Table Of Contents
Loadsharing IP Packets over More Than Six Parallel Paths
Restrictions for Loadsharing IP Packets over More Than Six Parallel Paths
Loadsharing IP Packets over More Than Six Parallel Paths Overview
Loadsharing IP Packets over More Than Six Parallel Paths
The Loadsharing IP Packets over More Than Six Parallel Paths feature increases the maximum number of parallel routes that can be installed to the routing table for multipath loadsharing.
Feature History for the Loadsharing IP Packets over More Than Six Parallel Paths Feature
Finding Support Information for Platforms and Cisco IOS Software Images
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Contents
•Restrictions for Loadsharing IP Packets over More Than Six Parallel Paths
•Loadsharing IP Packets over More Than Six Parallel Paths Overview
Restrictions for Loadsharing IP Packets over More Than Six Parallel Paths
The Loadsharing IP Packets Over More Than Six Parallel Paths feature is only available in software images for supported platforms in Cisco IOS Release 12.3(2)T and later 12.3T releases.
Loadsharing IP Packets over More Than Six Parallel Paths Overview
The Loadsharing IP Packets over More Than Six Parallel Paths feature increases the maximum number of parallel routes that can be installed to the routing table. The maximum number has been increased from six to sixteen for the following commands:
•maximum-paths
•maximum-paths eibgp
•maximum-paths ibgp
The output of the show ip route summary command has been updated to show the number of parallel routes supported by the routing table.
The benefits of this feature include the following:
•More flexible configuration of parallel routes in the routing table.
•Ability to configure multipath loadsharing over more links to allow for the configuration of higher-bandwidth aggregation using lower-speed links.
Additional References
For additional information related to multipath load sharing and the configuration of parallel routes, refer to the following references:
Related Documents
Related Topic Document TitleMultipath Load Sharing and Routing
Cisco IOS IP Configuration Guide, Release 12.3
Cisco IOS IP Command Reference, Volume 2 of 4: Routing Protocols, Release 12.3
eiBGP Multipath Load Sharing
BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN
iBGP Multipath Load Sharing
MIBs
RFCs
RFCs 1 TitleNo new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.
—
1 Not all supported RFCs are listed.
Technical Assistance
Description LinkTechnical 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.
TAC Home Page:
http://www.cisco.com/public/support/tac/home.shtml
BGP Support Page:
http://www.cisco.com/cgi-bin/Support/browse/psp_view.pl?p=Internetworking:BGP
Command Reference
This section documents modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.3 command reference publications.
maximum-paths
To control the maximum number of parallel routes an IP routing protocol can support, use the maximum-paths command in router configuration mode. To restore the default value, use the no form of this command.
maximum-paths {[number-of-paths] [import number-of-paths] | [import number-of-paths]}
no maximum-paths
Syntax Description
Defaults
Border Gateway Protocol (BGP) by default will install only one best path into the routing table. The default for all other IP routing protocols is four paths.
Command Modes
Router configuration
Address-family configuration
Command History
Usage Guidelines
The maximum-paths command is used to install parallel routes into the BGP routing table. The maximum-paths command cannot be configured with the maximum-paths eibgp command.
Configuring VRF Multipaths
A VRF will import only one path (the best path) per prefix from the source VRF table, unless the prefix is exported with a different route-target. If the best path goes down, the destination will not be reachable until the next import event occurs, and then a new best path will be imported into the VRF table. The import event runs every 15 seconds by default.
The import keyword allows the network operator to configure the VRF table to accept multiple redundant paths in addition to the best path. This feature should be used when there are multiple paths with identical next hops available to ensure optimal convergence times. A typical application of this configuration option is to configure redundant paths in a network that has multiple route reflectors for redundancy.
Note Configuring redundant paths with the import keyword can increase CPU and memory utilization significantly, especially in a network where there are many prefixes to learn and a large number of configured VRFs. It is recommended that this feature is only configured as necessary and that the minimum number of redundant paths are configured (Typically, not more than two).
Examples
The following example configuration installs 2 parallel routes in the BGP routing table:
Router(config)# router bgp 100Router(config-router)# maximum-paths 2Router(config-router)# endThe following example configuration installs 6 parallel routes in the BGP routing table and 2 parallel routes in the VRF table:
Router(config)# router bgp 100Router(config-router)# address-family ipv4 vrf vrf-nameRouter(config-router-af)# maximum-paths 6 import 2Router(config-router-af)# endThe following example configuration installs 2 parallel routes in the VRF table:
Router(config)# router bgp 100Router(config-router)# address-family ipv4 vrf vrf-nameRouter(config-router-af)# maximum-paths import 2Router(config-router-af)# endmaximum-paths eibgp
To configure multipath load sharing for external BGP (eBGP) and internal (iBGP) routes, use the maximum-paths eibgp command in address family configuration mode. To disable multipath load sharing for eBGP and iBGP routes, use the no form of this command.
maximum-paths eibgp number [import number]
no maximum-paths eibgp number [import number]
Syntax Description
Defaults
Border Gateway Protocol (BGP) by default will install only one best path in the routing table.
Command Modes
IPv4 VRF Address family configuration
Command History
Usage Guidelines
The maximum-paths eibgp command used to configure Border Gateway Protocol (BGP) multipath load sharing in an Multiprotocol Label Switching (MPLS) virtual private network (VPN) using eBGP and iBGP routes. This feature is configured under a VPN routing and forwarding instance (VRF) in address family configuration mode. The number of multipaths is configured separately for each VRF. The number of paths that can be configured is determined by the version of Cisco IOS software. The following list shows current limits:
•Cisco IOS Release 12.0S based software: 8 paths
•Cisco IOS Release 12.3T based software: 16 paths
•Cisco IOS Release 12.2S based software: 32 paths
The maximum-paths eibgp command cannot be configured with the maximum-paths or maximum-paths ibgp command because the maximum-paths eibgp command is a superset of these commands.
Note The configuration of this command does not override the existing outbound routing policy.
Configuring VRF Import Paths
A VRF will import only one path (best path) per prefix from the source VRF table, unless the prefix is exported with a different route-target. If the best path goes down, the destination will not be reachable until the next import event occurs, and then a new best path will be imported into the VRF table. The import event runs every 15 seconds by default.
The import keyword allows you to configure the VRF table to accept multiple redundant paths in addition to the best path. An import path is a redundant path, and it can have a next hop that matches an installed multipath.This feature should be used when there are multiple paths with identical next hops available to ensure optimal convergence times. A typical application of this feature is to configure redundant paths in a network that has multiple route reflectors for redundancy.
Note Configuring redundant paths with the import keyword can increase CPU and memory utilization significantly, especially in a network where there are many prefixes to learn and a large number of configured VRFs. It is recommended that this feature is only configured as necessary and that the minimum number of redundant paths are configured (Typically, not more than two).
Examples
In the following example, the router is configured to install 6 eBGP or iBGP routes into the VRF routing table:
Router(config)# router bgp 40000
Router(config-router)# address-family ipv4 vrf YELLOW
Router(config-router-af)# maximum-paths eibgp 6
In the following example, the router is configured to install 4 equal-cost routes and 2 import routes (backup) in the VRF routing table:
Router(config)# router bgp 45000
Router(config-router)# address-family ipv4 vrf GREEN
Router(config-router-af)# maximum-paths eibgp 4 import 2
In the following example, the router is configured to install 2 import routes in the VRF routing table:
Router(config)# router bgp 50000
Router(config-router)# address-family ipv4 vrf ORANGE
Router(config-router-af)# maximum-paths eibgp import 2
Note Separate VRFs must be configured with different route distinguisher to support separate multipath configurations.
Related Commands
maximum-paths ibgp
To control the maximum number of parallel internal Border Gateway Protocol (iBGP) routes that can be installed in a routing table, use the maximum-paths ibgp command in router configuration mode. To restore the default value, use the no form of this command.
maximum-paths ibgp {[number] [import number] | [import number]}
no maximum-paths ibgp
Syntax Description
Defaults
BGP, by default, will install only one best path in the routing table.
Command Modes
Address-family configuration
Router configurationCommand History
Usage Guidelines
iBGP Multipath Load Sharing
The iBGP Multipath Load Sharing feature is enabled when the following conditions are met:
•The maximum-paths ibgp command must be set to a value greater than one.
•All attributes must be the same. The attributes include weight, local preference, autonomous system path (entire attribute and not just length), origin code, Multi Exit Discriminator (MED), and Interior Gateway Protocol (IGP) distance.
•The next hop router for each multipath must be different.
Even if the criteria are met and multiple paths are considered multipaths, a BGP-speaking router will still designate one of the multipaths as the best path and advertise this best path to its neighbors.
The number of paths that can be configured is determined by the version of Cisco IOS software. The following list shows current limits:
•Cisco IOS Release 12.0S-based software: 8 paths
•Cisco IOS Release 12.3T-based software: 16 paths
•Cisco IOS Release 12.2S-based software: 32 paths
Note In IPv6, the maximum-paths ibgp command does not work for prefixes learned from iBGP neighbors that have been configured with the send-label keyword. If multiple routes exist for such prefixes, all of them are inserted into the RIB when the maximum-paths ibgp command is configured, but only one is used and no load balancing occurs between equal-cost paths.
The maximum-paths ibgp command works with 6PE only in Cisco IOS Release 12.2(25)S and subsequent 12.2S releases.
Configuring VRF Multipaths
A VRF will import only one path (the best path) per prefix from the source VRF table, unless the prefix is exported with a different route-target. If the best path goes down, the destination will not be reachable until the next import event occurs, and then a new best path will be imported into the VRF table. The import event runs every 15 seconds by default.
The import keyword allows the network operator to configure the VRF table to accept multiple redundant paths in addition to the best path. This feature should be used when there are multiple paths with identical next hops available to ensure optimal convergence times. A typical application of this configuration option is to configure redundant paths in a network that has multiple route reflectors for redundancy.
Note Configuring redundant paths with the import keyword can increase CPU and memory utilization significantly, especially in a network where there are many prefixes to learn and a large number of configured VRFs. It is recommended that this feature is only configured as necessary and that the minimum number of redundant paths are configured (Typically, not more than two).
Examples
The following example configuration installs 3 parallel iBGP paths in a non-Multiprotocol Label Switching (MPLS) topology:
Router(config)# router bgp 100
Router(config-router)# maximum-paths ibgp 3
The following example configuration installs 3 parallel iBGP paths in an MPLS Virtual Private Network (VPN) topology:
Router(config)# router bgp 100
Router(config-router)# address-family ipv4 unicast vrf RED
Router(config-route-af)# maximum-paths ibgp 3
The following example configuration installs 2 parallel routes in the VRF table:
Router(config)# router bgp 100
Router(config-router)# address-family ipv4 vrf BLUE
Router(config-router-af)# maximum-paths ibgp 2 import 2
Router(config-router-af)# end
The following example configuration installs 2 parallel routes in the VRF table:
Router(config)# router bgp 100
Router(config-router)# address-family ipv4 vrf GREEN
Router(config-router-af)# maximum-paths ibgp import 2
Router(config-router-af)# end
Related Commands
Command Descriptionmaximum-paths
Controls the maximum number of parallel routes an IP routing protocol can support.
show ip route summary
To display the current state of the routing table, use the show ip route summary command in EXEC mode.
show ip route summary
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Examples
The following is sample output from the show ip route summary command:
Router# show ip route summaryIP routing table name is Default-IP-Routing-Table(0)IP routing table maximum-paths is 16Route Source Networks Subnets Overhead Memory (bytes)connected 0 3 126 360static 1 2 126 360eigrp 109 747 12 31878 91080internal 3 360Total 751 17 32130 92160Table 1 describes the significant fields shown in the display.
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