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Table Of Contents
Prerequisites for BGP Link Bandwidth
Restrictions for BGP Link Bandwidth
Information About BGP Link Bandwidth
Link Bandwidth Extended Community Attribute
Benefits of the BGP Link Bandwidth Feature
How to Configure BGP Link Bandwidth
Configuring and Verifying BGP Link Bandwidth
Configuration Examples for BGP Link Bandwidth
Example: BGP Link Bandwidth Configuration
Feature Information for BGP Link Bandwidth
BGP Link Bandwidth
The BGP (Border Gateway Protocol) Link Bandwidth feature is used to advertise the bandwidth of an autonomous system exit link as an extended community. This feature is configured for links between directly connected external BGP (eBGP) neighbors. The link bandwidth extended community attribute is propagated to iBGP peers when extended community exchange is enabled. This feature is used with BGP multipath features to configure load balancing over links with unequal bandwidth.
Finding Feature Information
Your software release may not support all the features documented in this module. 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 Link Bandwidth" section.
Use Cisco Feature Navigator to find information about platform support and Cisco 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
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Prerequisites for BGP Link Bandwidth
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Prerequisites for BGP Link Bandwidth
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Restrictions for BGP Link Bandwidth
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Information About BGP Link Bandwidth
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BGP Link Bandwidth Overview
The BGP Link Bandwidth feature is used to enable multipath load balancing for external links with unequal bandwidth capacity. This feature is enabled under an IPv4 or VPNv4 address family session by entering the bgp dmzlink-bw command. This feature supports iBGP, eBGP multipath load balancing, and eiBGP multipath load balancing in Multiprotocol Label Switching (MPLS) VPNs. When this feature is enabled, routes learned from directly connected external neighbor are propagated through the internal BGP (iBGP) network with the bandwidth of the source external link.
The link bandwidth extended community indicates the preference of an autonomous system exit link in terms of bandwidth. This extended community is applied to external links between directly connected eBGP peers by entering the neighbor dmzlink-bw command. The link bandwidth extended community attribute is propagated to iBGP peers when extended community exchange is enabled with the neighbor send-community command.
Link Bandwidth Extended Community Attribute
The link bandwidth extended community attribute is a 4-byte value that is configured for a link on the demilitarized zone (DMZ) interface that connects two single hop eBGP peers. The link bandwidth extended community attribute is used as a traffic sharing value relative to other paths while traffic is being forwarded. Two paths are designated as equal for load balancing if the weight, local-pref, as-path length, Multi Exit Discriminator (MED), and Interior Gateway Protocol (IGP) costs are the same.
Benefits of the BGP Link Bandwidth Feature
The BGP Link Bandwidth feature allows BGP to be configured to send traffic over multiple iBGP or eBGP learned paths where the traffic that is sent is proportional to the bandwidth of the links that are used to exit the autonomous system. The configuration of this feature can be used with eBGP and iBGP multipath features to enable unequal cost load balancing over multiple links. Unequal cost load balancing over links with unequal bandwidth was not possible in BGP before the BGP Link Bandwidth feature was introduced.
How to Configure BGP Link Bandwidth
Configuring and Verifying BGP Link Bandwidth (required)
Configuring and Verifying BGP Link Bandwidth
To configure the BGP Link Bandwidth feature, perform the steps in this section.
SUMMARY STEPS
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DETAILED STEPS
Configuration Examples for BGP Link Bandwidth
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Example: BGP Link Bandwidth Configuration
In the following examples, the BGP Link Bandwidth feature is configured so BGP will distribute traffic proportionally to the bandwidth of each external link. Figure 1 shows two external autonomous systems connected by three links that each carry a different amount of bandwidth (unequal cost links). Multipath load balancing is enabled and traffic is balanced proportionally.
Note
Caution
Figure 1
BGP Link Bandwidth Configuration
Router A Configuration
In the following example, Router A is configured to support iBGP multipath load balancing and to exchange the BGP extended community attribute with iBGP neighbors:
RouterA(config)# router bgp 100RouterA(config-router)# neighbor 10.10.10.2 remote-as 100RouterA(config-router)# neighbor 10.10.10.2 update-source Loopback 0RouterA(config-router)# neighbor 10.10.10.3 remote-as 100RouterA(config-router)# neighbor 10.10.10.3 update-source Loopback 0RouterA(config-router)# address-family ipv4RouterA(config-router-af)# bgp dmzlink-bwRouterA(config-router-af)# neighbor 10.10.10.2 activateRouterA(config-router-af)# neighbor 10.10.10.2 send-community bothRouterA(config-router-af)# neighbor 10.10.10.3 activateRouterA(config-router-af)# neighbor 10.10.10.3 send-community bothRouterA(config-router-af)# maximum-paths ibgp 6Router B Configuration
In the following example Router B is configured to support multipath load balancing, to distribute Router D and Router E link traffic proportionally to the bandwidth of each link, and to advertise the bandwidth of these links to iBGP neighbors as an extended community:
RouterB(config)# router bgp 100RouterB(config-router)# neighbor 10.10.10.1 remote-as 100RouterB(config-router)# neighbor 10.10.10.1 update-source Loopback 0RouterB(config-router)# neighbor 10.10.10.3 remote-as 100RouterB(config-router)# neighbor 10.10.10.3 update-source Loopback 0RouterB(config-router)# neighbor 172.16.1.1 remote-as 200RouterB(config-router)# neighbor 172.16.1.1 ebgp-multihop 1RouterB(config-router)# neighbor 172.16.2.2 remote-as 200RouterB(config-router)# neighbor 172.16.2.2 ebgp-multihop 1RouterB(config-router)# address-family ipv4RouterB(config-router-af)# bgp dmzlink-bwRouterB(config-router-af)# neighbor 10.10.10.1 activateRouterB(config-router-af)# neighbor 10.10.10.1 next-hop-selfRouterB(config-router-af)# neighbor 10.10.10.1 send-community bothRouterB(config-router-af)# neighbor 10.10.10.3 activateRouterB(config-router-af)# neighbor 10.10.10.3 next-hop-selfRouterB(config-router-af)# neighbor 10.10.10.3 send-community bothRouterB(config-router-af)# neighbor 172.16.1.1 activateRouterB(config-router-af)# neighbor 172.16.1.1 dmzlink-bwRouterB(config-router-af)# neighbor 172.16.2.2 activateRouterB(config-router-af)# neighbor 172.16.2.2 dmzlink-bwRouterB(config-router-af)# maximum-paths ibgp 6RouterB(config-router-af)# maximum-paths 6Router C Configuration
In the following example Router C is configured to support multipath load balancing and to advertise the bandwidth of the link with Router E to iBGP neighbors as an extended community:
RouterC(config)# router bgp 100RouterC(config-router)# neighbor 10.10.10.1 remote-as 100RouterC(config-router)# neighbor 10.10.10.1 update-source Loopback 0RouterC(config-router)# neighbor 10.10.10.2 remote-as 100RouterC(config-router)# neighbor 10.10.10.2 update-source Loopback 0RouterC(config-router)# neighbor 172.16.3.30 remote-as 200RouterC(config-router)# neighbor 172.16.3.30 ebgp-multihop 1RouterC(config-router)# address-family ipv4RouterC(config-router-af)# bgp dmzlink-bwRouterC(config-router-af)# neighbor 10.10.10.1 activateRouterC(config-router-af)# neighbor 10.10.10.1 send-community bothRouterC(config-router-af)# neighbor 10.10.10.1 next-hop-selfRouterC(config-router-af)# neighbor 10.10.10.2 activateRouterC(config-router-af)# neighbor 10.10.10.2 send-community bothRouterC(config-router-af)# neighbor 10.10.10.2 next-hop-selfRouterC(config-router-af)# neighbor 172.16.3.3 activateRouterC(config-router-af)# neighbor 172.16.3.3 dmzlink-bwRouterC(config-router-af)# maximum-paths ibgp 6RouterC(config-router-af)# maximum-paths 6Verifying BGP Link Bandwidth
The examples in this section show the verification of this feature on Router A, Router B, and Router C.
Router B
In the following example, the show ip bgp command is entered on Router B to verify that two unequal cost best paths have been installed into the BGP routing table. The bandwidth for each link is displayed with each route.
RouterB# show ip bgp 192.168.1.0BGP routing table entry for 192.168.1.0/24, version 48Paths: (2 available, best #2)Multipath: eBGPAdvertised to update-groups:1 2200172.16.1.1 from 172.16.1.2 (192.168.1.1)Origin incomplete, metric 0, localpref 100, valid, external, multipath, bestExtended Community: 0x0:0:0DMZ-Link Bw 278 kbytes200172.16.2.2 from 172.16.2.2 (192.168.1.1)Origin incomplete, metric 0, localpref 100, valid, external, multipath, bestExtended Community: 0x0:0:0DMZ-Link Bw 625 kbytesRouter A
In the following example, the show ip bgp command is entered on Router A to verify that the link bandwidth extended community has been propagated through the iBGP network to Router A. Exit links are located on Router B and Router C. The output shows that a route for each exit link to autonomous system 200 has been installed as a best path in the BGP routing table.
RouterA# show ip bgp 192.168.1.0BGP routing table entry for 192.168.1.0/24, version 48Paths: (3 available, best #3)Multipath: eBGPAdvertised to update-groups:1 2200172.16.1.1 from 172.16.1.2 (192.168.1.1)Origin incomplete, metric 0, localpref 100, valid, external, multipathExtended Community: 0x0:0:0DMZ-Link Bw 278 kbytes200172.16.2.2 from 172.16.2.2 (192.168.1.1)Origin incomplete, metric 0, localpref 100, valid, external, multipath, bestExtended Community: 0x0:0:0DMZ-Link Bw 625 kbytes200172.16.3.3 from 172.16.3.3 (192.168.1.1)Origin incomplete, metric 0, localpref 100, valid, external, multipath, bestExtended Community: 0x0:0:0DMZ-Link Bw 2500 kbytesRouter A
In the following example, the show ip route command is entered on Router A to verify the multipath routes that are advertised and the associated traffic share values:
RouterA# show ip route 192.168.1.0Routing entry for 192.168.1.0/24Known via "bgp 100", distance 200, metric 0Tag 200, type internalLast update from 172.168.1.1 00:01:43 agoRouting Descriptor Blocks:* 172.168.1.1, from 172.168.1.1, 00:01:43 agoRoute metric is 0, traffic share count is 13AS Hops 1, BGP network version 0Route tag 200172.168.2.2, from 172.168.2.2, 00:01:43 agoRoute metric is 0, traffic share count is 30AS Hops 1, BGP network version 0Route tag 200172.168.3.3, from 172.168.3.3, 00:01:43 agoRoute metric is 0, traffic share count is 120AS Hops 1, BGP network version 0Route tag 200Where to Go Next
For information about the BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN feature, refer to the following document:
http://www.cisco.com/en/US/docs/ios/iproute_bgp/configuration/guide/irg_ebgp_ibgp.html
For more information about the iBGP Multipath Load Sharing feature, refer to the following document:
http://www.cisco.com/en/US/docs/ios/iproute_bgp/configuration/guide/irg_multi_load.html
Additional References
The following sections provide references related to the BGP Link Bandwidth feature.
Related Documents
BGP commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples
BGP configuration tasks
BGP Feature Roadmap module
CEF configuration tasks
Standards
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
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MIBs
RFCs
Technical Assistance
Feature Information for BGP Link Bandwidth
Table 1 lists the features in this module and provides links to specific configuration information.
Note
Table 1 Feature Information for <Phrase Based on Module Title>
BGP Link Bandwidth
12.2(2)T
12.2(14)S
This feature advertises the bandwidth of an autonomous system exit link as an extended community. The link bandwidth extended community attribute is propagated to iBGP peers when extended community exchange is enabled.
The following sections provide information about this feature:
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The following commands were introduced or modified: router bgp, address-family ipv4, address-family ipv4, bgp dmzlink-bw, neighbor, show ip bgp, show ip route.
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Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.
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