BGP Router ConfigurationΒΆ

This statement enters BGP server mode for the specified VRF and enters config-bgp mode.

tnsr(config)# route dynamic bgp
tnsr(config-frr-bgp)# server vrf default


Older versions of TNSR specified the ASN here, rather than a VRF name. That format has been deprecated. The ASN is still mandatory, but is now set by the as-number <asn> command within config-bgp mode.

BGP mode defines the main behaviors of the BGP daemon, as well as the neighbors and behavior of BGP for different address families, among other possibilities.

From within config-bgp mode, the following commands are available:

as-number <asn>

Mandatory. Sets the autonomous system number for this BGP instance.

address-family (ipv4|ipv6) (unicast|multicast)

Enter BGP Address Family Configuration mode.


Instructs the BGP daemon to always consult MED values in routes, no matter which AS the routes were received through.

bestpath as-path (confed|ignore|multipath-relax|as-set|no-as-set)

Controls how the BGP daemon determines the best path to a destination. May be one of:


Considers the length of confederation path sets and sequences.


Ignores AS path lengths when computing the route to a destination.


Consider paths of equal length when choosing between multiple paths to a destination, rather than looking for an exact match. This allows load sharing across different AS paths, so long as they are of equal length.


For use with multipath-relax, it adds AS set information for aggregate routes.


For use with multipath-relax, it prevents AS set generation.

bestpath compare-routerid

Uses the router ID of peers (or originator ID, if present) to break ties when computing paths to a destination based on other information. A lower router ID will win in a tie.

bestpath med confed

Compare confederation path MEDs

bestpath med missing-as-worst

If a route is missing MED information, it will be considered least preferred.

client-to-client reflection

Enables reflection of routes from one client to another client.

cluster-id (<ipv4>|<value>)

Configures the BGP daemon to participate in route reflection with the given cluster ID. The ID may be given in IP address (dotted quad) notation or as an unsigned 32-bit integer (1-4294967295).

coalesce-time <value>

Configures the Subgroup coalesce timer, in milliseconds (1-4294967295).

confederation identifier <ASN>

Configures an AS number for the entire group of IBGP routers participating in confederation.

confederation peer <ASN>

Configures the sub-AS number for the subset of peers inside a group of IBGP routers participating in confederation.

dampening [penalty <val> [reuse <val> [suppress <val> [maximum <max>]]]]

This command enables BGP route flap dampening (RFC 2439) to prevent unstable routers from adversely affecting routing behavior.

penalty <penalty-val>

The time duration during which the stability value will be reduced by half if the route is unreachable.

reuse <reuse-val>

Stability threshold that must be crossed for a route to be reused.

suppress <suppress-val>

Stability threshold that, when crossed, a route will be suppressed.

maximum <suppress-max>

Maximum time to suppress a route considered stable.


Determine route selection locally, even when MED values are present. Picks the best MED path from neighbor advertisements.


Disable checking if nexthop is an eBGP session.


Controls whether or not BGP will advertise IPv4 unicast routes. By default, BGP will advertise both IPv4 and IPv6 unicast routes. Using no with this command will limit BGP such that it only advertises IPv6 unicast routes.

listen limit <value>

Maximum number of dynamic neighbors from 1-5000.

listen range (<ip4-prefix>|<ip6-prefix>) peer-group <peer-group-name>

Listen range for dynamic neighbors.

max-med administrative [<med>]

Sends the defined MED value, or 4294967294 when unset, at all times.

max-med on-startup period <seconds> [<med>]

Sends the defined MED value, or 4294967294 when unset, only at startup for the defined period in seconds, from 5-86400.

neighbor <peer>

Enter BGP Neighbor Configuration mode.

network import-check

Checks if a BGP network route exists in IGP before creating BGP table entries.

route-reflector allow-outbound-policy

Allows attributes modified by route maps to be reflected.

router-id <A.B.C.D>

Sets the router ID for the BGP daemon. This is typically set to an IP address unique to this router, and commonly is set to a local private address.

timers keep-alive <interval> hold-time <hold-time>

Configures the intervals between keep alive messages and how long to wait for a response before considering the peer unreachable.

update-delay <delay>

Keeps BGP in a read-only mode for the specified time after the daemon restarts or peers are cleared.

write-quanta <packets>

Controls the size of peer update transmissions.