BGP Support for MTR
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Contents
BGP Support for MTRLast Updated: July 23, 2010
The BGP Support for MTR feature provides Border Gateway Protocol (BGP) support for multiple logical topologies over a single physical network. This module describes how to configure BGP for Multitopology Routing (MTR). Finding Feature InformationYour 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 Table at the end of this document. 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. Restrictions for BGP Support for MTR
Information About BGP Support for MTRRouting Protocol Support for MTRYou must enable IP routing on the router for MTR to operate. MTR supports static and dynamic routing in Cisco IOS software. You can enable dynamic routing per-topology to support inter-domain and intra-domain routing. Route calculation and forwarding are independent for each topology. MTR support is integrated into Cisco IOS software for the following protocols:
You apply the per-topology configuration in router address family configuration mode of the global routing process (router configuration mode). The address family and subaddress family are specified when entering address-family configuration mode. You specify the topology name and topology ID by entering the topology command in address-family configuration mode. You configure each topology with a unique topology ID under the routing protocol. The topology ID is used to identify and group NLRI for each topology in updates for a given protocol. In OSPF, EIGRP, and IS-IS, you enter the topology ID during the first configuration of the topology command for a class-specific topology. In BGP, you configure the topology ID by entering the bgp tid command under the topology configuration. You can configure class-specific topologies with different metrics than the base topology. Interface metrics configured on the base topology can be inherited by the class-specific topology. Inheritance occurs if no explicit inheritance metric is configured in the class-specific topology. You configure BGP support only in router configuration mode. You configure Interior Gateway Protocol (IGP) support in router configuration mode and in interface configuration mode. By default, interfaces are not included in non-base topologies. For routing protocol support for EIGRP, IS-IS, and OSPF, you must explicitly configure a non-base topology on an interface. You can override the default behavior by using the all-interfaces command in address family topology configuration mode. The all-interfaces command causes the non-base topology to be configured on all interfaces of the router that are part of the default address space or the VRF in which the topology is configured. BGP Network ScopeTo implement MTR for BGP, the scope hierarchy is required, but the scope hierarchy is not limited to MTR use. The scope hierarchy introduces some new configuration modes such as router scope configuration mode. You enter router scope configuration mode by configuring the scope command in router configuration mode. When this command is entered, a collection of routing tables is created. You configure BGP commands under the scope hierarchy for a single network (globally), or on a per-VRF basis, and are referred to as scoped commands. The scope hierarchy can contain one or more address families. MTR CLI Hierarchy Under BGPThe BGP CLI provides backward compatibility for pre-MTR BGP configuration and provides a hierarchical implementation of MTR. Router configuration mode is backward compatible with the pre-address family and pre-MTR configuration CLI. Global commands that affect all networks are configured in this configuration mode. For address-family and topology configuration, you configure general session commands and peer templates to be used in the address-family or in the topology configuration mode. After configuring any global commands, you define the scope either globally or for a specific VRF. You enter address family configuration mode by configuring the address-family command in router scope configuration mode or in router configuration mode. Unicast is the default address family if no subaddress family (SAFI) is specified. MTR supports only the IPv4 address family with a SAFI of unicast or multicast. Entering address family configuration mode from router configuration mode configures BGP to use pre-MTR-based CLI. This configuration mode is backward compatible with pre-existing address family configurations. Entering address family configuration mode from router scope configuration mode configures the router to use the hierarchical CLI that supports MTR. Address family configuration parameters that are not specific to a topology are entered in this address family configuration mode. You enter BGP topology configuration mode by configuring the topology (BGP) command in address family configuration mode. You can configure up to 32 topologies (including the base topology) on a router. You configure the topology ID by entering the bgp tid command. All address family and subaddress family configuration parameters for the topology are configured here.
The following example shows the hierarchy levels that are used when configuring BGP for MTR implementation: router bgp <autonomous-system-number> ! Global commands scope {global | vrf <vrf-name>} ! Scoped commands address-family {<afi>} [<safi>] ! Address family specific commands topology {<topology-name> | base} ! topology specific commands For detailed steps, see the Activating an MTR Topology by Using BGP section. BGP Sessions for Class-Specific TopologiesMTR is configured under BGP on a per-session basis. The base unicast and multicast topologies are carried in the global (default) session. A separate session is created for each class-specific topology that is configured under a BGP routing process. Each session is identified by its topology ID. BGP performs a best-path calculation individually for each class-specific topology. A separate RIB and FIB are maintained for each session. Topology Translation Using BGPDepending on the design and policy requirements for your network, you might need to install routes from a class-specific topology on one router in a class-specific topology on a neighboring router. Topology translation functionality using BGP provides support for this operation. Topology translation is BGP neighbor-session based. You configure the neighbor translate-topology command by using the IP address and topology ID from the neighbor. The topology ID identifies the class-specific topology of the neighbor. The routes in the class-specific topology of the neighbor are installed in the local class-specific RIB. BGP performs a best-path calculation on all installed routes and installs these routes into the local class-specific RIB. If a duplicate route is translated, BGP selects and installs only one instance of the route per standard BGP best-path calculation behavior. Topology Import Using BGPTopology import functionality using BGP is similar to topology translation. The difference is that routes are moved between class-specific topologies on the same router by using BGP. You configure this function by entering the import topology command and specify the name of the class-specific topology or base topology. Best-path calculations are run on the imported routes before they are installed into the topology RIB. This command also includes a route-map keyword to allow you to filter routes that are moved between class-specific topologies. For detailed steps, see the Importing Routes from an MTR Topology by Using BGP section. How to Configure BGP Support for MTRActivating an MTR Topology by Using BGPPerform this task to activate an MTR topology inside an address family by using BGP. This task is configured on Router B in the figure below and must also be configured on Router D and Router E. In this task, a scope hierarchy is configured to apply globally, and a neighbor is configured under router scope configuration mode. Under the IPv4 unicast address family, an MTR topology that applies to video traffic is activated for the specified neighbor. There is no interface configuration mode for BGP topologies. Before You Begin
SUMMARY STEPS
DETAILED STEPS What to Do NextRepeat this task for every topology that you want to enable, and repeat this configuration on all neighbor routers that are to use the topologies. If you want to import routes from one MTR topology to another on the same router, proceed to the Importing Routes from an MTR Topology by Using BGP section. Importing Routes from an MTR Topology by Using BGPBefore You Begin
SUMMARY STEPS
DETAILED STEPS
Configuration Examples for BGP Support for MTRExample BGP Topology Translation ConfigurationThe following example shows how to configure BGP in the VIDEO topology and how to configure topology translation with the 192.168.2.2 neighbor: router bgp 45000 scope global neighbor 172.16.1.1 remote-as 50000 neighbor 192.168.2.2 remote-as 55000 neighbor 172.16.1.1 transport multi-session neighbor 192.168.2.2 transport multi-session address-family ipv4 topology VIDEO bgp tid 100 neighbor 172.16.1.1 activate neighbor 192.168.2.2 activate neighbor 192.168.2.2 translate-topology 200 end clear ip bgp topology VIDEO 50000 Example BGP Scope Global and VRF ConfigurationThe following example shows how to configure a global scope for a unicast topology and also for a multicast topology. After exiting the router scope configuration mode, a scope is configured for the VRF named DATA. router bgp 45000 scope global bgp default ipv4-unicast neighbor 172.16.1.2 remote-as 45000 neighbor 192.168.3.2 remote-as 50000 address-family ipv4 unicast topology VOICE bgp tid 100 neighbor 172.16.1.2 activate exit address-family ipv4 multicast topology base neighbor 192.168.3.2 activate exit exit exit scope vrf DATA neighbor 192.168.1.2 remote-as 40000 address-family ipv4 neighbor 192.168.1.2 activate end Example BGP Topology VerificationThe following example shows summary output for the show ip bgp topology command. Information is displayed about BGP neighbors configured to use the MTR topology named VIDEO.
Router# show ip bgp topology VIDEO summary
BGP router identifier 192.168.3.1, local AS number 45000
BGP table version is 1, main routing table version 1
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
172.16.1.2 4 45000 289 289 1 0 0 04:48:44 0
192.168.3.2 4 50000 3 3 1 0 0 00:00:27 0
The following partial output displays BGP neighbor information under the VIDEO topology:
Router# show ip bgp topology VIDEO neighbors 172.16.1.2
BGP neighbor is 172.16.1.2, remote AS 45000, internal link
BGP version 4, remote router ID 192.168.2.1
BGP state = Established, up for 04:56:30
Last read 00:00:23, last write 00:00:21, hold time is 180, keepalive interval is 60
seconds
Neighbor sessions:
1 active, is multisession capable
Neighbor capabilities:
Route refresh: advertised and received(new)
Message statistics, state Established:
InQ depth is 0
OutQ depth is 0
Sent Rcvd
Opens: 1 1
Notifications: 0 0
Updates: 0 0
Keepalives: 296 296
Route Refresh: 0 0
Total: 297 297
Default minimum time between advertisement runs is 0 seconds
For address family: IPv4 Unicast topology VIDEO
Session: 172.16.1.2 session 1
BGP table version 1, neighbor version 1/0
Output queue size : 0
Index 1, Offset 0, Mask 0x2
1 update-group member
Topology identifier: 100
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Address tracking is enabled, the RIB does have a route to 172.16.1.2
Address tracking requires at least a /24 route to the peer
Connections established 1; dropped 0
Last reset never
Transport(tcp) path-mtu-discovery is enabled
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
Minimum incoming TTL 0, Outgoing TTL 255
Local host: 172.16.1.1, Local port: 11113
Foreign host: 172.16.1.2, Foreign port: 179
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Example Importing Routes from an MTR Topology by Using BGPThe following example shows how to configure an access list to be used by a route map named BLUE to filter routes imported from the MTR topology named VOICE. Only routes with the prefix 192.168.1.0 are imported. access-list 1 permit 192.168.1.0 0.0.0.255 route-map BLUE match ip address 1 exit router bgp 50000 scope global neighbor 10.1.1.2 remote-as 50000 neighbor 172.16.1.1 remote-as 60000 address-family ipv4 topology VIDEO bgp tid 100 neighbor 10.1.1.2 activate neighbor 172.16.1.1 activate import topology VOICE route-map BLUE end clear ip bgp topology VIDEO 50000 Additional ReferencesRelated DocumentsTechnical Assistance
Feature Information for BGP Support for MTRThe 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.
Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at www.cisco.com/go/trademarks. Third party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1005R) Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental. © 2007-2012 Cisco Systems, Inc. All rights reserved.
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