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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 BGP Link Bandwidth
Verifying BGP Link Bandwidth Configuration
Configuration Examples for BGP Link Bandwidth
BGP Link Bandwidth Configuration Example
BGP Link Bandwidth
The Border Gateway Protocol (BGP) 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.
History for the BGP Link Bandwidth Feature
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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
To configure the BGP Link Bandwidth feature, you must understand the following concept:
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BGP Link Bandwidth Overview
The BGP Link Bandwidth feature used to enable multipath load balancing for external links with unequal bandwidth capacity. This feature is enabled under an IPv4 or VPNv4 address family sessions by entering the bgp dmzlink-bw command. This feature supports both iBGP, eBGP multipath load balancing, and eiBGP multipath load balancing in Multiprotocol Label Switching (MPLS) Virtual Private Networks (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 that 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 forwarding traffic. 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
This section contains the following procedures:
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Configuring BGP Link Bandwidth
To configure the BGP Link Bandwidth feature, perform the steps in this section.
SUMMARY STEPS
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DETAILED STEPS
Verifying BGP Link Bandwidth Configuration
To verify the BGP Link Bandwidth feature, perform the steps in this section.
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DETAILED STEPS
Configuration Examples for BGP Link Bandwidth
The following examples show how to configure and verify this feature:
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BGP Link Bandwidth Configuration Example
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.
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:
Router A(config)# router bgp 100Router A(config-router)# neighbor 10.10.10.2 remote-as 100Router A(config-router)# neighbor 10.10.10.2 update-source Loopback 0Router A(config-router)# neighbor 10.10.10.3 remote-as 100Router A(config-router)# neighbor 10.10.10.3 update-source Loopback 0Router A(config-router)# address-family ipv4Router A(config-router)# bgp dmzlink-bwRouter A(config-router-af)# neighbor 10.10.10.2 activateRouter A(config-router-af)# neighbor 10.10.10.2 send-community bothRouter A(config-router-af)# neighbor 10.10.10.3 activateRouter A(config-router-af)# neighbor 10.10.10.3 send-community bothRouter A(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:
Router B(config)# router bgp 100Router B(config-router)# neighbor 10.10.10.1 remote-as 100Router B(config-router)# neighbor 10.10.10.1 update-source Loopback 0Router B(config-router)# neighbor 10.10.10.3 remote-as 100Router B(config-router)# neighbor 10.10.10.3 update-source Loopback 0Router B(config-router)# neighbor 172.16.1.1 remote-as 200Router B(config-router)# neighbor 172.16.1.1 ebgp-multihop 1Router B(config-router)# neighbor 172.16.2.2 remote-as 200Router B(config-router)# neighbor 172.16.2.2 ebgp-multihop 1Router B(config-router)# address-family ipv4Router B(config-router-af)# bgp dmzlink-bwRouter B(config-router-af)# neighbor 10.10.10.1 activateRouter B(config-router-af)# neighbor 10.10.10.1 next-hop-selfRouter B(config-router-af)# neighbor 10.10.10.1 send-community bothRouter B(config-router-af)# neighbor 10.10.10.3 activateRouter B(config-router-af)# neighbor 10.10.10.3 next-hop-selfRouter B(config-router-af)# neighbor 10.10.10.3 send-community bothRouter B(config-router-af)# neighbor 172.16.1.1 activateRouter B(config-router-af)# neighbor 172.16.1.1 dmzlink-bwRouter B(config-router-af)# neighbor 172.16.2.2 activateRouter B(config-router-af)# neighbor 172.16.2.2 dmzlink-bwRouter B(config-router-af)# maximum-paths ibgp 6Router B(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:
Router C(config)# router bgp 100Router C(config-router)# neighbor 10.10.10.1 remote-as 100Router C(config-router)# neighbor 10.10.10.1 update-source Loopback 0Router C(config-router)# neighbor 10.10.10.2 remote-as 100Router C(config-router)# neighbor 10.10.10.2 update-source Loopback 0Router C(config-router)# neighbor 172.16.3.30 remote-as 200Router C(config-router)# neighbor 172.16.3.30 ebgp-multihop 1Router C(config-router)# address-family ipv4Router C(config-router-af)# bgp dmzlink-bwRouter C(config-router-af)# neighbor 10.10.10.1 activateRouter C(config-router-af)# neighbor 10.10.10.1 send-community bothRouter C(config-router-af)# neighbor 10.10.10.1 next-hop-selfRouter C(config-router-af)# neighbor 10.10.10.2 activateRouter C(config-router-af)# neighbor 10.10.10.2 send-community bothRouter C(config-router-af)# neighbor 10.10.10.2 next-hop-selfRouter C(config-router-af)# neighbor 172.16.3.3 activateRouter C(config-router-af)# neighbor 172.16.3.3 dmzlink-bwRouter C(config-router-af)# maximum-paths ibgp 6Router C(config-router-af)# maximum-paths 6Verifying BGP Link Bandwidth
The examples in this section show the verification of this feature on Router A and Router B.
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.
Router B# 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. The output shows that a route for each exit link (on Router B and Router C) to autonomous system 200 has been installed as a best path in the BGP routing table.
Router A# 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:
Router A# 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/configuration/guide/irp_bgp_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/configuration/guide/irp_bgp_multi_load.html
Additional References
The following sections provide references related to BGP Link Bandwidth feature.
Related Documents
BGP commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples
BGP configuration tasks
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
Command Reference
The following commands are introduced or modified in the feature or features documented in this module. For information about these commands, see the Cisco IOS IP Routing Protocols Command Reference at http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_book.html. For information about all Cisco IOS commands, go to the Command Lookup Tool at http://tools.cisco.com/Support/CLILookup or to the Cisco IOS Master Commands List.
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