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Table Of Contents
Related Features and Technologies
Configuring an Interface as a DSBM Candidate
Verifying Configuration of SBM State
SBM Candidate Configuration Examples
Subnetwork Bandwidth Manager
Feature Overview
Resource Reservation Protocol (RSVP) is a signalling mechanism that supports request of specific levels of service such as reserved bandwidth from the network. RSVP and its service class definitions are largely independent of the underlying network technologies. This independence requires that a user define the mapping of RSVP onto subnetwork technologies.
The Subnetwork Bandwidth Manager (SBM) feature answers this requirement for RSVP in relation to IEEE 802-based networks. SBM specifies a signalling method and protocol for LAN-based admission control for RSVP flows. SBM allows RSVP-enabled routers and Layer 2 and Layer 3 devices to support reservation of LAN resources for RSVP-enabled data flows. The SBM signalling method is similar to that of RSVP itself. SBM protocol entities have the following features:
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Reside in Layer 2 or Layer 3 devices.
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A managed segment includes those interconnected parts of a shared LAN that are not separated by DSBMs. The presence of a DSBM makes the segment a managed one. One or more SBMs may exist on a managed segment, but there can be only one DSBM on each managed segment.
You can configure an interface on routers connected to the segment to participate in the DSBM election process. The contender configured with the highest priority becomes the DSBM for the managed segment.
If you do not configure a router as a DSBM candidate and RSVP is enabled, then the system interacts with the DSBM if a DSBM is present on the segment. In fact, if a DSBM, identifying itself as such, exists on the segment, the segment is considered a managed segment and all RSVP message forwarding will be based on the SBM message forwarding rules. This behavior exists to allow cases in which you might not want an RSVP-enabled interface on a router connected to a managed segment interface to become a DSBM, but you want it to interact with the DSBM if one is present managing the segment.
shows a managed segment in an Layer 2 domain that interconnects a set of hosts and routers.
Figure 1 DSBM Managed Segment
When a DSBM client sends or forwards an RSVP PATH message over an interface attached to a managed segment, it sends the PATH message to the segment's DSBM instead of to the RSVP session destination address, as is done in conventional RSVP processing. As part of its message processing procedure, the DSBM builds and maintains a PATH state for the session and notes the previous Layer 2/Layer 3 hop from which it received the PATH message. After processing the PATH message, the DSBM forwards it toward its destination address.
The DSBM receives the RSVP reservation request (RSVP RESV) message and processes it in a manner similar to how RSVP itself handles reservation request processing, basing the outcome on available bandwidth. The procedure is as follows:
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Benefits
The SBM feature enables admission control over IEEE 802-styled networks.
Restrictions
SBM is not supported currently on Token Ring LANs.
Related Features and Technologies
The SBM feature is used in conjunction with RSVP, which is documented in the Quality of Service Solutions Configuration Guide and the Quality of Service Solutions Command Reference.
Related Documents
For related information on this feature, refer to the following documents:
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Supported Platforms
This feature runs on all platforms that also support RSVP beginning with Release 12.0(5)T.
Prerequisites
To use the SBM feature and enable an interface as a DSBM candidate, the user must enable RSVP on the interface.
Supported MIBs and RFCs
MIBs
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RFCs
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List of Terms and Acronyms
Designated Subnetwork Bandwidth Manager—See DSBM.
DSBM—A protocol entity that resides in a Layer 2 or Layer 3 device and manages resources on a Layer 2 segment. Only one, if any, DSBM exists for each Layer 2 segment.
DSBM clients—Entities that transmit traffic onto a managed segment and use the services of a DSBM for the managed segment for admission control over a LAN segment. DSBM clients are always Layer 3 entities because only Layer 3 (or higher) entities are expected to send traffic requiring resource reservations.
extended segment—Those parts of a network that are members of the same IP subnet and are not separated by any Layer 3 devices. Several managed segments interconnected by Layer 2 devices constitute an extended segment.
Layer 2—Also referred to as the link layer of the ISO seven-layer model, comprises data link layer technologies such as IEEE 802.3 Ethernet.
Layer 2 devices—Devices that implement only Layer 2 functionality. These devices include 802.1D bridges and switches.
Layer 3—Network layer of the ISO seven-layer model. SBM primarily pertains to networks that use the IP at this layer.
Layer 3 devices—Also known as Layer 3 devices or end stations, these devices include hosts and routers that use Layer 3 and higher layer protocols or application programs that make resource reservations.
managed Layer 2 domain—A Layer 2 domain consisting of managed segments. A managed Layer 2 domain includes a DSBM that exercises admission control over resources at segments in the Layer 2 domain.
managed segment—A segment with a DSBM present that is responsible for exercising admission control over requests for resource reservations. A managed segment includes those interconnected parts of a shared LAN that are not separated by DSBMs.
SBM—A protocol entity that resides in a Layer 2 or Layer 3 device and can manage resources on a segment. When more than one SBM exists on a segment, one of the SBMs is elected to be the DSBM.
SBM transparent device—A device that is unaware of SBMs or DSBMs and therefore does not participate in the SBM-based admission control procedure over a managed segment. An SBM transparent device may or may not be RSVP aware.
segment—A Layer 2 physical segment that is shared by one or more senders, such as a shared Ethernet or Token Ring wire resolving contention for media access using CSMA or token passing.
subnet—In regard to SBM, a group of Layer 3 devices sharing a common Layer 3 network address prefix along with the set of segments making up the Layer 2 domain in which they are located.
Subnetwork Bandwidth Manager—See SBM.
traffic class—An aggregation of data flows that are given similar service within a switched network.
Configuration Tasks
To configure SBM, perform the following task:
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Configuring an Interface as a DSBM Candidate
SBM is used in conjunction with RSVP. Therefore, before you configure an interface as a DSBM contender, ensure that RSVP is enabled on that interface. To enable RSVP on an interface, use the following interface configuration command:
Verifying Configuration of SBM State
To display information that enables you to determine if an interface has been configured as a DSBM candidate and which of the contenders has been elected the DSBM, use the following command in EXEC mode:
Displays information about an SBM configured for a specific RSVP-enabled interface or for all RSVP-enabled interfaces on the router.
The command output identifies the interface by name and IP address, and it shows whether the interface has been configured as a DSBM contender. If the interface is a contender, the DSBM Priority field displays its priority. The DSBM election process is dynamic, addressing any new contenders configured as participants. Consequently, at any given time, an incumbent DSBM might be replaced by one configured with a higher priority.
router1# show ip rsvp sbmInterface DSBM Addr DSBM Priority DSBM Candidate My PriorityEt1 1.1.1.1 70 yes 70Et2 145.2.2.150 100 yes 100
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SBM Candidate Configuration Examples
In the following example, RSVP and SBM are enabled on an Ethernet2 interface. After RSVP is enabled, the interface is configured as a DSBM and SBM candidate with a priority of 100. The configured priority is high, making this interface a good contender for DSBM status. However, the maximum configurable priority value is 128, so another interface configured with a higher priority could win the election and become the DSBM.
interface Ethernet2ip address 145.2.2.150 255.255.255.0no ip directed-broadcastip pim sparse-dense-modeno ip mroute-cachemedia-type 10BaseTip rsvp bandwidth 7500 7500ip rsvp dsbm-candidate 100endCommand Reference
This section documents the following new commands. All other commands used with this feature are documented in the Cisco IOS Release 12.0 command references.
ip rsvp bandwidth
To enable Resource Reservation Protocol (RSVP) and Subnetwork Bandwidth Manager (SBM) for IP on an interface, use the ip rsvp bandwidth interface configuration command. To disable RSVP and SBM on an interface, use the no form of this command.
ip rsvp bandwidth [interface-kbps [single-flow-kbps]]
no ip rsvp bandwidth [interface-kbps [single-flow-kbps]]Syntax Description
Defaults
RSVP is disabled. If this command is entered without the optional arguments, RSVP is enabled on 75 percent of the link bandwidth.
Command Modes
Interface configuration
Command History
11.2
This command was introduced.
12.0(5)T
This command was revised to support SBM.
Usage Guidelines
This command is not supported on Versatile Interface Processor-based routers. RSVP is disabled by default to allow backward compatibility with systems that do not implement RSVP. Weighted Random Early Detection (WRED) or fair queueing must be enabled first.
Examples
The following example shows a T1 (1536 kbps) link configured to permit RSVP reservation of up to 1158 kbps, but no more than 100 kbps for any given flow on serial interface 0. Fair queueing is configured with 15 reservable queues to support those reserved flows, should they be required.
router(config)# interface serial 0 router(config-if)# fair-queue 64 256 15 router(config-if)# ip rsvp bandwidth 1158 100Related Commands
ip rsvp dsbm-candidate
To configure an interface as a Designated Subnetwork Bandwidth Manager (DSBM) candidate, use the ip rsvp dsbm-candidate interface configuration command. To disable DSBM on an interface, which exempts the interface as a DSBM candidate, use the no form of this command.
ip rsvp dsbm-candidate [priority]
no ip rsvp dsbm-candidateSyntax Description
priority
(Optional) A value in the range of 64 to 128. Among contenders for the DSBM, the interface with the highest priority number wins the DSBM election process.
Defaults
An interface is not configured as a DSBM contender by default. If you use this command to enable the interface as a DSBM candidate and you do not specify a priority, the default priority of 64 is assumed.
Command Modes
Interface configuration
Command History
Usage Guidelines
SBM protocol entities, any one of which can manage resources on a segment, can reside in Layer 2 or Layer 3 devices. Many SBM-capable devices may be attached to a shared Layer 2 segment. When more than one SBM exists on a given segment, one of the SBMs is elected to be the DSBM. The elected DSBM is responsible for exercising admission control over requests for resource reservations on a segment, which, in the process, becomes a managed segment. A managed segment includes those interconnected parts of a shared LAN that are not separated by DSBMs. In all circumstances, only one, if any, DSBM exists for each Layer 2 segment.
You can configure an interface to have a DSBM priority in the range of 64 to 128. You can exempt an interface from participation in the DSBM election on a segment but still allow the system to interact with the DSBM if a DSBM is present on the segment. In other words, you can allow an RSVP-enabled interface on a router connected to a managed segment to be managed by the DSBM even if you do not configure that interface to participate as a candidate in the DSBM election process. To exempt an interface from DSBM candidacy, do not issue the ip rsvp dsbm-candidate command on that interface.
Examples
The following example configures interface Ethernet2 as a DSBM candidate with a priority of 100:
interface Ethernet2ip rsvp dsbm-candidate 100Related Commands
show ip rsvp sbm
Displays information about an SBM configured for a specific RSVP-enabled interface or for all RSVP-enabled interfaces on the router.
show ip rsvp sbm
To display information about a Subnetwork Bandwidth Manager (SBM) configured for a specific Resource Reservation Protocol (RSVP) enabled interface or for all RSVP-enabled interfaces on the router, use the show ip rsvp sbm interface command.
show ip rsvp sbm [interface-name]
Syntax Description
interface-name
(Optional) Name of the interface for which you want to display SBM configuration information.
Command Modes
EXEC
Command History
Usage Guidelines
To obtain SBM configuration information about a specific interface configured to use RSVP, specify the interface name with the show ip rsvp sbm command. To obtain information about all interfaces enabled for RSVP on the router, use the show ip rsvp sbm command without specifying an interface name.
Examples
The following example displays information for the two RSVP-enabled Ethernet interfaces Et1 and Et2 on router1:
router# show ip rsvp sbmInterface DSBM Addr DSBM Priority DSBM Candidate My PriorityEt1 1.1.1.1 70 yes 70Et2 145.2.2.150 100 yes 100The following example displays information about the RSVP-enabled Ethernet interface e2 on router1:
router# show ip rsvp sbm e2Interface DSBM Addr DSBM Priority DSBM candidate My Prioritye2 145.2.2.150 100 yes 100identifies the fields and their values displayed as output of the show ip rsvp sbm command.
Related Commands
Debug Commands
This section documents new Cisco IOS Release 12.0(5)T debug commands related to SBM. All other commands used with this feature are documented in the Cisco IOS Release 12.0 Quality of Service Solutions Command Reference publication.
debug ip rsvp
To display information about Subnetwork Bandwidth Manager (SBM) message processing, the Designated Subnetwork Bandwidth Manager (DSBM) election process, and standard Resource Reservation Protocol RSVP enabled message processing information, use the debug ip rsvp privileged EXEC command. To turn off ip rsvp debugging when you no longer want to display the output, use the no form of this command.
debug ip rsvp
no debug ip rsvpSyntax Description
This command has no arguments or keywords.
Default
This command is disabled by default.
Usage Guidelines
The debug ip rsvp command provides information about messages received, minimal detail about the content of these messages, and information about state transitions. To obtain detailed information about RSVP and SBM, use the debug ip rsvp detail command.
Command History
Examples
The following example enables output of debug information about SBM message processing, the DSBM election process, and RSVP message processing information on router2:
router# debug ip rsvpRSVP debugging is onrouter2#*Dec 31 16:42:14.635: RSVP: send I_AM_DSBM message from 145.2.2.150*Dec 31 16:42:14.635: RSVP: IP to 224.0.0.17 length=88 checksum=C788 Ethernet2)*Dec 31 16:42:19.635: RSVP: send I_AM_DSBM message from 145.2.2.150*Dec 31 16:42:19.635: RSVP: IP to 224.0.0.17 length=88 checksum=C788 (Ethernet2)*Dec 31 16:42:20.823: RSVP: PATH message for 145.5.5.202(Ethernet2) from 145.2.2.1*Dec 31 16:42:22.163: RSVP: send path multicast about 145.5.5.202 on Ethernet2*Dec 31 16:42:22.163: RSVP: DSBM mgd segment - sending to ALLSBMADDRESS*Dec 31 16:42:22.163: RSVP: IP to 224.0.0.17 length=212 checksum=DCAB (Ethernet2)*Dec 31 16:42:23.955: RSVP: Sending RESV message for 145.5.5.202*Dec 31 16:42:23.955: RSVP: send reservation to 145.2.2.1 about 145.5.5.202*Dec 31 16:42:23.955: RSVP: IP to 145.2.2.1 length=108 checksum=1420 (Ethernet2)*Dec 31 16:42:24.443: RSVP: RESV message for 145.5.5.202 (Ethernet2) from 145.2.2.2*Dec 31 16:42:24.635: RSVP: send I_AM_DSBM message from 145.2.2.150*Dec 31 16:42:24.635: RSVP: IP to 224.0.0.17 length=88 checksum=43AF (Ethernet2)Related Commands
debug ip rsvp detail
To display detailed information about Resource Reservation Protocol RSVP enabled and Subnetwork Bandwidth Manager (SBM), use the debug ip rsvp detail privileged EXEC command. To turn off ip rsvp debugging when you no longer want to display the output, use the no form of this command.
debug ip rsvp detail
no debug ip rsvp detailSyntax Description
This command has no arguments or keywords.
Defaults
This command is disabled by default.
Command History
Examples
The following example shows the detailed debug information about RSVP and SBM that is available when you enable debug mode through the debug ip rsvp detail command:router# debug ip rsvp detailRSVP debugging is onrouter2#u*Dec 31 16:44:29.651: RSVP: send I_AM_DSBM message from 145.2.2.150*Dec 31 16:44:29.651: RSVP: IP to 224.0.0.17 length=88 checksum=43AF (Ethernet2)*Dec 31 16:44:29.651: RSVP: version:1 flags:0000 type:I_AM_DSBM cksum:43AF ttl:254 reserved:0 length:88*Dec 31 16:44:29.651: DSBM_IP_ADDR type 1 length 8 : 91020296*Dec 31 16:44:29.651: HOP_L2 type 1 length 12: 00E01ECE*Dec 31 16:44:29.651: : 0F760000*Dec 31 16:44:29.651: SBM_PRIORITY type 1 length 8 : 00000064*Dec 31 16:44:29.651: DSBM_TIMERS type 1 length 8 : 00000F05*Dec 31 16:44:29.651: SBM_INFO type 1 length 44: 00000000*Dec 31 16:44:29.651: : 00240C02 00000007*Dec 31 16:44:29.651: : 01000006 7F000005*Dec 31 16:44:29.651: : 00000000 00000000*Dec 31 16:44:29.655: : 00000000 00000000*Dec 31 16:44:29.655: : 00000000Related Commands
debug ip rsvp detail sbm
To display detailed information about Subnetwork Bandwidth Manager (SBM) messages only, and SBM and Designated Subnetwork Bandwidth Manager (DSBM) state transitions, use the debug ip rsvp detail sbm privileged EXEC command. To turn off ip rsvp debugging when you no longer want to display the output, use the no form of this command.
debug ip rsvp detail sbm
no debug ip rsvp detail sbmSyntax Description
This command has no arguments or keywords.
Defaults
This command is disabled by default.
Usage Guidelines
The debug ip rsvp detail sbm command provides information about messages received, minimal detail about the content of these messages, and information about state transitions.
Command History
Examples
The following example shows the detailed debug information about SBM and the SBM and DSBM state transitions that is available when you enable debug mode through the debug ip rsvp detail sbm command:router# debug ip rsvp detail sbmRSVP debugging is onrouter2#*Dec 31 16:45:34.659: RSVP: send I_AM_DSBM message from 145.2.2.150*Dec 31 16:45:34.659: RSVP: IP to 224.0.0.17 length=88 checksum=9385 (Ethernet2)*Dec 31 16:45:34.659: RSVP: version:1 flags:0000 type:I_AM_DSBM cksum:9385 ttl:254 reserved:0 length:88*Dec 31 16:45:34.659: DSBM_IP_ADDR type 1 length 8 : 91020296*Dec 31 16:45:34.659: HOP_L2 type 1 length 12: 00E01ECE*Dec 31 16:45:34.659: : 0F760000*Dec 31 16:45:34.659: SBM_PRIORITY type 1 length 8 : 0029B064*Dec 31 16:45:34.659: DSBM_TIMERS type 1 length 8 : 00000F05*Dec 31 16:45:34.659: SBM_INFO type 1 length 44: 00000000*Dec 31 16:45:34.659: : 00240C02 00000007*Dec 31 16:45:34.659: : 01000006 7F000005*Dec 31 16:45:34.659: : 00000000 00000000*Dec 31 16:45:34.663: : 00000000 00000000*Dec 31 16:45:34.663: : 00000000*Dec 31 16:45:34.663:Related Commands
