Wide-Area Networking Configuration Guide: Frame Relay, Cisco IOS Release 15S
Distributed Multilink Frame Relay FRF.16
Distributed Multilink Frame Relay FRF.16
Last Updated: November 26, 2012
This document describes the Distributed Multilink Frame Relay (dMFR) feature in Cisco IOS Release 12.0(24)S and Cisco IOS Release 12.3(4)T. The dMFR feature introduces MFR on VIP-enabled Cisco 7500 series routers. For information on MFR on other platforms, see the Multilink Frame Relay (FRF.16) document.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and 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 module.
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.
The Distributed Multilink Frame Relay feature introduces functionality based on the Frame Relay Forum Multilink Frame Relay UNI/NNI Implementation Agreement (FRF.16) to VIP-enabled Cisco 7500 series routers. The Distributed Multilink Frame Relay feature provides a cost-effective way to increase bandwidth for particular applications by enabling multiple serial links to be aggregated into a single bundle of bandwidth. Multilink Frame Relay is supported on User-to-Network Interfaces (UNI) and Network-to-Network Interfaces (NNI) in Frame Relay networks.
Multilink Frame Relay Bundles and Bundle Links
The Multilink Frame Relay feature enables you to create a virtual interface called a bundle or bundle interface . The bundle interface emulates a physical interface for the transport of frames. The Frame Relay data link runs on the bundle interface, and Frame Relay virtual circuits are built upon it.
The bundle is made up of multiple serial links, called bundle links . Each bundle link within a bundle corresponds to a physical interface. Bundle links are invisible to the Frame Relay data-link layer, so Frame Relay functionality cannot be configured on these interfaces. Regular Frame Relay functionality that you want to apply to these links must be configured on the bundle interface. Bundle links are visible to peer devices. The local router and peer devices exchange link integrity protocol control messages to determine which bundle links are operational and to synchronize which bundle links should be associated with which bundles.
Link Integrity Protocol Control Messages
For link management, each end of a bundle link follows the MFR Link Integrity Protocol and exchanges link control messages with its peer (the other end of the bundle link). To bring up a bundle link, both ends of the link must complete an exchange of ADD_LINK and ADD_LINK_ACK messages. To maintain the link, both ends periodically exchange HELLO and HELLO_ACK messages. This exchange of hello messages and acknowledgments serve as a keepalive mechanism for the link. If a router is sending hello messages but not receiving acknowledgments, it will resend the hello message up to a configured maximum number of times. If the router exhausts the maximum number of retries, the bundle link line protocol is considered down (unoperational).
The bundle link interface's line protocol status is considered up (operational) when the peer device acknowledges that it will use the same link for the bundle. The line protocol remains up when the peer device acknowledges the hello messages from the local router.
The bundle interface's line status becomes up when at least one bundle link has its line protocol status up. The bundle interface's line status goes down when the last bundle link is no longer in the up state. This behavior complies with the class A bandwidth requirement defined in FRF.16.
The bundle interface's line protocol status is considered up when the Frame Relay data-link layer at the local router and peer device synchronize using the Local Management Interface (LMI), when LMI is enabled. The bundle line protocol remains up as long as the LMI keepalives are successful.
Distributed Multilink Frame Relay provides load balancing across the bundle links within a bundle. If a bundle link chosen for transmission happens to be busy transmitting a long packet, the load balancing mechanism can try another link, thus solving the problems seen when delay-sensitive packets have to wait.
Flexible Pool of Bandwidth
By combining multiple physical interfaces into a bundle, you can design a Frame Relay interface with more bandwidth than is available from any single physical interface. For example, many new network applications require more bandwidth than is available on a T1 line. One option is to invest in a T3 line; however, T3 lines can be expensive and are not available in some locations. Distributed Multilink Frame Relay provides a cost-effective solution to this problem by allowing multiple T1 lines to be aggregated into a single bundle of bandwidth.
The Distributed Multilink Frame Relay feature has the following restrictions:
This feature works on the following port adapters:
Determining Platform Support Through Cisco Feature Navigator
Cisco IOS software is packaged in feature sets that are supported on specific platforms. To get updated information regarding platform support for this feature, access Cisco Feature Navigator. Cisco Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature.
Cisco Feature Navigator is a web-based tool that enables you to determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image. You can search by feature or release. Under the release section, you can compare releases side by side to display both the features unique to each software release and the features in common.
To access Cisco Feature Navigator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to email@example.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions found at this URL:
Cisco Feature Navigator is updated regularly when major Cisco IOS software releases and technology releases occur. For the most current information, go to the Cisco Feature Navigator home page at the following URL:
Availability of Cisco IOS Software Images
Platform support for particular Cisco IOS software releases is dependent on the availability of the software images for those platforms. Software images for some platforms may be deferred, delayed, or changed without prior notice. For updated information about platform support and availability of software images for each Cisco IOS software release, refer to the online release notes or, if supported, Cisco Feature Navigator.
Supported Standards MIBs and RFCs
No new or modified MIBs are supported by this feature.
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
If Cisco MIB Locator does not support the MIB information that you need, you can also obtain a list of supported MIBs and download MIBs from the Cisco MIBs page at the following URL:
To access Cisco MIB Locator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to firstname.lastname@example.org. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions found at this URL:
Configuring a Multilink Frame Relay Bundle
To configure the bundle interface for Distributed Multilink Frame Relay, use the following commands beginning in global configuration mode:
1. Router(config)# interface mfr number
2. Router(config-if)# frame-relay multilink bid name
Configuring a Multilink Frame Relay Bundle Link
To configure a bundle link interface for multilink Frame Relay, use the following commands beginning in global configuration mode:
1. Router(config)# interface serial number
2. Router(config-if)# encapsulation frame-relay mfr number[name]
3. Router(config-if)# frame-relay multilink lid name
4. Router(config-if)# frame-relay multilink hello seconds
5. Router(config-if)# frame-relay multilink ack seconds
6. Router(config-if)# frame-relay multilink retry number
Verifying Multilink Frame Relay
To verify multilink Frame Relay configuration, use the show frame-relay multilink command.
The following example shows output for the show frame-relay multilink command. Because a particular bundle or bundle link is not specified, information for all bundles and bundle links is displayed.
Router# show frame-relay multilink Bundle: MFR0, state up, class A, no fragmentation ID: Bundle-Dallas Serial5/1, state up/up, ID: BL-Dallas-1 Serial5/3, state up/add-sent, ID: BL-Dallas-3 Bundle: MFR1, state down, class B, fragmentation ID: Bundle-NewYork#1 Serial3/0, state up/up, ID: BL-NewYork-1 Serial3/2, state admin-down/idle, ID: BL-NewYork-2
The following example shows output for the show frame-relay multilink command with the serial number option. It displays information about the specified bundle link.
Router# show frame-relay multilink serial3/2 Bundle links : Serial3/2, HW state :Administratively down, Protocol state :Down_idle, LID :Serial3/2 Bundle interface = MFR0, BID = MFR0
The following examples show output for the show frame-relay multilink command with the serial number and detail options. Detailed information about the specified bundle links is displayed. The first example shows a bundle link in the "idle" state. The second example shows a bundle link in the "up" state.
Router# show frame-relay multilink serial3 detail Bundle links: Serial3, HW state = up, link state = Idle, LID = Serial3 Bundle interface = MFR0, BID = MFR0 Cause code = none, Ack timer = 4, Hello timer = 10, Max retry count = 2, Current count = 0, Peer LID = Serial5/3, RTT = 0 ms Statistics: Add_link sent = 0, Add_link rcv'd = 10, Add_link ack sent = 0, Add_link ack rcv'd = 0, Add_link rej sent = 10, Add_link rej rcv'd = 0, Remove_link sent = 0, Remove_link rcv'd = 0, Remove_link_ack sent = 0, Remove_link_ack rcv'd = 0, Hello sent = 0, Hello rcv'd = 0, Hello_ack sent = 0, Hello_ack rcv'd = 0, outgoing pak dropped = 0, incoming pak dropped = 0 Router# show frame-relay multilink serial3 detail Bundle links: Serial3, HW state = up, link state = Up, LID = Serial3 Bundle interface = MFR0, BID = MFR0 Cause code = none, Ack timer = 4, Hello timer = 10, Max retry count = 2, Current count = 0, Peer LID = Serial5/3, RTT = 4 ms Statistics: Add_link sent = 1, Add_link rcv'd = 20, Add_link ack sent = 1, Add_link ack rcv'd = 1, Add_link rej sent = 19, Add_link rej rcv'd = 0, Remove_link sent = 0, Remove_link rcv'd = 0, Remove_link_ack sent = 0, Remove_link_ack rcv'd = 0, Hello sent = 0, Hello rcv'd = 1, Hello_ack sent = 1, Hello_ack rcv'd = 0, outgoing pak dropped = 0, incoming pak dropped = 0
Monitoring and Maintaining Distributed Multilink Frame Relay
To monitor and maintain Distributed Multilink Frame Relay, use one or more of the following commands in privileged EXEC mode:
Distributed Multilink Frame Relay Configuration Example
The following example shows the configuration of bundle "MFR1". Serial interfaces 5/0 and 6/0 are configured as bundle links.
interface MFR1 frame-relay multilink bid first-bundle frame-relay traffic-shaping frame-relay class ocean interface MFR1.1 point-to-point ip address 18.104.22.168 255.255.255.0 frame-relay interface-dlci 100 interface Serial5/0 encapsulation frame-relay MFR1 frame-relay multilink lid first-link frame-relay multilink hello 9 frame-relay multilink retry 3 interface Serial6/0 encapsulation frame-relay MFR1 frame-relay multilink ack 4
BID --bundle identification. BID is the name used to identify the bundle. The BID can be assigned or the default can be used.
bundle --A logical grouping of one or more physical interfaces using the formats and procedures of multilink Frame Relay. A bundle emulates a physical interface to the Frame Relay data-link layer. The bundle is also referred to as the mfr interface .
bundle link --An individual physical interface that is a member of a bundle.
DLCI --data-link connection identifier. Value that identifies a permanent virtual circuit (PVC) in Frame Relay network.
HELLO message --Message that notifies a peer endpoint that the local endpoint is in the operational state (up).
HELLO_ACK --Message that notifies a peer endpoint that a hello message has been received.
LID --link identification. LID is the name used to identify a bundle link. The LID can be assigned or the default can be used.
LMI --Local Management Interface. Set of enhancements to the basic Frame Relay specification. LMI includes support for a keepalive mechanism, which verifies that data is flowing; a multicast mechanism, which provides the network server with its local DLCI and the multicast DLCI; global addressing, which gives DLCIs global rather than local significance in Frame Relay networks; and a status mechanism, which provides an ongoing status report on the DLCIs known to the switch.
NNI --Network-to-Network Interface. The interface between two Frame Relay devices that are both located in a private network or both located in a public network.
UNI --User-to-Network Interface. The interface between a Frame Relay device in a public network and a Frame Relay device in a private network.
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