peer clause configures an individual peer. Each peer inherits all parameters specified on a group as defaults. Those defaults may be overridden by parameters explicitly specified on the peer subclause.

The BGP peer subclause allows the following parameters, which can also be specified in the group clause. All are optional.

metricout metric

If specified, this metric is used as the primary metric on all routes sent to the specified peer(s). This metric overrides the default metric, a metric specified in the group, and any metric specified by export policy.

localas localas

Identifies the autonomous system that gated is representing to this group of peers. The default is that which has been set globally in the autonomoussystem statement.

nogendefault

Prevents gated from generating a default route when BGP receives a valid update from its neighbor. The default route is generated only when the gendefault option is enabled.

gateway gateway

If a network is not shared with a peer, gateway specifies a router on an attached network to be used as the next hop router for routes received from this neighbor. This parameter is not needed in most cases.

preference preference

Specifies the preference used for routes learned from these peers. This can differ from the default BGP preference set in the bgp statement, so that gated can prefer routes from one peer, or group of peers, over others. This preference may be explicitly overridden by import policy.

lcladdr local_address

Specifies the address to be used on the local end of the TCP connection with the peer. For external peers, the local address must be on an interface that is shared with the peer or with the peer's gateway when the gateway parameter is used. A session with an external peer will only be opened when an interface with the appropriate local address (through which the peer or gateway address is directly reachable) is operating. For other types of peer, a peer session will be maintained when any interface with the specified local address is operating. In either case incoming connections will only be recognized as matching a configured peer if they are addressed to the configured local address.

holdtime time

Specifies the BGP holdtime value to use when negotiating the connection with this peer, in seconds. According to BGP, if gated does not receive a keepalive, update, or notification message within the period specified in the Hold Time field of the BGP OPEN message, then the BGP connection will be closed. The value must be either 0 (no keepalives will be sent) or at least 3.

version version

Specifies the version of the BGP protocol to use with this peer. If not specified, the highest supported version is used first and version negotiation is attempted. If it is specified, only the specified version will be offered during negotiation. Currently supported versions are 2 and 3.

passive

Specifies that active OPENs to this peer should not be attempted. gated should wait for the peer to issue an OPEN. By default, all explicitly configured peers are active; they periodically send OPEN messages until the peer responds.

sendbuffer bufsize
recvbuffer bufsize

Control the amount of send and receive buffering asked of the kernel. The maximum supported is 65535 bytes although many kernels have a lower limit. By default, gated configures the maximum supported. These parameters are not needed on normally functioning systems.

keepall

Used to retain routes learned from a peer even if the routes' AS paths contain one of the exported AS numbers.

traceoptions traceoptions

Specifies the tracing options for this BGP neighbor. By default, these are inherited from group or BGP global trace options. (See ``gated trace statements'').