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The BGP Multipath Load Sharing for eBGP and iBGP 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 multi-homed autonomous systems and Provider Edge (PE) routers that import both eBGP and iBGP paths from multihomed and stub networks.
Cisco Express Forwarding (CEF) or distributed CEF (dCEF) must be enabled on all participating devices.
This feature is configured on a per VPN routing and forwarding instance (VRF) basis. This feature can be configured under both IPv4 and IPv6 VRF address families.
Each BGP multipath routing table entry will use additional memory. We recommend that you do not use this feature on a device with a low amount of available memory and especially if the device carries full Internet routing tables.
The number of paths supported are limited to 2 BGP multipaths. This could either be 2 iBGP multipaths or 1 iBGP multipath and 1 eBGP multipath.
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 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 CEF. CEF load balancing is configured on a per-packet round robin or on a per session (source and destination pair) basis. For information about CEF, refer to Cisco IOS IP Switching Configuration Guide documentation:http://ciscosystems.com/en/US/docs/ios/ipswitch/configuration/guide/12_2sx/isw_12_2sx_book.html.The BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN feature is enabled under the IPv4 VRF address family and IPv6 VRF address family configuration modes. 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. |
The following figure 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.
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 . The multipaths will be used by CEF to perform load balancing. IP traffic that is sent from Network 1 to Network 2, PE router 1 will Load Sharing with eBGP paths as IP traffic & iBGP path will be sent as MPLS traffic.
Note |
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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.
This section contains the following procedures:
Command or Action | Purpose | |
---|---|---|
Step 1 | enable
Example: Device> enable
|
Enables privileged EXEC mode. |
Step 2 | show ip bgp neighbors
Example: Device# show ip bgp neighbors
|
Displays information about the TCP and BGP connections to neighbors. |
Step 3 | show ip bgp vpnv4 vrfvrf name
Example: Device# 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 vrfvrf-name Example: Device# 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. |
The following examples show how to configure and verify this feature:
This following configuration example configures a router in IPv4 address-family mode to select two BGP routes (eBGP or iBGP) as multipaths:
Device router bgp 40000 Deviceaddress-family ipv4 vrf RED Devicemaximum-paths eibgp 2 Deviceend
This following configuration example configures a router in IPv6 address-family mode to select two BGP routes (eBGP or iBGP) as multipaths:
Device router bgp 40000 Deviceaddress-family ipv6 vrf RED Devicemaximum-paths eibgp 2 Deviceend
Related Topic |
Document Title |
---|---|
BGP commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples |
• Cisco IOS IP Command Reference, Volume 2 of 4: Routing Protocols, Release 12.3T |
BGP configuration tasks |
• Cisco IOS IP Configuration Guide, Release 12.3 |
Comprehensive BGP link bandwidth configuration examples and tasks |
• BGP Link Bandwidth |
CEF configuration tasks |
• Cisco IOS Switching Services Configuration Guide |
Standard |
Title |
---|---|
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature |
-- |
RFC |
Title |
---|---|
RFC 1771 |
A Border Gateway Protocol 4 (BGP4) |
RFC 2547 |
BGP/MPLS VPNs |
RFC 2858 |
Multiprotocol Extensions for BGP-4 |
Description |
Link |
---|---|
Technical Assistance Center (TAC) home page, containing 30,000 pages of searchable technical content, including links to products, technologies, solutions, technical tips, tools, and lots more. Registered Cisco.com users can log in from this page to access even more content. |
http://www.cisco.com/public/support/tac/home.shtml |
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Feature Name |
Releases |
Feature Information |
---|---|---|
BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN |
Cisco IOS 16.6.1 |
The BGP Multipath Load Sharing for eBGP and iBGP 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 multi-homed autonomous systems and Provider Edge (PE) routers that import both eBGP and iBGP paths from multihomed and stub networks. |