BGP neighbor route-reflector-client

BGP Route Reflection: An Alternative to Full Mesh Internal BGP (IBGP)

Typically, all BGP speakers within a single AS must be fully meshed and any external routing information must be re-distributed to all other routers within that AS. For n BGP speakers within an AS that requires to maintain n*(n-1)/2 unique Internal BGP (IBGP) sessions. This "full mesh" requirement clearly does not scale when there are a large number of IBGP speakers each exchanging a large volume of routing information, as is common in many of today's networks. Use the neighbor route-reflector-client command to configure the local router as the route reflector and the specified neighbor as one of its clients. All the neighbors configured with this command will be members of the client group and the remaining iBGP peers will be members of the nonclient group for the local route reflector.

NOTE: BGP route reflectors relax the prohibition on advertising internally learned routes to other iBGP peers, but dividing peers into two separate classes of peers: route-reflector clients and non-clients, which are regular iBGP peers with the restrictions intact. Routes learned from clients will be advertised to other clients and to non-clients. However, routes learned from non-clients will be advertised only to the clients. This situation opens up interesting loop and failure scenarios that may need special handling.

Video Demonstration

from: Cisco IOS IP Routing: BGP Command Reference

neighbor route-reflector-client

To configure the router as a BGP route reflector and configure the specified neighbor as its client, use the neighbor route-reflector-client command in address family or router configuration mode. To indicate that the neighbor is not a client, use the no form of this command.

neighbor {ip-address | ipv6-address | peer-group-name} route-reflector-client

no neighbor {ip-address | ipv6-address | peer-group-name} route-reflector-client

Syntax Description

ip-address	IP address of the BGP neighbor being identified as a client.
ipv6-address	IPv6 address of the BGP neighbor being identified as a client.
peer-group-name	Name of a BGP peer group.

Command Default

There is no route reflector in the autonomous system.

Command Modes

Address family configuration (config-router-af)
Router configuration (config-router)

Command History

Release	Modification
11.1	This command was introduced.
12.0(7)T	Address family configuration mode was added.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2(33)SRB	The ipv6-address and peer-group-name arguments were added.
12.2(33)SB	This command was integrated into Cisco IOS Release 12.2(33)SB.
12.2(33)SXI	This command was integrated into Cisco IOS Release 12.2(33)SXI.
Cisco IOS XE Release 3.1S	This command was updated. It was integrated into Cisco IOS XE Release 3.1S.

Usage Guidelines

By default, all internal BGP (iBGP) speakers in an autonomous system must be fully meshed, and neighbors do not readvertise iBGP learned routes to neighbors, thus preventing a routing information loop. When all the clients are disabled, the local router is no longer a route reflector.

If you use route reflectors, all iBGP speakers need not be fully meshed. In the route reflector model, an Interior BGP peer is configured to be aroute reflector responsible for passing iBGP learned routes to iBGP neighbors. This scheme eliminates the need for each router to talk to every other router.

Use the neighbor route-reflector-client command to configure the local router as the route reflector and the specified neighbor as one of its clients. All the neighbors configured with this command will be members of the client group and the remaining iBGP peers will be members of the nonclient group for the local route reflector.

The bgp client-to-client reflection command controls client-to-client reflection.

Files:
Topology
Configs
BGP Configuration

BGP neighbor next-hop-self

When peering is done via the external network of a BGP edge router within an AS, a BGP edge router will not change the next hop of for the route from the advertising AS when it receives it but rather will pass it on unchanged to its IBGP neighbors.

Setting the next-hop-self parameter on each of the edge router’s IBGP connections, ensures a reachable next hop without increasing the size of the IGP table. The next-hop-self command will allow us to force BGP, to use a specified IP address as the next hop rather than letting the protocol choose the nexthop.

Video Demonstration

from: Cisco IOS IP Routing: BGP Command Reference

neighbor next-hop-self

To configure the router as the next hop for a BGP-speaking neighbor or peer group, use the neighbor next-hop-self command in router configuration mode. To disable this feature, use the no form of this command.

neighbor {ip-address | peer-group-name} next-hop-self

no neighbor {ip-address | peer-group-name} next-hop-self

Syntax Description

ip-address	IP address of the BGP-speaking neighbor.
peer-group-name	Name of a BGP peer group.

Defaults

This command is disabled by default.

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.
11.0	The peer-group-name argument was added.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.

Usage Guidelines

This command is useful in unmeshed networks (such as Frame Relay or X.25) where BGP neighbors may not have direct access to all other neighbors on the same IP subnet.

If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group will inherit the characteristic configured with this command. Specifying the command with an IP address will override the value inherited from the peer group.

For a finer granularity of control, see the set ip next-hop command.

Examples

The following example forces all updates destined for 10.108.1.1 to advertise this router as the next hop:

router bgp 109

 neighbor 10.108.1.1 next-hop-self

Related Commands

Command	Description
neighbor peer-group (creating)	Creates a BGP peer group.
set ip next-hop (BGP)	Indicates where to output packets that pass a match clause of a route map for policy routing.

Files:
Topology
Configs
BGP Configuration

BGP neighbor peer-group

A BGP peer group is a group of neighbors with the same update policies (as defined by route-maps, distribute-lists, filter-lists, etc). Instead of configuring each neighbor individually, peer groups enable you to group the neighbors together and define configuration options for all the members of the group. If you modify the options set in a peer group, all the members of the peer group inherit the changes. You can configure individual members to override those options that do not effect outbound updates.

These options can include:
remote-as, version, update-source, out-route-map, out-filter-list, out-distribution-list, next-hop-self, and minimum-advertisement-interval.

Video Demonstration

from: Cisco IOS IP Routing: BGP Command Reference

neighbor peer-group (assigning members)

To configure a BGP neighbor to be a member of a peer group, use the neighbor peer-group command in address family or router configuration mode. To remove the neighbor from the peer group, use the no form of this command.

neighbor {ip-address | ipv6-address} peer-group peer-group-name

no neighbor {ip-address | ipv6-address} peer-group peer-group-name

Syntax Description

ip-address	IP address of the BGP neighbor that belongs to the peer group specified by the peer-group-name argument.
ipv6-address	IPv6 address of the BGP neighbor that belongs to the peer group specified by the peer-group-name argument.
peer-group-name	Name of the BGP peer group to which this neighbor belongs.

Defaults

There are no BGP neighbors in a peer group.

Command Modes

Address family
Router configuration

Command History

Release	Modification
11.0	This command was introduced.
12.0(7)T	Address family configuration mode was added.
12.2(2)T	Support for IPv6 was added.
12.2(25)SG	This command was integrated into Cisco IOS Release 12.2(25)SG.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
Cisco IOS XE Release 2.1	This command was introduced on Cisco ASR 1000 Series Routers.

Usage Guidelines

The neighbor at the IP address indicated inherits all the configured options of the peer group.

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Note Using the no form of the neighbor peer-group command removes all of the BGP configuration for that neighbor, not just the peer group association.

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Examples

The following router configuration mode example assigns three neighbors to the peer group named internal:

router bgp 100

 neighbor internal peer-group

 neighbor internal remote-as 100

 neighbor internal update-source loopback 0

 neighbor internal route-map set-med out

 neighbor internal filter-list 1 out

 neighbor internal filter-list 2 in

 neighbor 172.16.232.53 peer-group internal

 neighbor 172.16.232.54 peer-group internal

 neighbor 172.16.232.55 peer-group internal

 neighbor 172.16.232.55 filter-list 3 in

The following address family configuration mode example assigns three neighbors to the peer group named internal:

router bgp 100

address-family ipv4 unicast

 neighbor internal peer-group

 neighbor internal remote-as 100

 neighbor internal update-source loopback 0

 neighbor internal route-map set-med out

 neighbor internal filter-list 1 out

 neighbor internal filter-list 2 in

 neighbor 172.16.232.53 peer-group internal

 neighbor 172.16.232.54 peer-group internal

 neighbor 172.16.232.55 peer-group internal

 neighbor 172.16.232.55 filter-list 3 in

Related Commands

Command	Description
address-family ipv4 (BGP)	Places the router in address family configuration mode for configuring routing sessions such as BGP, RIP, or static routing sessions that use standard IPv4 address prefixes.
address-family vpnv4	Places the router in address family configuration mode for configuring routing sessions such as BGP, RIP, or static routing sessions that use standard VPNv4 address prefixes.
neighbor peer-group (creating)	Creates a BGP peer group.
neighbor shutdown	Disables a neighbor or peer group.

neighbor peer-group (creating)

To create a BGP or multiprotocol BGP peer group, use the neighbor peer-group command in address family or router configuration mode. To remove the peer group and all of its members, use the no form of this command.

neighbor peer-group-name peer-group

no neighbor peer-group-name peer-group

Syntax Description

peer-group-name

Name of the BGP peer group.

Defaults

There is no BGP peer group.

Command Modes

Router configuration

Command History

Release	Modification
11.0	This command was introduced.
11.1(20)CC	The nlri unicast, nlri multicast, and nlri unicast multicast keywords were added.
12.0(2)S	The nlri unicast, nlri multicast, and nlri unicast multicast keywords were added.
12.0(7)T	The nlri unicast, nlri multicast, and nlri unicast multicast keywords were removed. Address family configuration mode was added.
12.2(25)SG	This command was integrated into Cisco IOS Release 12.2(25)SG.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.

Usage Guidelines

Often in a BGP or multiprotocol BGP speaker, many neighbors are configured with the same update policies (that is, same outbound route maps, distribute lists, filter lists, update source, and so on). Neighbors with the same update policies can be grouped into peer groups to simplify configuration and make update calculation more efficient.

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Note Peer group members can span multiple logical IP subnets, and can transmit, or pass along, routes from one peer group member to another.

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Once a peer group is created with the neighbor peer-group command, it can be configured with the neighbor commands. By default, members of the peer group inherit all the configuration options of the peer group. Members also can be configured to override the options that do not affect outbound updates.

All the peer group members will inherit the current configuration as well as changes made to the peer group. Peer group members will always inherit the following configuration options by default:

•remote-as (if configured)

•version

•update-source

•outbound route-maps

•outbound filter-lists

•outbound distribute-lists

•minimum-advertisement-interval

•next-hop-self

If a peer group is not configured with a remote-as option, the members can be configured with the neighbor {ip-address | peer-group-name} remote-ascommand. This command allows you to create peer groups containing external BGP (eBGP) neighbors.

Examples

The following example configurations show how to create these types of neighbor peer group:

•internal Border Gateway Protocol (iBGP) peer group

•eBGP peer group

•Multiprotocol BGP peer group

iBGP Peer Group

In the following example, the peer group named internal configures the members of the peer group to be iBGP neighbors. By definition, this is an iBGP peer group because the router bgp command and the neighbor remote-as command indicate the same autonomous system (in this case, autonomous system 100). All the peer group members use loopback 0 as the update source and use set-med as the outbound route map. The neighbor internalfilter-list 2 in command shows that, except for 172.16.232.55, all the neighbors have filter list 2 as the inbound filter list.

router bgp 100

 neighbor internal peer-group

 neighbor internal remote-as 100

 neighbor internal update-source loopback 0

 neighbor internal route-map set-med out

 neighbor internal filter-list 1 out

 neighbor internal filter-list 2 in

 neighbor 172.16.232.53 peer-group internal

 neighbor 172.16.232.54 peer-group internal

 neighbor 172.16.232.55 peer-group internal

 neighbor 172.16.232.55 filter-list 3 in

eBGP Peer Group

The following example defines the peer group named external-peers without the neighbor remote-as command. By definition, this is an eBGP peer group because each individual member of the peer group is configured with its respective autonomous system number separately. Thus the peer group consists of members from autonomous systems 200, 300, and 400. All the peer group members have the set-metric route map as an outbound route map and filter list 99 as an outbound filter list. Except for neighbor 172.16.232.110, all of them have 101 as the inbound filter list.

router bgp 100

 neighbor external-peers peer-group

 neighbor external-peers route-map set-metric out

 neighbor external-peers filter-list 99 out

 neighbor external-peers filter-list 101 in

 neighbor 172.16.232.90 remote-as 200

 neighbor 172.16.232.90 peer-group external-peers

 neighbor 172.16.232.100 remote-as 300

 neighbor 172.16.232.100 peer-group external-peers

 neighbor 172.16.232.110 remote-as 400

 neighbor 172.16.232.110 peer-group external-peers

 neighbor 172.16.232.110 filter-list 400 in

Multiprotocol BGP Peer Group

In the following example, all members of the peer group are multicast-capable:

router bgp 100

neighbor 10.1.1.1 remote-as 1

neighbor 172.16.2.2 remote-as 2

address-family ipv4 multicast

 neighbor mygroup peer-group

 neighbor 10.1.1.1 peer-group mygroup

 neighbor 172.16.2.2 peer-group mygroup

 neighbor 10.1.1.1 activate

 neighbor 172.16.2.2 activate

Related Commands

Command	Description
address-family ipv4 (BGP)	Places the router in address family configuration mode for configuring routing sessions such as BGP, RIP, or static routing sessions that use standard IPv4 address prefixes.
address-family vpnv4	Places the router in address family configuration mode for configuring routing sessions such as BGP, RIP, or static routing sessions that use standard VPNv4 address prefixes.
clear ip bgp peer-group	Removes all the members of a BGP peer group.
show ip bgp peer-group	Displays information about BGP peer groups.

Files:
Topology
Configs
BGP Configuration