This module describes how to implement Resource Reservation Protocol (RSVP) for MPLS Traffic Engineering (MPLS-TE) on Cisco ASR 9000 Series Aggregation Services Routers.
The Multiprotocol Label Switching (MPLS) is a standards-based solution, driven by the Internet Engineering Task Force (IETF), devised to convert the Internet and IP backbones from best-effort networks into business-class transport media.
Resource Reservation Protocol (RSVP) is a signaling protocol that enables systems to request resource reservations from the network. RSVP processes protocol messages from other systems, processes resource requests from local clients, and generates protocol messages. As a result, resources are reserved for data flows on behalf of local and remote clients. RSVP creates, maintains, and deletes these resource reservations.
RSVP provides a secure method to control quality-of-service (QoS) access to a network.
MPLS Traffic Engineering (MPLS-TE) uses RSVP to signal label switched paths (LSPs).
These prerequisites are required to implement RSVP for MPLS-TE :
You must be in a user group associated with a task group that includes the proper task IDs. The command reference guides include the task IDs required for each command. If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance.
Either a composite mini-image plus an MPLS package, or a full image, must be installed.
Information About Implementing RSVP for MPLS-TE
To implement MPLS RSVP, you must understand the these concepts:
RSVP is a network control protocol that enables Internet applications to signal LSPs for MPLS-TE . The RSVP implementation is compliant with the IETF RFC 2205, andRFC 3209.
RSVP is automatically enabled on interfaces on which MPLS-TE is configured. For MPLS-TE LSPs with nonzero bandwidth, the RSVP bandwidth has to be configured on the interfaces. There is no need to configure RSVP, if all MPLS-TE LSPs have zero bandwidth.
RSVP Refresh Reduction, defined in RFC 2961, includes support for reliable messages and summary refresh messages. Reliable messages are retransmitted rapidly if the message is lost. Because each summary refresh message contains information to refresh multiple states, this greatly reduces the amount of messaging needed to refresh states. For refresh reduction to be used between two routers, it must be enabled on both routers. Refresh Reduction is enabled by default.
Message rate limiting for RSVP allows you to set a maximum threshold on the rate at which RSVP messages are sent on an interface. Message rate limiting is disabled by default.
The process that implements RSVP is restartable. A software upgrade, process placement or process failure of RSVP or any of its collaborators, has been designed to ensure Nonstop Forwarding (NSF) of the data plane.
RSVP supports graceful restart, which is compliant with RFC 3473. It follows the procedures that apply when the node reestablishes communication with the neighbor’s control plane within a configured restart time.
It is important to note that RSVP is not a routing protocol. RSVP works in conjunction with routing protocols and installs the equivalent of dynamic access lists along the routes that routing protocols calculate. Because of this, implementing RSVP in an existing network does not require migration to a new routing protocol.
LSP setup is initiated when the LSP head node sends path messages to the tail node (see the RSVP Operation figure ).
Figure 1. RSVP Operation
The Path messages reserve resources along the path to each node, creating Path soft states on each node. When the tail node receives a path message, it sends a reservation (RESV) message with a label back to the previous node. When the reservation message arrives at the previous node, it causes the reserved resources to be locked and forwarding entries are programmed with the MPLS label sent from the tail-end node. A new MPLS label is allocated and sent to the next node upstream.
When the reservation message reaches the head node, the label is programmed and the MPLS data starts to flow along the path.
RSVP is designed to ensure nonstop forwarding under the following constraints:
Ability to tolerate the failure of one RP of a 1:1 redundant pair.
Hitless software upgrade.
The RSVP high availability (HA) design follows the constraints of the underlying architecture where processes can fail without affecting the operation of other processes. A process failure of RSVP or any of its collaborators does not cause any traffic loss or cause established LSPs to go down. When RSVP restarts, it recovers its signaling states from its neighbors. No special configuration or manual intervention are required. You may configure RSVP graceful restart, which offers a standard mechanism to recover RSVP state information from neighbors after a failure.
RSVP graceful restart provides a control plane mechanism to ensure high availability (HA), which allows detection and recovery from failure conditions while preserving nonstop forwarding services on the systems running Cisco IOS XR software.
RSVP graceful restart provides a mechanism that minimizes the negative effects on MPLS traffic caused by these types of faults:
Disruption of communication channels between two nodes when the communication channels are separate from the data channels. This is called control channel failure.
Control plane of a node fails but the node preserves its data forwarding states. This is called node failure.
The procedure for RSVP graceful restart is described in the “Fault Handling” section of RFC 3473, Generalized MPLS Signaling, RSVP-TE Extensions. One of the main advantages of using RSVP graceful restart is recovery of the control plane while preserving nonstop forwarding and existing labels.
When you configure RSVP graceful restart, Cisco IOS XR software sends and expects node-id address based Hello messages (that is, Hello Request and Hello Ack messages). The RSVP graceful restart Hello session is not established if the neighbor router does not respond with a node-id based Hello Ack message.
You can also configure graceful restart to respond (send Hello Ack messages) to interface-address based Hello messages sent from a neighbor router in order to establish a graceful restart Hello session on the neighbor router. If the neighbor router does not respond with node-id based Hello Ack message, however, the RSVP graceful restart Hello session is not established.
Cisco IOS XR software provides two commands to configure graceful restart:
signalling hello graceful-restart
signalling hello graceful-restart interface-based
By default, graceful restart is disabled. To enable interface-based graceful restart, you must first enable standard graceful restart. You cannot enable interface-based graceful restart independently.
Figure 2. Node Failure with RSVP.
This figure illustrates how RSVP graceful restart handles a node failure condition.
RSVP graceful restart requires the use of RSVP hello messages. Hello messages are used between RSVP neighbors. Each neighbor can autonomously issue a hello message containing a hello request object. A receiver that supports the hello extension replies with a hello message containing a hello acknowledgment (ACK) object. This means that a hello message contains either a hello Request or a hello ACK object. These two objects have the same format.
The restart cap object indicates a node’s restart capabilities. It is carried in hello messages if the sending node supports state recovery. The restart cap object has the following two fields:
Time after a loss in Hello messages within which RSVP hello session can be reestablished. It is possible for a user to manually configure the Restart Time.
Time that the sender waits for the recipient to re-synchronize states after the re-establishment of hello messages. This value is computed and advertised based on number of states that existed before the fault occurred.
For graceful restart, the hello messages are sent with an IP Time to Live (TTL) of 64. This is because the destination of the hello messages can be multiple hops away. If graceful restart is enabled, hello messages (containing the restart cap object) are send to an RSVP neighbor when RSVP states are shared with that neighbor.
Restart cap objects are sent to an RSVP neighbor when RSVP states are shared with that neighbor. If the neighbor replies with hello messages containing the restart cap object, the neighbor is considered to be graceful restart capable. If the neighbor does not reply with hello messages or replies with hello messages that do not contain the restart cap object, RSVP backs off sending hellos to that neighbor. If graceful restart is disabled, no hello messages (Requests or ACKs) are sent. If a hello Request message is received from an unknown neighbor, no hello ACK is sent back.
ACL-based Prefix Filtering
RSVP provides for the configuration of extended access lists (ACLs) to forward, drop, or perform normal processing on RSVP router-alert (RA) packets. Prefix filtering is designed for use at core access routers in order that RA packets (identified by a source/destination address) can be seamlessly forwarded across the core from one access point to another (or, conversely to be dropped at this node). RSVP applies prefix filtering rules only to RA packets because RA packets contain source and destination addresses of the RSVP flow.
RA packets forwarded due to prefix filtering must not be sent as RSVP bundle messages, because bundle messages are hop-by-hop and do not contain RA. Forwarding a Bundle message does not work, because the node receiving the messages is expected to apply prefix filtering rules only to RA packets.
For each incoming RSVP RA packet, RSVP inspects the IP header and attempts to match the source/destination IP addresses with a prefix configured in an extended ACL. The results are as follows:
If an ACL does not exist, the packet is processed like a normal RSVP packet.
If the ACL match yields an explicit permit (and if the packet is not locally destined), the packet is forwarded. The IP TTL is decremented on all forwarded packets.
If the ACL match yields an explicit deny, the packet is dropped.
If there is no explicit permit or explicit deny, the ACL infrastructure returns an implicit (default) deny. RSVP can be configured to drop the packet. By default, RSVP processes the packet if the ACL match yields an implicit (default) deny.
Information About Implementing RSVP Authentication
Before implementing RSVP authentication, you must configure a keychain first. The name of the keychain must be the same as the one used in the keychain configuration. For more information about configuring keychains, see Cisco ASR 9000 Series Aggregation Services Router System Security Configuration Guide .
RSVP authentication supports only keyed-hash message authentication code (HMAC) type algorithms.
To implement RSVP authentication on Cisco IOS XR software, you must understand the following concepts:
You can carry out these tasks with RSVP authentication:
Set up a secure relationship with a neighbor by using secret keys that are known only to you and the neighbor.
Configure RSVP authentication in global, interface, or neighbor configuration modes.
Authenticate incoming messages by checking if there is a valid security relationship that is associated based on key identifier, incoming interface, sender address, and destination address.
Add an integrity object with message digest to the outgoing message.
Use sequence numbers in an integrity object to detect replay attacks.
RSVP Authentication Design
Network administrators need the ability to establish a security domain to control the set of systems that initiates RSVP requests.
The RSVP authentication feature permits neighbors in an RSVP network to use a secure hash to sign all RSVP signaling messages digitally, thus allowing the receiver of an RSVP message to verify the sender of the message without relying solely on the sender's IP address.
The signature is accomplished on a per-RSVP-hop basis with an RSVP integrity object in the RSVP message as defined in RFC 2747. This method provides protection against forgery or message modification. However, the receiver must know the security key used by the sender to validate the digital signature in the received RSVP message.
Network administrators manually configure a common key for each RSVP neighbor on the shared network.
The following reasons explain how to choose between global, interface, or neighbor configuration modes:
Global configuration mode is optimal when a router belongs to a single security domain (for example, part of a set of provider core routers). A single common key set is expected to be used to authenticate all RSVP messages.
Interface, or neighbor configuration mode, is optimal when a router belongs to more than one security domain. For example, a provider router is adjacent to the provider edge (PE), or a PE is adjacent to an edge device. Different keys can be used but not shared.
Global configuration mode configures the defaults for interface and neighbor interface modes. These modes, unless explicitly configured, inherit the parameters from global configuration mode, as follows:
Window-size is set to 1.
Lifetime is set to 1800.
key-source key-chain command is set to none or disabled.
Global, Interface, and Neighbor Authentication Modes
You can configure global defaults for all authentication parameters including key, window size, and lifetime. These defaults are inherited when you configure authentication for each neighbor or interface. However, you can also configure these parameters individually on a neighbor or interface basis, in which case the global values (configured or default) are no longer inherited.
RSVP uses the following rules when choosing which authentication parameter to use when that parameter is configured at multiple levels (interface, neighbor, or global). RSVP goes from the most specific to least specific; that is, neighbor, interface, and global.
Global keys simplify the configuration and eliminate the chances of a key mismatch when receiving messages from multiple neighbors and multiple interfaces. However, global keys do not provide the best security.
Interface keys are used to secure specific interfaces between two RSVP neighbors. Because many of the RSVP messages are IP routed, there are many scenarios in which using interface keys are not recommended. If all keys on the interfaces are not the same, there is a risk of a key mismatch for the following reasons:
When the RSVP graceful restart is enabled, RSVP hello messages are sent with a source IP address of the local router ID and a destination IP address of the neighbor router ID. Because multiple routes can exist between the two neighbors, the RSVP hello message can traverse to different interfaces.
When the RSVP fast reroute (FRR) is active, the RSVP Path and Resv messages can traverse multiple interfaces.
When Generalized Multiprotocol Label Switching (GMPLS) optical tunnels are configured, RSVP messages are exchanged with router IDs as the source and destination IP addresses. Since multiple control channels can exist between the two neighbors, the RSVP messages can traverse different interfaces.
Neighbor-based keys are particularly useful in a network in which some neighbors support RSVP authentication procedures and others do not. When the neighbor-based keys are configured for a particular neighbor, you are advised to configure all the neighbor’s addresses and router IDs for RSVP authentication.
A security association (SA) is defined as a collection of information that is required to maintain secure communications with a peer to counter replay attacks, spoofing, and packet corruption.
This table lists the main parameters that define a security association.
Table 1 Security Association Main Parameters
IP address of the sender.
IP address of the final destination.
Interface of the SA.
Send or receive type of the SA.
Expiration timer value that is used to collect unused security association data.
Last sequence number that was either sent or accepted (dependent of the direction type).
Source of keys for the configurable parameter.
Key number (returned form the key-source) that was last used.
Algorithm last used (returned from the key-source).
Specifies the tolerance for the configurable parameter. The parameter is applicable when the direction parameter is the receive type.
Specifies the last window size value sequence number that is received or accepted. The parameter is applicable when the direction parameter is the receive type.
An SA is created dynamically when sending and receiving messages that require authentication. The neighbor, source, and destination addresses are obtained either from the IP header or from an RSVP object, such as a HOP object, and whether the message is incoming or outgoing.
When the SA is created, an expiration timer is created. When the SA authenticates a message, it is marked as recently used. The lifetime timer periodically checks if the SA is being used. If so, the flag is cleared and is cleaned up for the next period unless it is marked again.
This table shows how to locate the source and destination address keys for an SA that is based on the message type.
Table 2 Source and Destination Address Locations for Different Message Types
The key-source key-chain is used to specify which keys to use.
You configure a list of keys with specific IDs and have different lifetimes so that keys are changed at predetermined intervals automatically, without any disruption of service. Rollover enhances network security by minimizing the problems that could result if an untrusted source obtained, deduced, or guessed the current key.
RSVP handles rollover by using the following key ID types:
On TX, use the youngest eligible key ID.
On RX, use the key ID that is received in an integrity object.
For more information about implementing keychain management, see Cisco ASR 9000 Series RouterSystem Security Configuration Guide Cisco ASR 9000 Series Router.
When RSVP messages traverse multiple interface types with different maximum transmission unit (MTU) values, some messages can become out-of-sequence if they are fragmented.
Packets with some IP options may be reordered.
Change in QoS configurations may lead to a transient reorder of packets.
QoS policies can cause a reorder of packets in a steady state.
Because all out-of-sequence messages are dropped, the sender must retransmit them. Because RSVP state timeouts are generally long, out-of-sequence messages during a transient state do not lead to a state timeout.
How to Implement RSVP
RSVP requires coordination among several routers, establishing exchange of RSVP messages to set up LSPs. Depending on the client application, RSVP requires some basic configuration, as described in these topics:
To configure traffic engineering tunnel bandwidth, you must first set up TE tunnels and configure the reserved bandwidth per interface (there is no need to configure bandwidth for the data channel or the control channel).
Cisco IOS XR software supports two MPLS DS-TE modes: Prestandard and IETF.
For prestandard DS-TE you do not need to configure bandwidth for the data channel or the control channel. There is no other specific RSVP configuration required for this application. When no RSVP bandwidth is specified for a particular interface, you can specify zero bandwidth in the LSP setup if it is configured under RSVP interface configuration mode or MPLS-TE configuration mode.
Perform this task to confirm DiffServ-TE bandwidth.
In RSVP global and subpools, reservable bandwidths are configured per interface to accommodate TE tunnels on the node. Available bandwidth from all configured bandwidth pools is advertised using IGP. RSVP signals the TE tunnel with appropriate bandwidth pool requirements.
In the example , the output represents an LSP from ingress (head) router 10.51.51.51 to egress (tail) router 172.16.70.70. The tunnel ID (also called the destination port) is 6.
If no states can be found for a session that should be up, verify the
application (for example, MPLS-TE ) to see if
everything is in order. If a session has one PSB but no RSB, this indicates
that either the Path message is not making it to the egress (tail) router or
the reservation message is not making it back to the router R1 in question.
Go to the downstream router R2 and display the session information:
If R2 has no PSB, either the path message is not making it to the
router or the path message is being rejected (for example, due to lack of
resources). If R2 has a PSB but no RSB, go to the next downstream router R3
to investigate. If R2 has a PSB and an RSB, this means the reservation is
not making it from R2 to R1 or is being rejected.
show rsvp countersmessagessummary
Verifies whether the RSVP message is being transmitted and received.
Verifies how many RSVP states have expired. Because RSVP uses a soft-state mechanism, some failures will lead to RSVP states to expire due to lack of refresh from the neighbor.
RP/0/RSP0/CPU0:router# show rsvp counters events
mgmtEthernet0/0/0/0 tunnel6 Expired Path states 0 Expired
Path states 0 Expired Resv states 0 Expired Resv states 0 NACKs received 0
NACKs received 0 POS0/3/0/0 POS0/3/0/1 Expired
Path states 0 Expired Path states 0 Expired Resv states 0 Expired Resv
states 0 NACKs received 0 NACKs received 0 POS0/3/0/2
POS0/3/0/3 Expired Path states 0 Expired Path
states 0 Expired Resv states 0 Expired Resv states 1 NACKs received 0 NACKs
show rsvp interfacetype interface-path-id [detail]
Verifies that refresh reduction is working on a particular interface.
RP/0/RSP0/CPU0:router# show rsvp neighbor detail
Global Neighbor: 220.127.116.11 Interface Neighbor: 18.104.22.168
Interface: POS0/0/0/0 Refresh Reduction: "Enabled" or "Disabled". Remote
epoch: 0xXXXXXXXX Out of order messages: 0 Retransmitted messages: 0
Interface Neighbor: 22.214.171.124 Interface: POS0/1/0/0 Refresh Reduction:
"Enabled" or "Disabled". Remote epoch: 0xXXXXXXXX Out of order messages: 0
Retransmitted messages: 0
The example shows the configuration of bandwidth on an interface using prestandard DS-TE mode. The example configures an interface for a reservable bandwidth of 7500, specifies the maximum bandwidth for one flow to be 1000 and adds a sub-pool bandwidth of 2000.
The example shows the configuration of bandwidth on an interface using MAM. The example shows how to limit the total of all RSVP reservations on POS interface 0/3/0/0 to 7500 kbps, and allows each single flow to reserve no more than 1000 kbps.
rsvp interface pos 0/3/0/0
bandwidth mam 7500 1000
The example shows the configuration of bandwidth on an interface using RDM. The example shows how to limit the total of all RSVP reservations on POS interface 0/3/0/0 to 7500 kbps, and allows each single flow to reserve no more than 1000 kbps.
Refresh Reduction and Reliable Messaging Configuration: Examples
Refresh reduction feature as defined by RFC 2961 is supported and enabled by default. The examples illustrate the configuration for the refresh reduction feature. Refresh reduction is used with a neighbor only if the neighbor supports it also.
Refresh Interval and the Number of Refresh Messages Configuration: Example
The example shows how to configure the refresh interval to 30 seconds on POS 0/3/0/0 and how to change the number of refresh messages the node can miss before cleaning up the state from the default value of 4 to 6.
Retransmit Time Used in Reliable Messaging Configuration: Example
The example shows how to set the retransmit timer to 2 seconds. To prevent unnecessary retransmits, the retransmit time value configured on the interface must be greater than the ACK hold time on its peer.
The example shows how to change the acknowledge hold time from the default value of 400 ms, to delay or speed up sending of ACKs, and the maximum acknowledgment message size from default size of 4096 bytes. The example shows how to change the acknowledge hold time from the default value of 400 ms and how to delay or speed up sending of ACKs. The maximum acknowledgment message default size is from 4096 bytes.
If the peer node does not support refresh reduction, or for any other reason you want to disable refresh reduction on an interface, the example shows how to disable refresh reduction on that interface.
RSVP graceful restart is configured globally or per interface (as are refresh-related parameters). These examples show how to enable graceful restart, set the restart time, and change the hello message interval.
The example shows when RSVP receives a Router Alert (RA) packet from source address 126.96.36.199 and 188.8.131.52 is not a local address. The packet is forwarded with IP TTL decremented. Packets destined to 184.108.40.206 are dropped. All other RA packets are processed as normal RSVP packets.
show run ipv4 access-list
ipv4 access-list rsvpacl
10 permit ip host 220.127.116.11 any
20 deny ip any host 18.104.22.168
show run rsvp
signalling prefix-filtering access-list rsvpacl
RSVP Authentication by Using All the Modes: Example
The configuration example shows how to perform the following functions:
Authenticates all RSVP messages.
Authenticates the RSVP messages to or from 10.0.0.1 by setting the keychain for the key-source key-chain command to nbr_keys, SA lifetime is set to 3600, and the default window-size is set to 1.
Authenticates the RSVP messages not to or from 10.0.0.1 by setting the keychain for the key-source key-chain command to default_keys, SA lifetime is set to 3600, and the window-size is set 64 when using GigabitEthernet0/6/0/0; otherwise, the default value of 1 is used.
If a keychain does not exist or contain valid keys, this is considered a configuration error because signaling fails. However, this can be intended to prevent signaling. For example, when using the above configuration, if the nbr_keys does not contain valid keys, all signaling with 10.0.0.1 fails.
Generalized Multiprotocol Label Switching (GMPLS) User-Network Interface (UNI): Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Support for the Overlay Model
RSVP-TE Extensions in Support of End-to-End Generalized Multi-Protocol Label Switching (GMPLS) Recovery
Exclude Routes - Extension to Resource ReserVation Protocol-Traffic Engineering (RSVP-TE)
Generalized Labels for Lambda-Switch-Capable (LSC) Label Switching Routers
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