Cisco Configuring eBGP and iBGP Multipath: Comprehensive Guide & User Manual PDF (EN)

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

Configuring eBGP and iBGP Multipath BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN, on page 1 Information About BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN, on page 2 How to Configure BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN, on page 4 Configuration Examples for the BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN, on page 5 Feature History for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN, on page 6 BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN 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. Prerequisites for BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN Cisco Express Forwarding (CEF) or distributed CEF (dCEF) must be enabled on all participating devices. 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 both IPv4 and IPv6 VRF address families.

Configuring eBGP and iBGP Multipath 1

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Multipath Load Sharing Between eBGP and iBGP

The maximum-paths feature is not supported on the IPv4 and IPv6 address families with MPLS deployments. Memory Consumption Restriction 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. Number of Paths Limitation 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. Unsupported Commands ip unnumbered command is not supported in MPLS configuration.

Information About BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN 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 select a single multipath as the best path and advertise the best path to BGP peers. The valid values for the maximum-paths command range from 1 to 32. However, the maximum value that can be configured is 2. Note 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, see IP Switching Cisco Express Forwarding Configuration Guide . 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.

The BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN feature operates within the parameters of configured outbound routing policy. Note Configuring eBGP and iBGP Multipath Information About BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN Configuring eBGP and iBGP Multipath 2

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Benefits of Multipath Load Sharing for Both eBGP and iBGP

eBGP and iBGP Multipath Load Sharing in a BGP MPLS Network 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. Figure 1:

Service Provider BGP MPLS Network Connected to 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 Share with eBGP paths as IP traffic & iBGP path will be sent as MPLS traffic. Note • eBGP session between local CE & local PE is not supported. • eBGP session from a local PE to a remote CE is supported. • eiBGP Multipath is supported in per prefix label allocation mode only.

It is not supported in other label allocation modes. 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. Configuring eBGP and iBGP Multipath eBGP and iBGP Multipath Load Sharing in a BGP MPLS Network Configuring eBGP and iBGP Multipath 3

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Configuring Multipath Load Sharing for Both eBGP an iBGP in an MPLS VPN

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 in an MPLS VPN Procedure Configuring eBGP and iBGP Multipath How to Configure BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN Command or Action Purpose Step 1 enable Example: Device> enable Enables privileged EXEC mode. • Enter your password if prompted. Step 2 configure{terminal|memory|network} Example: Device# configure terminal Enters global configuration mode. Step 3 router bgp as-number Example:

Device(config)# router bgp 40000 Enters router configuration mode to create or configure a BGP routing process. Step 4 neighbor {ip-address | ipv6-address | peer-group-name } Example: Device(config-router)# neighbor group192 Accepts and attempts BGP connections to external peers residing on networks that are not directly connected. Step 5 address-family ipv4 vrfvrf-name Example: Device(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 6 address-family ipv6 vrfvrf-name Example:

Device(config-router)# address-family ipv6 vrf RED Places the router in address family configuration mode. • Separate VRF multipath configurations are isolated by unique route distinguisher. Step 7 neighbor {ip-address | ipv6-address | peer-group-name } update-source interface-type interface-name Example: Specifies the link-local address over which the peering is to occur. Configuring eBGP and iBGP Multipath 4

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