s07 - ip qos - signaling mechnisms

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. 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. Copyright  2001, Cisco Systems, Inc. IP QoS Signaling Mechanism 7-3 © 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-5 Resource Reservation Protocol Resource Reservation Protocol • RSVP is a protocol used to reserve resources in a path between a source and a destination • RSVP signals all network devices that a certain application 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 video conferencing 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. 7-4 IP QoS Signaling Mechanism Copyright  2001, Cisco Systems, Inc. © 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-6 End-to-end RSVP End-to-end RSVP • All network devices have to be enabled for RSVP • Each network device determines whether it has enough resources request request request request reservereservereservereserve Local Admission Control Local Admission Control Local Admission 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 to discover 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: 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. 7-6 IP QoS Signaling Mechanism Copyright  2001, Cisco Systems, Inc. © 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-7 Pass-through RSVP Pass-through RSVP • Part of the network may not support RSVP • Best-effort delivery is used in those parts request request request reserve reserve reserve Local Admission Control Local Admission Control Best-effort forwarding RSVP not enabled request request reservereserve Local Admission 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. Copyright  2001, Cisco Systems, Inc. IP QoS Signaling Mechanism 7-7 © 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-8 Pass-through RSVP with Class of Service Pass-through RSVP with Class of Service • Part of the network may not support RSVP • Mark RSVP flows with a Class-of-service marker (e.g. IP precedence or DSCP) • Make sure the core provides guarantees to the RSVP class request request request reserve reserve reserve Local Admission Control Local Admission Control RSVP not enabled request request reservereserve Mark RSVP flow with DSCP Local Admission 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 and marked, 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. 7-8 IP QoS Signaling Mechanism Copyright  2001, Cisco Systems, Inc. © 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-9 RSVP Applications RSVP Applications • RSVP is used for applications where bandwidth 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. Copyright  2001, Cisco Systems, Inc. IP QoS Signaling Mechanism 7-9 © 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-10 Configuring Simple RSVP Configuring 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 the maximum 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 bandwidth bandwidth 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 bandwidth command 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. 7-10 IP QoS Signaling Mechanism Copyright  2001, Cisco Systems, Inc. © 2001, Cisco Systems, Inc. IP QoS Signaling Mechanism-11 Configuring Proxy RSVP Configuring 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 {ff | se | wf} {rate | load} bw burst ip rsvp reservation session-IP sender-IP protocol dport sport next-hop-IP next-hop-intf {ff | se | wf} {rate | load} 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. [...]... bandwidth 7500 7500 ip rsvp dsbm candidate 100 ip rsvp dsbm ip rsvp dsbm non-resv-send-limit rate 100 ip rsvp dsbm ip rsvp dsbm non-resv-send-limit burst 1000 ip rsvp dsbm non-resv-send-limit burst 1000 ip rsvp dsbm non-resv-send-limit peak 100 ip rsvp dsbm ! ! © 2001, Cisco Systems, Inc IP QoS Signaling Mechanism -3 1 The figure shows an interface configuration example, where SBM is used to signal RSVP across... used for signaling to allow some non-RSVP traffic to transit shared LAN segments Copyright © 2001, Cisco Systems, Inc IP QoS Signaling Mechanism 7-2 9 SBM Example interface Ethernet0/0 interface Ethernet0/0 ip address 10.1.1.1 255.255.255.0 ip address 10.1.1.1 255.255.255.0 ip rsvp bandwidth 7500 7500 ip rsvp bandwidth 7500 7500 ip rsvp dsbm candidate 100 ip rsvp dsbm ip rsvp dsbm non-resv-send-limit... 0 State: 0 IP QoS Signaling Mechanism -2 1 The show cops servers command displays the state of all configured COPS servers 7-2 2 IP QoS Signaling Mechanism Copyright © 2001, Cisco Systems, Inc 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... 10.100.1.1 10.101.1.1 ip rsvp policy default-reject ip rsvp policy cops minimal ip rsvp policy cops timeout 600 ip rsvp policy cops report-all ! access-list 100 permit udp any any © 2001, Cisco Systems, Inc IP QoS Signaling Mechanism -1 6 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... 128 ip address 10.10.3.33 255.255.255.252 encapsulation ppp fair-queue 64 256 10 ip rtp header-compression ip rsvp bandwidth 80 interface Serial0/0 bandwidth 256 ip address 10.5.8.65 255.255.255.252 encapsulation ppp fair-queue 64 256 20 ip rtp header-compression ip rsvp bandwidth 160 © 2001, Cisco Systems, Inc IP QoS Signaling Mechanism -1 5 The figure shows a basic example of RSVP configuration in Cisco... together with the QoS mechanism used to provide service guarantees Copyright © 2001, Cisco Systems, Inc IP QoS Signaling Mechanism 7-1 9 Monitoring and Troubleshooting RSVP Router(config)# show ip rsvp reservation [detail] • List RSVP reservations Router(config)# show ip rsvp request [detail] • List pending RSVP requests © 2001, Cisco Systems, Inc IP QoS Signaling Mechanism -1 9 The show ip rsvp reservation... 264 264 IP QoS Signaling Mechanism -1 7 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) 7-1 8 IP QoS Signaling Mechanism Copyright © 2001, Cisco Systems, Inc Monitoring and Troubleshooting RSVP Router# show ip rsvp... ranges from 64 to 128, the latter being the highest priority 7-2 8 IP QoS Signaling Mechanism Copyright © 2001, Cisco Systems, Inc Configuring DSBM Router(config-if)# ip rsvp dsbm candidate priority • Configures the router to bid in the election of the DSBM • Default priority is 64 Router(config)# ip rsvp dsbm non-resv-send-limit {burst | max-unit | minrsvp dsbm unit | peak | rate} value • The NonResvSendLimit... DSBM? 4 How do routers elect a DSBM? 7-3 2 IP QoS Signaling Mechanism Copyright © 2001, Cisco Systems, Inc 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 Copyright © 2001, Cisco Systems, Inc IP QoS Signaling Mechanism 7-3 3 Review Questions and Answers Resource... PDP, a 30-second timer associated with the PATH or RESV message is started If the timer runs out 7-1 4 IP QoS Signaling Mechanism Copyright © 2001, Cisco Systems, Inc before the PDP replies to the request, the PDP is assumed to be down and the request is given to the default policy Copyright © 2001, Cisco Systems, Inc IP QoS Signaling Mechanism 7-1 5 RSVP Example interface Serial0/0 bandwidth 128 ip address . RSVP Configuring 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. application ip rsvp reservation session -IP sender -IP protocol dport sport next-hop -IP next-hop-intf {ff | se | wf} {rate | load} bw burst ip rsvp reservation session -IP sender -IP protocol dport. QoS Signaling Mechanism-10 Configuring Simple RSVP Configuring Simple RSVP ip rsvp bandwidth [total-BW [per-flow-BW]] ip rsvp bandwidth [total-BW [per-flow-BW]] Router(config-if)# • Set the amount