Cisco IOS XE IP Routing Protocols Configuration Guide, Release 2
BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN
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Table Of Contents

BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

Finding Feature Information

Contents

Prerequisites for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

Restrictions for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

Information About BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

Multipath Load Sharing Between eBGP and iBGP

eBGP and iBGP Multipath Load Sharing in a BGP MPLS Network

eBGP and iBGP Multipath Load Sharing with Route Reflectors

Benefits of Multipath Load Sharing for Both eBGP and iBGP

How to Configure BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

Configuring Multipath Load Sharing for Both eBGP an iBGP

Verifying Multipath Load Sharing for Both eBGP an iBGP

Configuration Examples for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

eBGP and iBGP Multipath Load Sharing Configuration: Example

eBGP and iBGP Multipath Load Sharing Verification: Examples

Where to Go Next

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN


BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

First Published: 2004
Last Updated: May 4, 2009

The BGP Multipath Load Sharing for both eBGP and iBGP in an MPLS-VPN feature allows you to configure multipath load balancing with both external BGP (eBGP) and internal BGP (iBGP) paths in Border Gateway Protocol (BGP) networks that are configured to use Multiprotocol Label Switching (MPLS) Virtual Private Networks (VPNs). This feature provides improved load balancing deployment and service offering capabilities and is useful for multihomed autonomous systems and Provider Edge (PE) routers that import both eBGP and iBGP paths from multihomed and stub networks.

Finding Feature Information

For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Prerequisites for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

•Restrictions for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

•Information About BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

•How to Configure BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

•Configuration Examples for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

•Where to Go Next

•Additional References

•Feature Information for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

Prerequisites for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

Load Balancing is Configured Under Cisco Express Forwarding

Cisco Express Forwarding or distributed Cisco Express Forwarding must be enabled on all participating routers.

Restrictions for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

Address Family Support

This feature is configured on a per VPN routing and forwarding instance (VRF) basis. This feature can be configured under only the IPv4 VRF address family.

Memory Consumption Restriction

Each BGP multipath routing table entry will use additional memory. We recommend that you do not use this feature on a router with a low amount of available memory and especially if router is carries full Internet routing tables.

Route Reflector Limitation

When multiple iBGP paths installed in a routing table, a route reflector will advertise only one paths (next hop). If a router is behind a route reflector, all routers that are connected to multihomed sites will not be advertised unless a different route distinguisher is configured for each VRF.

Information About BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

To configure the BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN feature, you should understand the following concepts:

•Multipath Load Sharing Between eBGP and iBGP

•eBGP and iBGP Multipath Load Sharing in a BGP MPLS Network

•eBGP and iBGP Multipath Load Sharing with Route Reflectors

•Benefits of Multipath Load Sharing for Both eBGP and iBGP

Multipath Load Sharing Between eBGP and iBGP

A BGP routing process will install a single path as the best path in the routing information base (RIB) by default. The maximum-paths command allows you to configure BGP to install multiple paths in the RIB for multipath load sharing. BGP uses the best path algorithm to still select a single multipath as the best path and advertise the best path to BGP peers.

Note The number of paths of multipaths that can be configured is documented on the maximum-paths command reference page.

Load balancing over the multipaths is performed by Cisco Express Forwarding. Cisco Express Forwarding load balancing is configured on a per-packet round robin or on a per session (source and destination pair) basis.

The BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN feature is enabled only under the IPv4 VRF address family configuration mode. When enabled, this feature can perform load balancing on eBGP and/or iBGP paths that are imported into the VRF. The number of multipaths is configured on a per VRF basis. Separate VRF multipath configurations are isolated by unique route distinguisher.

Note The BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN feature operates within the parameters of configured outbound routing policy.

eBGP and iBGP Multipath Load Sharing in a BGP MPLS Network

Figure 1 shows a service provider BGP MPLS network that connects two remote networks to PE router 1 and PE router 2. PE router 1 and PE router 2 are both configured for VPNv4 unicast iBGP peering. Network 2 is a multihomed network that is connected to PE router 1 and PE router 2. Network 2 also has extranet VPN services configured with Network 1. Both Network 1 and Network 2 are configured for eBGP peering with the PE routers.

Figure 1

A Service Provider BGP MPLS Network

PE router 1 can be configured with the BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN feature so that both iBGP and eBGP paths can be selected as multipaths and imported into the VRF of Network 1. The multipaths will be used by Cisco Express Forwarding to perform load balancing. IP traffic that is sent from Network 2 to PE router 1 and PE router 2 will be sent across the eBGP paths as IP traffic. IP traffic that is sent across the iBGP path will be sent as MPLS traffic, and MPLS traffic that is sent across an eBGP path will be sent as IP traffic. Any prefix that is advertised from Network 2 will be received by PE router 1 through route distinguisher (RD) 21 and RD 22.The advertisement through RD 21 will be carried in IP packets, and the advertisement through RD 22 will be carried in MPLS packets. Both paths can be selected as multipaths for VRF1 and installed into the VRF1 RIB.

eBGP and iBGP Multipath Load Sharing with Route Reflectors

Figure 2 shows a topology that contains three PE routers and a route reflector, all configured for iBGP peering. PE router 2 and PE router 3 each advertise an equal preference eBGP path to PE router 1. By default, the route reflector will choose only one path and advertise PE router 1.

Figure 2

A Topology with a Route Reflector

For all equal preference paths to PE router 1 to be advertised through the route reflector, you must configure each VRF with a different RD. The prefixes received by the route reflector will be recognized differently and advertised to PE router 1.

Benefits of Multipath Load Sharing for Both eBGP and iBGP

The BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN feature allows multihomed autonomous systems and PE routers to be configured to distribute traffic across both eBGP and iBGP paths.

How to Configure BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

This section contains the following procedures:

•Configuring Multipath Load Sharing for Both eBGP an iBGP

•Verifying Multipath Load Sharing for Both eBGP an iBGP

Configuring Multipath Load Sharing for Both eBGP an iBGP

To configure this feature, perform the steps in this section.

SUMMARY STEPS

1. enable

2. configure terminal

3. router bgp autonomous-system-number

4. address-family ipv4 [mdt | multicast | tunnel | unicast [vrf vrf-name] | vrf vrf-name] | ipv6 [multicast | unicast] | vpnv4 [unicast]

5. maximum-paths eibgp number [import number]

6. end

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

router bgp autonomous-system-number

Example:

Router(config)# router bgp 40000

Enters router configuration mode to create or configure a BGP routing process.

Step 4 

address-family ipv4 vrf vrf-name

Example:

Router(config-router)# address-family ipv4 vrf RED

Places the router in address family configuration mode.

•Separate VRF multipath configurations are isolated by unique route distinguisher.

Step 5 

maximum-paths eibgp number [import number]

Example:

Router(config-router-af)# maximum-paths eibgp 6

Configures the number of parallel iBGP and eBGP routes that can be installed into a routing table.

Note The maximum-paths eibgp command can be configured only under the IPv4 VRF address family configuration mode and cannot be configured in any other address family configuration mode.

Step 6 

end

Example:

Router(config-router-af)# end

Exits address family configuration mode and returns to privileged EXEC mode.

Verifying Multipath Load Sharing for Both eBGP an iBGP

To verify this feature, perform the steps in this section.SUMMARY STEPS

1. enable

2. show ip bgp neighbors [neighbor-address [advertised-routes | dampened-routes | flap-statistics | paths [regexp] | received prefix-filter | received-routes | routes]]

3. show ip bgp vpnv4 {all | rd route-distinguisher | vrf vrf-name}

4. show ip route vrf vrf-name

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

show ip bgp neighbors [neighbor-address [advertised-routes | dampened-routes | flap-statistics | paths [regexp] | received prefix-filter | received-routes | routes]]

Example:

Router# show ip bgp neighbors

Displays information about the TCP and BGP connections to neighbors.

Step 3 

show ip bgp vpnv4 {all | rd route-distinguisher | vrf vrf-name}

Example:

Router# show ip bgp vpnv4 vrf RED

Displays VPN address information from the BGP table. This command is used to verify that the VRF has been received by BGP.

Step 4 

show ip route vrf vrf-name

Example:

Router# show ip route vrf RED

Displays the IP routing table associated with a VRF instance. The show ip route vrf command is used to verify that the VRF is in the routing table.

Configuration Examples for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

The following examples show how to configure and verify this feature:

•eBGP and iBGP Multipath Load Sharing Configuration: Example

•eBGP and iBGP Multipath Load Sharing Verification: Examples

eBGP and iBGP Multipath Load Sharing Configuration: Example

This following configuration example configures a router in address-family mode to select six BGP routes (eBGP or iBGP) as multipaths: 

Router(config)# router bgp 40000 

Router(config-router)# address-family ipv4 vrf RED 

Router(config-router-af)# maximum-paths eibgp 6 

Router(config-router-af)# end

eBGP and iBGP Multipath Load Sharing Verification: Examples

To verify that iBGP and eBGP routes have been configured for load sharing, use the show ip bgp vpnv4 command or the show ip route vrf command.

In the following example, the show ip bgp vpnv4 command is entered to display multipaths installed in the VPNv4 RIB: 

Router# show ip bgp vpnv4 all 10.22.22.0


BGP routing table entry for 10:1:22.22.22.0/24, version 19

Paths:(5 available, best #5)

Multipath:eiBGP

  Advertised to non peer-group peers:

  10.0.0.2 10.0.0.3 10.0.0.4 10.0.0.5

  22

    10.0.0.2 (metric 20) from 10.0.0.4 (10.0.0.4)

      Origin IGP, metric 0, localpref 100, valid, internal, multipath

      Extended Community:0x0:0:0 RT:100:1 0x0:0:0

      Originator:10.0.0.2, Cluster list:10.0.0.4

  22

    10.0.0.2 (metric 20) from 10.0.0.5 (10.0.0.5)

      Origin IGP, metric 0, localpref 100, valid, internal, multipath

      Extended Community:0x0:0:0 RT:100:1 0x0:0:0

      Originator:10.0.0.2, Cluster list:10.0.0.5

  22

    10.0.0.2 (metric 20) from 10.0.0.2 (10.0.0.2)

      Origin IGP, metric 0, localpref 100, valid, internal, multipath

      Extended Community:RT:100:1 0x0:0:0

  22

    10.0.0.2 (metric 20) from 10.0.0.3 (10.0.0.3)

      Origin IGP, metric 0, localpref 100, valid, internal, multipath

      Extended Community:0x0:0:0 RT:100:1 0x0:0:0

      Originator:10.0.0.2, Cluster list:10.0.0.3

  22

    10.1.1.12 from 10.1.1.12 (10.22.22.12)

      Origin IGP, metric 0, localpref 100, valid, external, multipath, best

      Extended Community:RT:100:1

In the following example, the show ip route vrf command is entered to display multipath routes in the VRF table: 

Router# show ip route vrf PATH 10.22.22.0


Routing entry for 10.22.22.0/24

  Known via "bgp 1", distance 20, metric 0

  Tag 22, type external

  Last update from 10.1.1.12 01:59:31 ago

  Routing Descriptor Blocks:

  * 10.0.0.2 (Default-IP-Routing-Table), from 10.0.0.4, 01:59:31 ago

      Route metric is 0, traffic share count is 1

      AS Hops 1

    10.0.0.2 (Default-IP-Routing-Table), from 10.0.0.5, 01:59:31 ago

      Route metric is 0, traffic share count is 1

      AS Hops 1

    10.0.0.2 (Default-IP-Routing-Table), from 10.0.0.2, 01:59:31 ago

      Route metric is 0, traffic share count is 1

      AS Hops 1

    10.0.0.2 (Default-IP-Routing-Table), from 10.0.0.3, 01:59:31 ago

      Route metric is 0, traffic share count is 1

      AS Hops 1

    10.1.1.12, from 10.1.1.12, 01:59:31 ago

      Route metric is 0, traffic share count is 1

      AS Hops 1

Where to Go Next

For information about advertising the bandwidth of an autonomous system exit link as an extended community, refer to the "BGP Link Bandwidth" document.

Additional References

For additional information related to the BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN feature, see to the following references.

Related Documents

Related Topic
Document Title

BGP commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples

Cisco IOS IP Routing Protocols Command Reference

Comprehensive BGP link bandwidth configuration examples and tasks

BGP Link Bandwidth

Cisco IOS master command list, all  releases

Cisco IOS Master Command List, All Releases


Standards

Standards
Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

—


MIBs

MIBs
MIBs Link

No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

To locate and download MIBs for selected platforms, Cisco IOS XE software releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs


RFCs

RFCs
Title

RFC 1771

A Border Gateway Protocol 4 (BGP4)

RFC 2547

BGP/MPLS VPNs

RFC 2858

Multiprotocol Extensions for BGP-4


Technical Assistance

Description
Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/techsupport


Feature Information for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

Table 1 lists the release history for this feature.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 1 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.

Table 1 Feature Information for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN 

Feature Name
Releases
Feature Information

BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN

Cisco IOS XE Release 2.1

This feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.


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