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7/29/2019 S07 - IP QoS - Signaling Mechnisms.pdf
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7
Signaling Mechanism
Overview
The module describes RSVP as the signaling mechanism used in QoS enabled
networks. The module builds on knowledge about the IntServ model with the
addition of Common Open Policy Service (COPS) discussed in the introductory
module.
Objectives
Upon completion of this module, you will be able to perform the following tasks:
n Describe Resource Reservation Protocol (RSVP).
n Configure RSVP.
n Describe and configure RSVP on shared media using Subnet Bandwidth
Management (SBM).
n Monitor and troubleshoot RSVP.
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7-2 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
Resource Reservation Protocol (RSVP)
Overview
The section introduces Resource Reservation Protocol (RSVP) as the signaling
mechanism in QoS-enabled networks using the Integrated Services model.
Objectives
Upon completion of this lesson, you will be able to perform the following tasks:
n Describe Resource Reservation Protocol (RSVP).
n Configure RSVP.
n Monitor and troubleshoot RSVP.
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Copyright 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism 7-3
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-5
Resource Reservation ProtocolResource Reservation Protocol
RSVP is a protocol used to reserve resources in apath between a source and a destination
RSVP signals all network devices that a certainapplication needs certain QoS guarantees
RSVP requires applications to initiate the request
RSVP by itself does not provide any guarantees
An RSVP-interoperable QoS mechanism (WFQ, CB-WFQ) must be used to implement guarantees
according to RSVP reservations
RSVP is an Internet Engineering Task Force (IETF) signaling protocol, used to
reserve bandwidth in a path between a source and a destination. In RSVP, the
end-node (the application node) station reserves bandwidth for a flow along its path
to a destination in a network. The user can supply the information about how much
capacity to reserve.
RSVP mechanisms enable real-time traffic to reserve bandwidth necessary for
consistent latency. A video conferencing application can use settings in the router
to propagate a request for a path with the required bandwidth and delay for videoconferencing destinations. RSVP then signals all network devices along the path,
and confirms or rejects the reservation. RSVP will check and repeat reservations
at regular intervals. When RSVP is used, the routers sort and prioritize packets
much as a statistical time-division multiplexer would sort and prioritize several
signal sources that share a single channel.
RSVP requires RSVP-aware applications, as signaling is performed by the end-
node. In addition, RSVP does not provide any guarantees by itself. RSVP is the
protocol used to communicate QoS requirements between the end-node and the
layer-3 network, assessing the ability or inability of the network to support the
requested level of service.
RSVP is the signaling protocol underlying the IntServ QoS reference model.
Together with appropriate QoS-enforcing mechanisms in the network, such as
WFQ, it forms a foundation for implementation of IntServ-based services.
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7-4 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-6
End-to-end RSVPEnd-to-end RSVP
All network devices have to be enabled forRSVP
Each network device determines whether ithas enough resources
request request request request
reservereservereservereserve
LocalAdmission
Control
Local
Admission
Control
LocalAdmission
Control
If end-to-end RSVP is desired in a network, all devices in the reservation path
must be RSVP-enabled. When a device receives an RSVP message, it determines
whether it has enough resources to satisfy the reservation request at the local
level.
There are two main RSVP messages used for signaling. When a reservation is
needed, the sending client sends an RSVP PATH message into the network
requesting a specific bandwidth to a specific destination (or multicast address, in
the case of IP multicast application). The purpose of the PATH message is todiscover all RSVP-enabled routers along the path from the sender to the receiver,
and to create initial reservations. The PATH message is forwarded along the flow
path and every intermediate RSVP-capable router adds its identification to the
PATH message. When the receiving end-node receives the PATH message, it
confirms the reservation by replying with an RSVP RESV message. The RESV
message is forwarded back upstream towards the initial sender using the list of
RSVP-enabled routers generated by the PATH message. If the RESV message
successfully arrives at the initial sender, each hop in the end-to-end connection has
reserved the appropriate resources and an end-to-end reservation is established. If
the appropriate resources are not available, the reservation is refused and the
application must default to traditional, best effort communications.RSVP keeps track of the soft state of reservations in routers. This soft state
provides dynamic membership information, adapts to routing changes, and, as the
number of flows increases, enables dynamic changes in reservations to meet those
changing needs. RSVP reservations time out unless periodically refreshed by the
communication endpoint, usually at 30-second intervals.
The benefits of soft state behavior are:
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Copyright 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism 7-5
n Connectionless behavior routers automatically adapt to route changes.
n Timeliness state changes propagate immediately, but only as far as needed.
n Robustness the method is self-correcting, because incorrect reservations
will always time-out even in the most unexpected situations.
n Flexibility provides easy dynamic reservation changes.
The cost of this approach is that it requires ongoing refresh processing for
established states by the endpoints.
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7-6 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-7
Pass-through RSVPPass-through RSVP
Part of the network may not support RSVP
Best-effort delivery is used in those parts
request
request
request
reservereserve
reserve
LocalAdmission
Control
LocalAdmission
Control
Best-effort
forwarding
RSVPnot
enabled
request request
reservereserve
LocalAdmission
Control
When a part of the network does not support RSVP, that is, when the RSVP
messages are not processed by every intermediate hop between the two
application endpoints, some other mechanism may be employed to try to meet the
application requirements in the non-RSVP-enabled part of the network. One such
possibility may be to perform only best-effort delivery between RSVP-enabled
networks using an undersubscribed network in between. The PATH messages
discover all RSVP-aware routers, and are forwarded as plain IP packets on non-
RSVP-enabled hops. The RESV messages are then interpreted only by the RSVP-
aware hops, discovered via the PATH message.
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Copyright 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism 7-7
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-8
Pass-through RSVPwith Class of ServicePass-through RSVPwith Class of Service
Part of the network may not support RSVP
Mark RSVP flows with a Class-of-servicemarker (e.g. IP precedence or DSCP)
Make sure the core provides guarantees tothe RSVP class
request
request
request
reservereserve
reserve
LocalAdmission
Control
LocalAdmission
Control
RSVPnot
enabled
request request
reservereserve
Mark RSVP flowwith DSCP
LocalAdmission
Control
Class-based
guarantee
Another option may be to apply class-of-service based delivery on a non-RSVP-
enabled part of the network. In that case, RSVP-based application traffic is
marked with appropriate class markers (IP precedence or DSCP bits) at the entry
to the non-RSVP-enabled part. The core network can then be engineered to
provide special service to the RSVP class, using, for example, WFQ and WRED.
IP precedence and DSCP are packet markers, located in the ToS byte of the IP
header, which identify traffic classes on each hop in the network. IP precedence
or DSCP bits are usually set at the network edge, where traffic is classified andmarked, and the markers used to identify traffic classes in downstream network
devices. Each device along the path may apply appropriate QoS mechanisms
based on the packet marker, resulting in differentiated per-hop behaviour (PHB)
for each class of traffic. The DiffServ model defines several standard PHBs,
based on marking traffic with the DSCP header bits.
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7-8 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-9
RSVP ApplicationsRSVP Applications
RSVP is used for applications wherebandwidth and delay related guarantees are
necessary
Typical applications are:
Voice over IP (Cisco phones, Microsoft
NetMeeting, ...)
MPLS Traffic Engineering
RSVP allows end systems to request QoS guarantees from the network. The need
for network resource reservations differs for data traffic versus real-time traffic,
as described in the following paragraphs:
n Data traffic seldom needs reserved bandwidth because internetworks provide
datagram services for data traffic. This asynchronous packet switching may
not need guarantees of service quality. End-to-end controls between data
traffic senders and receivers help ensure adequate transmission of bursts of
information.
n Real-time traffic (that is, voice or video information) experiences problems
when using datagram services. Because real-time traffic sends an almost
constant flow of information, the network pipes must be consistent. Some
guarantee must be provided that service between real-time hosts will not vary.
Routers operating on a first-in, first-out (FIFO) basis risk unrecoverable
disruption of the real-time information that is being sent.
Many network-aware applications today use RSVP for signaling. Some well-
known examples include Cisco IP telephones, Microsoft NetMeeting, and MPLS
Traffic Engineering.
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Copyright 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism 7-9
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-10
Configuring Simple RSVPConfiguring Simple RSVP
ip rsvp bandwidth [total-BW[per-flow-BW]]ip rsvp bandwidth [total-BW[per-flow-BW]]
Router(config-if)#
Set the amount of reservable bandwidth (total-BW) and themaximum per-flow reservable bandwidth (per-flow-BW) in kbps
Both default to 75% of the configured bandwidth
Total reservable bandwidth cannot exceed 75% of the
configured bandwidth
bandwidth bandwidthbandwidth bandwidth
Router(config-if)#
Set the interface bandwidth in kbps
This value should reflect the real bandwidth of the link
Basic RSVP is configured by two interface commands. The ip rsvp bandwidthcommand sets the maximum total amount of reservable bandwidth on an interface.
By default, it is configured to 75% of the configured bandwidth, which is also its
maximum allowed value. A per-flow reservable bandwidth can also be configured,
setting the maximum bandwidth a single flow can reserve over this interface. By
default, it is also set to 75% of the configured bandwidth.
Note RSVP cannot be configured with VIP-distributed Cisco Express Forwarding
(dCEF).
The bandwidth interface command sets the interface bandwidth and is used by
routing protocols (to calculate costs) and by a variety of QoS mechanisms. With
RSVP, this is used as the configured bandwidth parameter, referenced by the limits
in the ip rsvp bandwidth command.
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7-10 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-11
Configuring Proxy RSVPConfiguring Proxy RSVP
ip rsvp sender session-IP sender-IP protocol dport sport src-hop-
IP src-intf bandwidth burst
ip rsvp sender session-IP sender-IP protocol dport sport src-hop-
IP src-intf bandwidth burst
Router(config)#
Simulates a host sending a PATH message
Generates a PATH message on behalf of a host or an
application
ip rsvp reservation session-IP sender-IP protocol dport sport
next-hop-IP next-hop-intf{ f f | s e | wf } { r a t e | l oad} bw burst
ip rsvp reservation session-IP sender-IP protocol dport sport
next-hop-IP next-hop-intf{ f f | s e | wf } { r a t e | l oad} bw burst
Router(config)#
Simulates a host sending a RESV message
Generates a RESV message on behalf of a host or an
application
RSVP typically requires both host and network implementations, although Cisco
IOS software provides an RSVP command line interface that allows you to
statically set up RSVP reservations without host involvement.
Use the ip rsvp sender command to make the router simulate that it is receiving
RSVP PATH messages from an upstream host. The command can be used to
proxy RSVP PATH messages for non-RSVP-capable senders. By including a
local (loopback) previous hop address and previous hop interface, you can also use
this command to proxy RSVP for the router you are configuring.
To enable a router to simulate receiving and forwarding Resource Reservation
Protocol (RSVP) RESV messages, use the ip rsvp reservation global
configuration command. To disable this feature, use the no form of this command.
Use this command to make the router simulate receiving RSVP RESV messages
from a downstream host. This command can be used to proxy RSVP RESV
messages for non-RSVP-capable receivers. By giving a local (loopback) next hop
address and next hop interface, you can also use this command to proxy RSVP for
the router you are configuring. Several different reservation types can be specified.
For detailed reservation settings, consult the Cisco IOS documentation.
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Copyright 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism 7-11
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-12
RSVP Admission ControlRSVP Admission Control
RSVP has two tasks:
Determine if there are enough available resources
Determine if the application in question is allowedaccess to these resources
RSVP-enabled devices keep track of existingreservations locally
RSVP-enabled devices can offload theauthorization part of admission control tocentral servers (COPS)
A RSVP-enabled router therefore needs to perform two tasks:
n The router needs to determine whether there are currently available resources,
which can be used to satisfy the reservation request.
n The router needs to be able to authorize an application to make the reservation
request (admission control).
The first task can be performed by keeping track of existing reservations, and of
total reservable capacity locally on each device. If a reservation request exceedsthe locally available reservable resources, the reservation request is denied.
Authorization of reservations could be performed locally, but such an approach
would not scale to more than a few devices. Fortunately, there is a standardized,
centralized framework for policy networking, which includes authorization within
admission control. This framework is based on a set of services and protocols
called the Common Open Policy Service (COPS).
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7-12 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-13
Common Open Policy ServiceCommon Open Policy Service
COPS allows a more centralized approach tobuilding RSVP enabled networks (more scalable)
COPS provides additional control over who canreserve what
request request request request
reservereservereservereserve
LocalAdmission
Control
Remote Admission
Control
LocalAdmission
Control
Policy Decision
Point (PDP)
request
reply
Policy Enforcement
Point (PEP)
Common Open Policy Service (COPS) is an open framework designed for
management in policy networking. COPS provides a service to network devices
and implements management protocols, which enable scalable provisioning of
Quality of Service policies in a network.
COPS is designed so that it provides a centrally managed, but distributed system
for configuring network devices according to centralized policy decisions. In the
case of RSVP, COPS provides centralized databases, which network devices
query for reservation/admission control information. RSVP-enabled devicestherefore need no locally stored configuration, but receive this information in real-
time from the appropriate COPS server. COPS, therefore, scales QoS
provisioning, and enables a device-independent QoS policy throughout the network.
COPS defines the following types of policy services:
n The Policy Enforcement Point (PEP) is the device that enforces network
policy (a router performing RSVP admission control, a firewall filtering traffic).
n The Policy Decision Point (PDP) is the device that stores policy information
and makes it available to the PEP devices.
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Copyright 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism 7-13
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-14
Configuring RSVP for COPSConfiguring RSVP for COPS
Process
Locally?Reject?
Process
Message
Reject Message
Send an error
message to thesource
Yes Yes
No No
Local
Override?
YesDefault
LocalPolicy?
Yes
Process
Remotely?
Ask
PDP
No
No
Reject?
No
Yes
No
YesDefault
Reject?
NoNo
Yes
ip rsvp policy local acl
ip rsvp policy localip rsvp policy local local-override
DefaultRemote
Policy?
The figure shows the flowchart used to consult either the local policy settings, or
the COPS service. Both the local policy and the COPS service can be used
simultaneously on the same router. Individual COPS commands are also presented
in the flowchart, next to the functions they enable.
The admission process in policy networking proceeds as follows for locally
processed messages:
n The router receives a PATH or RESV message and first tries to adjudicate it
locally (that is, without referring to the policy server). If the router has been
configured to adjudicate specific access control lists (ACLs) locally and the
message matches one of those lists, the policy module of the router applies the
operators with which it had been configured. Otherwise, policy processing
continues.
n For each message rejected by the operators, the router sends an error
message to the sender and removes the PATH or RESV message from the
database. If the message is not rejected, policy processing continues.
n If the local override flag is set for this entry, the message is immediately
accepted with the specified policy operators. Otherwise, policy processing
continues.
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7-14 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-15
Configuring RSVP for COPS(cont.)
Configuring RSVP for COPS(cont.)
Process
Locally?Reject?
Process
Message
Reject Message
Send an error
message to thesource
Yes Yes
No No
Local
Override?
YesDefault
LocalPolicy?
Yes
Process
Remotely?
Ask
PDP
No
No
Reject?
No
Yes
No
YesDefault
Reject?
NoNo
Yes
ip rsvp policy cops acl servers
ip rsvp policy default-reject
DefaultRemote
Policy?
ip rsvp policy cops servers
If policy decisions are offloaded to a policy server, policy processing continues as
follows:
n If the message does not match any ACL configured for local policy, the router
applies the default local policy. However, if no default local policy has been
configured, the message is directed toward remote policy processing.
n If the router has been configured with specific ACLs against specific policy
servers (more specifically, PDPs), and the message matches one of these
ACLs, the router sends that message to the specific PDP for adjudication.
Otherwise, policy processing continues.
n If the PDP specifies a reject decision, the message is discarded and an error
message is sent back to the sender, indicating this condition. If the PDP
specifies an accept decision, the message is accepted and processed using
normal RSVP processing rules.
n If the message does not match any ACL configured for specific PDPs, the
router applies the default PDP configuration. If a default COPS configuration
has been entered, policy processing continues. Otherwise, the message is
considered to be unmatched.
n If the default policy decision for unmatched messages is to reject, the message
is immediately discarded and an ERROR message is sent to the sender
indicating this condition. Otherwise, the message is accepted and processed
using normal RSVP processing rules.
Whenever a request for adjudication (of any sort) is sent to a PDP, a 30-second
timer associated with the PATH or RESV message is started. If the timer runs out
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Copyright 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism 7-15
before the PDP replies to the request, the PDP is assumed to be down and the
request is given to the default policy.
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7-16 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-15
RSVPExample
RSVPExample
interface Serial0/0
bandwidth 256
ip address 10.5.8.65 255.255.255.252encapsulation ppp
fair-queue 64 256 20ip rtp header-compression
ip rsvp bandwidth 160
interface Serial0/0
bandwidth 128ip address 10.10.3.33 255.255.255.252
encapsulation ppp
fair-queue 64 256 10ip rtp header-compression
ip rsvp bandwidth 80
The figure shows a basic example of RSVP configuration in Cisco IOS routers.
The two routers in the figure are both configured for RSVP, and both utilize WFQ
to guarantee bandwidth to RSVP flows in RSVP-reserved queues. Different
maximum reservable bandwidths are allocated, based on the real bandwidth of the
link.
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Copyright 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism 7-17
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-16
RSVP with COPSExample
RSVP with COPSExample
interface Serial0/0bandwidth 2048
ip address 10.1.1.1 255.255.255.252encapsulation ppp
fair-queue 64 256 100
ip rsvp bandwidth 512!
ip rsvp policy cops 100 servers 10.100.1.1 10.101.1.1ip rsvp policy default-reject
ip rsvp policy cops minimal
ip rsvp policy cops timeout 600ip rsvp policy cops report-all
!access-list 100 permit udp any any
COPS(PEP)
COPS(PDP)
This figure shows a COPS-enabled RSVP configuration. The RSVP interface
configuration does not change, and COPS parameters are defined with the ip rsvp
policy commands. In this example, the COPS PDP adjudicates all UDP traffic
reservations.
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7-18 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-17
Monitoring and TroubleshootingRSVP
Monitoring and TroubleshootingRSVP
show ip rsvp installed [detail]show ip rsvp installed [detail]
Router#
Lists installed reservations per interface
Router#show ip rsvp installed
RSVP:Ethernet2/1
BPS To From Protoc DPort Sport Weight
Conversation
44K 145.20.0.202 145.10.0.201 UDP 1000 1000 0 264
44K 145.20.0.202 145.10.0.201 UDP 1001 1001 13 266
98K 145.20.0.202 145.10.0.201 UDP 1002 1002 6 265
1K 145.20.0.202 145.10.0.201 UDP 10 10 0 264
RSVP:Serial3/0 has no installed reservations
Router#show ip rsvp installed
RSVP:Ethernet2/1
BPS To From Protoc DPort Sport Weight
Conversation
44K 145.20.0.202 145.10.0.201 UDP 1000 1000 0 264
44K 145.20.0.202 145.10.0.201 UDP 1001 1001 13 266
98K 145.20.0.202 145.10.0.201 UDP 1002 1002 6 265
1K 145.20.0.202 145.10.0.201 UDP 10 10 0 264
RSVP:Serial3/0 has no installed reservations
The show ip rsvp installed command shows all active conversations over an
RSVP-enabled path, which has resource reservations installed. The actual
reserved bandwidth is shown, along with the session parameters (endpoints and
applications).
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Copyright 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism 7-19
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-18
Monitoring and TroubleshootingRSVP
Monitoring and TroubleshootingRSVP
show ip rsvp installed [detail] [interface]show ip rsvp installed [detail] [interface]
Router#
Router#show ip rsvp installed detail
RSVP:Ethernet2/1 has the following installed reservationsRSVP Reservation. Destination is 145.20.0.202, Source is 145.10.0.201,
Protocol is UDP, Destination port is 1000, Source port is 1000Reserved bandwidth:44K bits/sec, Maximum burst:1K bytes, Peak rate: 44K bits/sec
QoS provider for this flow:WFQ. Conversation number:264. Weight:0 (PQ)
Conversation supports 1 reservationsData given reserved service:316 packets (15800 bytes)
Data given best-effort service:0 packets (0 bytes)Reserved traffic classified for 104 seconds
Long-term average bitrate (bits/sec):1212 reserved, 0M best-effort
RSVP Reservation. Destination is 145.20.0.202, Source is 145.10.0.201,Protocol is UDP, Destination port is 1001, Source port is 1001
Reserved bandwidth:44K bits/sec, Maximum burst:3K bytes, Peak rate: 44K bits/secQoS provider for this flow:WFQ. Conversation number:266. Weight:13
Conversation supports 1 reservationsData given reserved service:9 packets (450 bytes)
Data given best-effort service:0 packets (0 bytes)
Reserved traffic classified for 107 secondsLong-term average bitrate (bits/sec):33 reserved, 0M best-effort
...
Router#show ip rsvp installed detailRSVP:Ethernet2/1 has the following installed reservations
RSVP Reservation. Destination is 145.20.0.202, Source is 145.10.0.201,
Protocol is UDP, Destination port is 1000, Source port is 1000Reserved bandwidth:44K bits/sec, Maximum burst:1K bytes, Peak rate: 44K bits/sec
QoS provider for this flow:WFQ. Conversation number:264. Weight:0 (PQ)Conversation supports 1 reservations
Data given reserved service:316 packets (15800 bytes)Data given best-effort service:0 packets (0 bytes)
Reserved traffic classified for 104 seconds
Long-term average bitrate (bits/sec):1212 reserved, 0M best-effortRSVP Reservation. Destination is 145.20.0.202, Source is 145.10.0.201,
Protocol is UDP, Destination port is 1001, Source port is 1001Reserved bandwidth:44K bits/sec, Maximum burst:3K bytes, Peak rate: 44K bits/sec
QoS provider for this flow:WFQ. Conversation number:266. Weight:13
Conversation supports 1 reservationsData given reserved service:9 packets (450 bytes)
Data given best-effort service:0 packets (0 bytes)Reserved traffic classified for 107 seconds
Long-term average bitrate (bits/sec):33 reserved, 0M best-effort...
The show ip rsvp installed detail command shows detailed information about
active conversations currently installed in the RSVP reservation table. Detailed
timing and accounting for every conversation is displayed, together with the QoS
mechanism used to provide service guarantees.
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7-20 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-19
Monitoring and TroubleshootingRSVP
Monitoring and TroubleshootingRSVP
show ip rsvp reservation [detail]show ip rsvp reservation [detail]
Router(config)#
List RSVP reservations
show ip rsvp request [detail]show ip rsvp request [detail]
Router(config)#
List pending RSVP requests
The show ip rsvp reservation command lists all existing RSVP reservations over
an interface. The show ip rsvp request command shows all pending RSVP
requests that have no fixed reservation in place.
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Copyright 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism 7-21
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-20
Monitoring and TroubleshootingRSVP with COPS
Monitoring and TroubleshootingRSVP with COPS
show ip rsvp policy [{cops | local} [acl]]show ip rsvp policy [{cops | local} [acl]]
Router#
Router#show ip rsvp policy cops
COPS/RSVP settings:Generate reports for all decisions
Do not query PDP for error messages
COPS/RSVP entry. ACLs: 100PDPs: 10.100.1.1 10.101.1.1
Current state: ConnectedCurrently connected to PDP 10.100.1.1, port 0
COPS/RSVP entry. ACLs: 101PDPs: 10.102.1.1
Current state: In reconnect loop waitReconnect timer is 960 seconds
Router#show ip rsvp policy cops
COPS/RSVP settings:Generate reports for all decisions
Do not query PDP for error messagesCOPS/RSVP entry. ACLs: 100
PDPs: 10.100.1.1 10.101.1.1Current state: Connected
Currently connected to PDP 10.100.1.1, port 0
COPS/RSVP entry. ACLs: 101
PDPs: 10.102.1.1Current state: In reconnect loop wait
Reconnect timer is 960 seconds
Lists all policies
The show ip rsvp policy command shows the policy settings, whether the policy
is locally defined or policy decisions are offloaded to the COPS server. The output
shows associations between flow specifications and associated COPS servers,
which perform admission control for those flows. This command is used to verify
connectivity to COPS services and the associations between the local device and a
COPS server.
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7-22 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-21
Monitoring and TroubleshootingRSVP with COPS
Monitoring and TroubleshootingRSVP with COPS
show cops serversshow cops servers
Router#
Router#show cops serversCOPS SERVER: Address: 10.100.1.1. Port: 3288. State: 0. Keepalive: 120 sec
Number of clients: 1. Number of sessions: 1.
COPS CLIENT: Client type: 1. State: 0.
Router#show cops serversCOPS SERVER: Address: 10.100.1.1. Port: 3288. State: 0. Keepalive: 120 sec
Number of clients: 1. Number of sessions: 1.
COPS CLIENT: Client type: 1. State: 0.
Lists all COPS servers
The show cops servers command displays the state of all configured COPS
servers.
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Copyright 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism 7-23
Summary
n RSVP enables end-stations to signal QoS requirements to the network.
n RSVP does not provide any guarantees; router QoS mechanisms do.
n RSVP does not necessarily require an end-to-end RSVP-aware path.
n COPS provides scalable QoS provisioning.
Lesson Review
1. What is RSVP used for?
2. Does RSVP provide QoS guarantees?
3. What QoS mechanism should be used to provide QoS guarantees to RSVP
reservations?
4. What are the benefits of using COPS with RSVP?
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7-24 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
Subnet Bandwidth Management
Overview
This section describes a mechanism that is used on shared media where more
complex reservation is required. SBM protocol is used between RSVP devices
reachable over the same subnet.
Objectives
Upon completion of this lesson, you will be able to perform the following tasks:
n Describe Subnet Bandwidth Management (SBM).
n Configure SBM.
n Monitor and troubleshoot RSVP with SBM.
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Subnet Bandwidth ManagementSubnet Bandwidth Management
RSVP manages unidirectional reservation ofresources
RSVP on shared media can result inoversubscription
SBM is an add-on to RSVP on shared mediato prevent oversubscription
RSVP is used to manage reservation of resources unidirectionally, between Layer-
3 hops. On a shared medium, many Layer-3 hops can be active between many
routers on the shared segment. The shared medium is shared between all routers,
therefore the routers need to keep track about all routers usage of the shared
medium, in order to maintain a consistent picture of available bandwidth on that
medium. If routers were independently reserving bandwidth over a shared medium,
oversubscription would occur if each router had full access to the medium
bandwidth.
Subnet Bandwidth Management (SBM) is an add-on to the RSVP protocol, which
provides arbitration of bandwidth allocation on a shared medium to prevent RSVP-
caused oversubscription. SBM specifies a signaling 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 signaling method is similar to that of RSVP itself.
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7-26 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-27
Without SBMWithout SBM
Both routers are within the 75% reservable limit
Total reserved bandwidth is 13 Mbps (above Ethernet bandwidth)
Ethernet should be treated carefully because it is impossible toachieve 100% utilization (collisions; depending on implementation)
Ethernet
Ethernet bandwidth 10Mbps
7.5 Mbps is reservable
Reserve6
Mbps
Reserve7Mbps
Reserve 6 Mbps
Reserve 7 Mbps
0 Mbps booked7.5 Mbps free
0 Mbps booked7.5 Mbps free
6 Mbps booked1.5 Mbps free
7 Mbps booked512 kbps free
The figure shows a possible scenario of RSVP oversubscription on a shared
segment. Both right-hand routers think of the Ethernet segment as a link with a
bandwidth of 10 Mbps. Based on the 75% rule, by default 7.5 Mbps of that
bandwidth is reservable. The upper router reserves 6 Mbps of the reservable
bandwidth, and the bottom router reserves 7 Mbps of the reservable bandwidth.
Obviously, the combined reserved bandwidth exceeds the Ethernet media
bandwidth and results in an unwanted oversubscription.
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With SBMWith SBM
Reserve 6 Mbps
Reserve 7 Mbps
0 Mbps booked7.5 Mbps free
0 Mbps booked7.5 Mbps free
6 Mbps booked1.5 Mbps free
7 Mbps booked512 kbps free
Reserve 6 Mbps Reserve6M
bps
Reserve6Mbps
One of the routers on thesegment is elected to be the
Designated SubnetBandwidth Manager (DSBM)
The shared media is
effectively transformed into astar of point-to-point links
Error
0 Mbps booked7.5 Mbps free
6 Mbps booked1.5 Mbps free
SBMs solution to the problem is to introduce a Designated Subnet Bandwidth
Manager (DSBM) router, which tracks all reservations over a shared segment.
The DSBM is one of the existing subnet routers, designated to be the DSBM via
an election process on the subnet. When a DSBM is used, the shared medium is
effectively transformed into a virtual mesh of point-to-point links.
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
segments DSBM instead of to the RSVP session destination address, as is done inconventional 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.
n The DSBM receives the RSVP reservation request (RSVP RESV) message
and processes it in a manner similar to the way RSVP itself handles
reservation request processing, basing the outcome on available bandwidth.
The procedure is as follows:
n If it cannot grant the request because of lack of resources, the DSBM returns
a RESVERR message to the requester.n If sufficient resources are available and the DSBM can grant the reservation
request, it forwards the RESV message toward the PHOP(s) using the local
PATH state for the session.
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7-28 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
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DSBM ElectionDSBM Election
DSBM is elected based on the DSBM priority
Each DSBM candidate advertises its priorityin the range from 64 to 128
The candidate with the highest priority iselected to be the DSBM
RSVP enabled devices can participate inSubnet Bandwidth Management withoutbeing DSBM candidates
On a LAN segment configured for SBM, a DSBM is elected based on each
routers DSBM-candidate priority. All RSVP messages of participating routers are
sent to the DSBM to adjudicate the reservation requests. Such a LAN segment is
called a managed segment in SBM terms.
Of all SBM-enabled routers on a segment, some or all routers are DSBM
candidates; that is, not all routers need to be configured as DSBM candidates to
perform SBM-assisted RSVP. A DSBM is chosen among the candidates based on
the configured DSBM priority, which ranges from 64 to 128, the latter being thehighest priority.
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Configuring DSBMConfiguring DSBM
ip rsvp dsbm candidatepriorityip rsvp dsbm candidatepriority
Router(config-if)#
Configures the router to bid in the election of the DSBM Default priority is 64
ip rsvp dsbm non-resv-send-limit {burst | max-unit | min-
unit | peak | rate} value
ip rsvp dsbm non-resv-send-limit {burst | max-unit | min-
unit | peak | rate} value
Router(config)#
The NonResvSendLimit object specifies how much traffic can be
sent onto a managed segment without a valid RSVP reservation
All values are unlimited by default
The ip rsvp dsbm candidate interface command specifies this router as a
DSBM candidate on the attached LAN network. A priority used in the DSBM
election process is assigned, the default being the lowest priority of 64.
The ip rsvp dsbm non-resv-send-limit command limits the amount of traffic,
which can be sent to a managed segment without an RSVP reservation. By
default, any amount of traffic can be sent to the segment. This command should be
used in a network, where RSVP is predominantly used for signaling to allow some
non-RSVP traffic to transit shared LAN segments.
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SBMExample
SBMExample
interface Ethernet0/0
ip address 10.1.1.1 255.255.255.0ip rsvp bandwidth 7500 7500
ip rsvp dsbm candidate 100
ip rsvp dsbm non-resv-send-limit rate 100
ip rsvp dsbm non-resv-send-limit burst 1000
ip rsvp dsbm non-resv-send-limit peak 100
!
interface Ethernet0/0
ip address 10.1.1.1 255.255.255.0ip rsvp bandwidth 7500 7500
ip rsvp dsbm candidate 100
ip rsvp dsbm non-resv-send-limit rate 100
ip rsvp dsbm non-resv-send-limit burst 1000
ip rsvp dsbm non-resv-send-limit peak 100
!
The figure shows an interface configuration example, where SBM is used to signal
RSVP across a shared LAN segment. The local router is configured as a DSBM
candidate, and RSVP with SBM is enabled using the ip rsvp bandwidth
command. In this example, non-reserved traffic is limited to a mere 100 Kbps, with
one-megabyte bursts allowed. Such an example configuration could be used in a
fully RSVP-enabled network, where some bandwidth needs to be provisioned for
network control (routing protocols, time management, and so forth).
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Monitoring and TroubleshootingSBM
Monitoring and TroubleshootingSBM
show ip sbm [detail]show ip sbm [detail]
Router#
Lists interfaces where SBM is active The detailed option displays detailed information about local
configuration and the DSBM configuration
Router#show ip rsvp sbm
Interface DSBM Addr DSBM Priority DSBM Candidate My PriorityEt0/0 10.1.1.1 100 yes 100
Et0/1 10.1.2.1 100 yes 100Router#show ip rsvp sbm detail
Interface:Ethernet0/0
Local Configuration Current DSBMIP Address:10.1.1.1 IP Address:10.1.1.1
DSBM candidate:yes I Am DSBM:yesPriority:100 Priority:100
Non Resv Send Limit Non Resv Send LimitRate:100 Kbytes/sec Rate:100 Kbytes/sec
Burst:1000 Kbytes Burst:1000 Kbytes
Peak:100 Kbytes/sec Peak:100 Kbytes/secMin Unit:unlimited Min Unit:unlimited
Max Unit:unlimited Max Unit:unlimited
Router#show ip rsvp sbmInterface DSBM Addr DSBM Priority DSBM Candidate My Priority
Et0/0 10.1.1.1 100 yes 100Et0/1 10.1.2.1 100 yes 100
Router#show ip rsvp sbm detail
Interface:Ethernet0/0Local Configuration Current DSBM
IP Address:10.1.1.1 IP Address:10.1.1.1DSBM candidate:yes I Am DSBM:yes
Priority:100 Priority:100
Non Resv Send Limit Non Resv Send LimitRate:100 Kbytes/sec Rate:100 Kbytes/sec
Burst:1000 Kbytes Burst:1000 KbytesPeak:100 Kbytes/sec Peak:100 Kbytes/sec
Min Unit:unlimited Min Unit:unlimitedMax Unit:unlimited Max Unit:unlimited
The show ip sbm command shows per-interface SBM parameters, displaying
other SBM-enabled routers on the attached segment. The show ip sbm detail
command also shows the non-reserved sending limits of discovered neighbors.
In this output, all routers on the segment have the same DSBM priority. In that
case, the tiebreaker is a routers IP address on that segment, and the router with
the highest IP address will win the election.
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7-32 IP QoS Signaling Mechanism Copyright 2001, Cisco Systems, Inc.
Summary
n SBM enables RSVP to run over shared LAN segments.
n DSBM routers provide shared LAN adjudication of RSVP-reservations.
n SBM can limit the amount of non-RSVP traffic sent into a network.
Lesson Review
1. What is the purpose of Subnet Bandwidth Management?
2. How do routers on a common subnet communicate reservation requests?
3. What is a DSBM?
4. How do routers elect a DSBM?
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Summary
n RSVP enables end-stations to signal QoS requirements to the network
n RSVP does not provide any guarantees; router QoS mechanisms do.
n SBM enables RSVP to run over shared LAN segments.
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Review Questions and Answers
Resource Reservation Protocol (RSVP)
Question: What is RSVP used for?
Answer: RSVP is used by applications to signal their QoS requirements to the
network and to set up reservations along the application path.Question: Does RSVP provide QoS guarantees?
Answer: No, RSVP is only used for signaling. Per-hop mechanisms, such as
WFQ, are used to guarantee a service level to a RSVP-enabled application.
Question: What QoS mechanism should be used to provide QoS guarantees to
RSVP reservations?
Answer: Usually, WFQ and CB-WFQ are used to provide per-hop guarantees.
Question: What are the benefits of using COPS with RSVP?
Answer: Using COPS-compliant policy management software enables scaling of
RSVP-enabled networks by offloading part of the admission control functions to
a centralized database.
Subnet Bandwidth Management
Question: What is the purpose of Subnet Bandwidth Management?
Answer: The purpose of SBM is to prevent oversubscription of a shared segment
by introducing an arbiter, which keeps tracks of all reservations over a shared
segment.
Question: How do routers on a common subnet communicate reservationrequests?
Answer: Routers communicate reservation requests by forwarding all RSVP
messages to the arbiter (the DSBM).
Question: What is a DSBM?
Answer: The DSBM (Designated Subnet Bandwidth Manager) is an elected layer-
3 device on a shared segment, which keeps tracks of all reservations.
Question: How do routers elect a DSBM?
Answer: Routers elect a DSBM with a priority-based election system. Router IP
address is the final tiebreaker.
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