BGP Configuration Guide

BGP is a standard exterior gateway protocol (EGP) supported by RtBrick. BGP is considered a “Path Vector” routing protocol and maintains a separate routing table based on shortest Autonomous system (AS) path and various other route attributes.

The RBFS supports the following BGP functions:

The statements and commands required to configure and verify the functioning of BGP features are described in this guide.

The address family configured at the instance level determines the types of address families that the virtual routing and forwarding (VRF) instance supports. At this level, you also configure the route target (RT), and the import and export policies for the instance. The forwarding daemon (FWDD) uses these configuration statements to create the VRF tables for each address family. Note that the route distinguisher (RD) is configured under the instance hierarchy level.

At the BGP protocol level, the address family configuration is used to determine which address families BGP supports. Multiple commands exist under this hierarchy level.

At the BGP peer group level, the address family configuration is used to determine which address families are needed to negotiate usage with the other BGP peers in the group.

There is no configuration under the peer hierarchy level. This statement establishes the peer, and all peers must be associated with a peer group. All of the parameters that apply to a peer are determined at the peer-group hierarchy level.

For example, this sequence configures IPv4 unicast support for the vrf1 instance:

BGP determines support for route redistribution based on address family. The selected address family can redistribute local interface routes, static routes, routes learned by IS-IS, and so on. Complete redistribute statement information and examples are included in other sections.

Configure and log into the RBFS instance

Configure the route distinguisher (RD) to define unique routes within an IPv4 network. Provider Edge (PE) routers use route distinguishers to identify which virtual private network (VPN) a packet belongs to in a PE network.

Configure the route target (RT) to use to transfer routes between VRFs and VPNs. The RT identifies a subset of routes within the BGP VPNv3 unicast table that should be used in a VRF for a particular customer. You configure an RT for importing or exporting routes, or both.

You must enable BGP inside an instance before you configure the BGP-specific instance options. When this enable command is successfully executed, the mode is changed from edit to set.

edit protocol bgp

You must configure the BGP address families if you are using route redistribution, load balancing, or other advanced features. By default, BGP neighbor sessions support IP4v unicast and multicast address families.

In addition to the basic family support, you can also configure a number of options.

Supported options, detailed in sections below, are:

This statement is for temporary use until full routing policy support is configured. Use this statement to configure the number of prefixes that the BGP unicast session can download to the forwarding daemon (FWDD). BGP downloads the attribute information (community, extended community, and as-path) for prefixes to the Routing Information Base (RIB) and Forwarding Information Base (FIB) for advertising.

You can assign counters based on BGP prefixes and attributes on a per-input interface basis.

set protocol bgp address-family <address-family-afi> <address-family-safi> unicast download-count <count-number>

Apply the BGP routing policy for downloaded routes. The policy is defined elsewhere.

set protocol bgp address-family <address-family-afi> <address-family-safi> download-policy <policy-name>

Allow load sharing among the configured number of multiple Exterior BGP (EBGP) and Internal BGP (IBGP) paths.

Enable the redistribution feature to dynamically inject routes from a certain protocol into the IP routing table.

By default, the forwarding table retains the VPN routes for all route targets when the roputing protocol process shuts down. If you disable this retention of route targets, the VPN routes are removed from the forwarding table when the routing protocol shuts down.

set instance <instance> protocol bgp address-family <address-family-afi> <address-family-safi> retain-route-target disable

The Segment Routing Global Block (SRGB) is the range of label values reserved for segment routing (SR). These values are assigned as segment identifiers (SIDs) to SR-enabled network nodes and have global significance throughout the routing domain.

You must specify the base starting value for the labels (a number greater than 15), a range for the labels, and an index within the label range.

Configure cluster ID to associate routers in a group within a BGP routing instance. Routers belong to the same cluster if they have the same cluster ID. The cluster ID is formatted as an IPv4 address.

set instance <instance> protocol bgp cluster-id <cluster-identifier>

Configure the domain name for this BGP routing instance.

By default, the BGP routing process enforces the First AS feature. This feature discards updates received from an eBGP peer if the peer does not list its own AS number as the first segment in the AS_PATH BGP attribute.

To disable the First AS feature and accept updates without the peer’s source AS matching the first AS in the AS_PATH attribute, configure the feature to disable the enforce First AS feature.

set instance <instance> protocol bgp enforce-first-as disable

Configure a host name for BGP to use.

Configure the local AS number in four-byte format for BGP to use.

set instance <instance> protocol bgp local-as <as4-number>

Configure the value to use as BGP local preference. You can use the local AS preference number to choose the exit path for an AS.

set instance <instance> protocol bgp local-preference <preference-number>

Configure the value to use as BGP Multi-Exit Discriminator (MED) value. When an AS has multiple links to another AS, the MED value is used to determine the exit to use to reach the other AS.

Assign a protocol preference distance value to routes learned by eBGP, iBGP, or both.

Configure the value used as the router ID.

set instance <instance> protocol bgp router-id <router-id>

Configure the timer value used to keep the router active.

set instance <instance> protocol bgp timer hold-time <seconds>

set instance <instance> protocol bgp timer keep-alive <seconds>

Configure the value for the type-of-service (DSCP) bits.

set instance <instance> protocol bgp type-of-service cost <low|normal>

set instance <instance> protocol bgp type-of-service delay <low|normal>

set instance <instance> protocol bgp type-of-service precedence <precedence>

set instance <instance> protocol bgp type-of-service reliability <high|normal>

set instance <instance> protocol bgp type-of-service throughput <high|normal>

Configure a name for a peer group of BGP routers. Neighbor peers with the same update policies can be grouped as peers (equals) to simplify the initial configuration and updates. Peers share the same policies such as route maps, distribution lists, filter lists, update source, and so on, so peer groups only need one configuration statement for these values.

set instance <instance> protocol bgp peer-group <peer-group-name> ( address-family <address-family-afi> | any-as <true|false> | ebgp-multihop <hop-count> | link-local-nexthop-only <true|false> | local-as <as-number> | remote-as <as-number>)

You must configure the BGP address families for a peer-group if you are using route redistribution, load balancing, or other advanced features. Note: The advanced features are NOT configured here, but under the BGP instance. By default, BGP neighbor sessions support IP4v unicast and multicast address families.

set instance <instance> protocol bgp peer-group <peer-group-name> address-family <address-family-afi> <address-family-safi> [ options ]

Configure parameters for a, IPv4 or IPv6 BGP peer. A BGP peer is a BGP router that has an active TCP connection to another BGP router. To establish point-to-point connections between peer autonomous systems (ASs) for eBGP or within the AS for iBGP, you configure a BGP session on an interface. When you configure a BGP peer, the configuration adds the IP address of the peer in the specified autonomous system to the multiprotocol BGP (mBPG) neighbor table maintained in the local router.

set instance <instance> protocol bgp peer ( ipv4 | ipv6) <peer-address> <update-source> peer-group <peer-group-name>

There are three main peer types to configure:

Each type has a general peer configuration format associated with it:

Display information about the BGP routing information base local (rib-local) table for an address family. The rib-local table is used to determine entries for the forwarding table.

show bgp rib <afi> <safi>

Display information summary about the BGP routes downloaded to the Forwarding Information Base (FIB) table.

show bgp rib <afi> <safi>

Display information summary about the BGP routes in the peer group table that will be sent to peers from the Routing Information Base output (RIB-out) table.

show bgp rib <peer-group-name> <afi> <safi>

Display information summary about the BGP peers.

show bgp peer ( instance <instance-name> )

Display detailed information about the BGP peers.

show bgp peer <peer-ip> detail ( instance <instance-name> )

Display information summary about the RIB-in table and a peer.

show bgp peer <peer-ip> rib-in <afi> <safi>

Routing Policies are the rules that allows you to control and modify the default behaviour of the routing protocols such as BGP and IS-IS. To use routing policies, you configure policies, and then apply policies to peer groups or instances.

RtBrick supports attaching a BGP routing policy at two levels:

In each case, you can apply the policy as an import or export policy and filter. As expected, import filters determine which routing updates are accepted and export filters determine which routes are advertised to other peers.

An import policy, when applied to an address family at the peer group level, examines all incoming routes from all BGP peers in the peer group, but only for that address family.

An export policy, when applied to an address family at the peer group level, examines all outgoing routes to all BGP peers in the peer group. but only for that address family.

At the instance level, routing policies that are applied to an address family can work as import or export policies, but for the instance as a whole.

An import policy, when applied to an address family at the instance level, examines all incoming routes before accepting the information only from global or default tables to other instance or VRF table.

An export policy, when applied to an address family at the instance level, examines all outgoing routes before sending the information from the VRF to global, and then to the vpn table (default).

Policies are useful when they are applied to routes, and for policies to be applied to routes they need to be made known to routing protocols. In BGP, for example, there are several situations where policies can be used, the most common of these is defining import and export policy. The policy attachment point is the point in which an association is formed between a specific protocol entity, in this case a BGP neighbor, and a specific named policy.

Export policies attached to a BGP peer-group, can be used to apply certain conditions based on any of the route attributes and advertise to the peers, only those route that match our criteria.

Import policies attached to a BGP peer-group, can be used to filter and modify based on any of the route attribute that we wish to.

Export policies attached to an instance, help us to modify the attributes of a route present in the instance before exporting them as VPN routes. If we would to attach an extended_community, nexthop, community etc before exporting them as VPN routes, we can do so by using this attachment point.

Import policies attached to an instance, help us to modify the attributes of a route/route-list before importing into the instance. The matching criteria can be any of the route attributes such as prefix, as_path, community, extended_community etc.

The following sections show a few examples of useful routing policies for BGP.

These examples show only the basics of the complete application of routing policy. Almost all BGP attributes can be used, along with many possible keywords. The current list is as follows:

Note: When one of the parameters such as source-port, destination-port, source-ip or destination-ip is matched, the authentication will be successful