Manuals+

RSVP-Previous Hop Overwrite

Last Updated: January 12, 2012

The RSVP-Previous Hop Overwrite feature allows you to configure a Resource Reservation Protocol (RSVP) router, on a per interface basis, to populate an address other than the native interface address in the previous hop (PHOP) address field of the PHOP object when forwarding a PATH message onto that interface. You can configure the actual address for the router to use or an interface, including a loopback, from which to borrow the address.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Prerequisites for RSVP-Previous Hop Overwrite

You must configure RSVP on one or more interfaces on at least two neighboring routers that share a link within the network.

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Restrictions for RSVP-Previous Hop Overwrite

Information About RSVP-Previous Hop Overwrite

Feature Overview of RSVP-Previous Hop Overwrite

An RSVP PATH message contains a PHOP object that is rewritten at every RSVP hop. The object's purpose is to enable an RSVP router (R1) sending a PATH message to convey to the next RSVP router (R2) downstream that the previous RSVP hop is R1. R2 uses this information to forward the corresponding RESV message upstream hop-by-hop towards the sender.

The current behavior in Cisco IOS software is that an RSVP router always sets the PHOP address to the IP address of the egress interface onto which the router transmits the PATH message.

There are situations where, although some IP addresses of R1 are reachable, the IP address of its egress interface is not reachable from a remote RSVP router R2. This results in the corresponding RESV message generated by R2 never reaching R1 and the reservation never being established.

The figure below shows a sample network in which the preceding scenario occurs and no reservation is established.

Figure 1: Sample PHOP Network with Unified Communications Manager (CM)

This diagram illustrates a network with two branch offices, CE1 and CE2, connected via PE1 and PE2 routers through an MPLS VPN. It shows RSVP working between CE1 and CE2 when configured correctly, and failing when the egress interface IP address is unroutable.

Benefits of RSVP-Previous Hop Overwrite

Flexibility and Customization

You can configure a CE to populate the PHOP object in a PATH message with an address that is reachable in the customer VPN. This enables the RESV message to find its way back towards the sender so that reservations can be established.

How to Configure RSVP-Previous Hop Overwrite

How to Configure RSVP-Previous Hop Overwrite

Configuring a Source Address or a Source Interface

Perform this task to configure a source address or a source interface.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface type number
  4. ip rsvp bandwidth [interface-kbps] [single-flow-kbps]
  5. ip rsvp source {address ip-address | interface type number}
  6. end

DETAILED STEPS

Command or Action Purpose
Step 1 enable Enables privileged EXEC mode.
[Note] Enter your password if prompted.
Step 2 configure terminal Enters global configuration mode.
Step 3 interface type number Configures the interface type and enters interface configuration mode.
Step 4 ip rsvp bandwidth [interface-kbps] [single-flow-kbps] Enables RSVP on an interface.
[Note] The optional interface-kbps and single-flow-kbps arguments specify the amount of bandwidth that can be allocated by RSVP flows or to a single flow, respectively. Values are from 1 to 10000000.
[Note] Repeat this command for each interface on which you want to enable RSVP.
Step 5 ip rsvp source {address ip-address | interface type number} Configures an RSVP router to populate an address other than the native interface address in the PHOP address field of the hop object when forwarding a PATH message onto that interface.
[Note] The source IP address that you configure should be a valid local IP address.
Step 6 end (Optional) Returns to privileged EXEC mode.

Verifying the PHOP Configuration

[Note] You can use the following show command in user EXEC or privileged EXEC mode.

SUMMARY STEPS

  1. enable
  2. show ip rsvp interface [detail] [interface-type interface-number]
  3. exit

DETAILED STEPS

Command or Action Purpose
Step 1 enable (Optional) Enables privileged EXEC mode.
[Note] Enter your password if prompted.
[Note] Skip this step if you are using the show command in user EXEC mode.
Step 2 show ip rsvp interface [detail] [interface-type interface-number] (Optional) Displays RSVP-related interface information.
[Note] The optional keywords and arguments display additional information.
Step 3 exit (Optional) Exits privileged EXEC mode and returns to user EXEC mode.

Configuration Examples for RSVP-Previous Hop Overwrite

Examples Configuring RSVP-Previous Hop Overwrite

The figure below shows a sample network in which PHOP is configured.

Figure 2: Sample PHOP Network

This diagram shows a more detailed network topology with routers CE1, CE2, PE1, PE2, C1, and C2, illustrating IP addresses and interface connections for configuring RSVP-Previous Hop Overwrite.

Configuring a Source Address on Router CE1 for the CE1-to-PE1 Interface

The following example configures a source address on the CE1-to-PE1 (Ethernet 1/0) interface in the figure above:

Router (CE1) # configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router (CE1) (config)# interface ethernet 1/0
Router (CE1) (config-if)# ip rsvp source address 10.2.2.2
Router (CE1) (config-if)# end

Configuring a Source Address on Router CE2 for the CE2-to-PE2 Interface

The following example configures a source address on the CE2-to-PE2 (Ethernet 0/0) interface in the figure above:

Router (CE2) # configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router (CE2) (config)# interface ethernet 0/0
Router (CE2) (config-if)# ip rsvp source address 10.6.6.6
Router (CE2) (config-if)# end

Creating a Listener Proxy on Router C2

The following example creates a listener proxy on Router C2 and requests that the receiver reply with a RESV message for the flow if the PATH message destination is 10.7.7.7 in the figure above:

Router (C2) # configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router (C2) (config)# ip rsvp listener 10.7.7.7 any any reply
Router (C2) (config)# end

Creating a Session from Router C1 to Router C2

The following example creates an RSVP session from Router C1 to Router C2:

Router (C1) # configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router (C1) (config)# ip rsvp sender-host 10.7.7.7 10.1.1.1 UDP 100 200 1 1
Router (C1) (config)# end

Examples Verifying RSVP-Previous Hop Overwrite Configuration

Verifying the Source Address on Router CE1 for the CE1-to-PE1 Interface

The following example verifies the source address (10.2.2.2) configured on the CE1-to-PE1 (Ethernet 1/0) interface in the figure below:

Router (CE1) # show ip rsvp interface detail ethernet 1/0
Et1/0:
RSVP: Enabled
Interface State: Up
Bandwidth:
Curr allocated: 1K bits/sec
Max. allowed (total): 100K bits/sec
Max. allowed (per flow): 100K bits/sec
Max. allowed for LSP tunnels using sub-pools: 0 bits/sec
Set aside by policy (total): 0 bits/sec
Admission Control:
Header Compression methods supported:
rtp (36 bytes-saved), udp (20 bytes-saved)
Traffic Control:
RSVP Data Packet Classification is ON via CEF callbacks
Signalling:
DSCP value used in RSVP msgs: 0x3F
Number of refresh intervals to enforce blockade state: 4
Ip address used in RSVP objects: 10.2.2.2
Authentication: disabled
Key chain: <none>
Type: md5
Window size: 1
Challenge: disabled
Hello Extension: State: Disabled

Verifying the Source Address on Router CE2 for the CE2-to-PE2 Interface

The following example verifies the source address configured on the CE2-to-PE2 (Ethernet 0/0) interface in the figure below:

Router (CE2) # show ip rsvp interface detail ethernet 0/0
Et0/0:
RSVP: Enabled
Interface State: Up
Bandwidth:
Curr allocated: 0 bits/sec
Max. allowed (total): 100K bits/sec
Max. allowed (per flow): 100K bits/sec
Max. allowed for LSP tunnels using sub-pools: 0 bits/sec
Set aside by policy (total): 0 bits/sec
Admission Control:
Header Compression methods supported:
rtp (36 bytes-saved), udp (20 bytes-saved)
Traffic Control:
RSVP Data Packet Classification is ON via CEF callbacks
Signalling:
DSCP value used in RSVP msgs: 0x3F
Number of refresh intervals to enforce blockade state: 4
Ip address used in RSVP objects: 10.6.6.6
Authentication: disabled
Key chain: <none>
Type: md5
Window size: 1
Challenge: disabled
Hello Extension: State: Disabled

Verifying the Listener Proxy on Router C2

The following example verifies the listener proxy configured on Router C2 in the figure below:

Router (C2) # show ip rsvp listeners
To          Protocol DPort    Description   Action
10.7.7.7    any      any      RSVP Proxy    reply

Verifying the Session from Router C1 to Router C2

The following example verifies that the session configured between Router C1 and Router C2 in the figure below is up:

Router (C1) # show ip rsvp reservation
To          From     Pro DPort Sport Next Hop    I/F    Fi Serv BPS
10.7.7.7    10.1.1.1 UDP 100 200 10.1.2.21 Et0/0 FF RATE 1K

Verifying the PHOP Address

The following example on Router CE2 verifies the source address configured on the CE1-to-PE1 interface in the figure below as the PHOP address:

Router (CE2) # show ip rsvp sender detail
PATH:
Destination 10.7.7.7, Protocol Id 17, Don't Police , DstPort 100
Sender address: 10.1.1.1, port: 200
Path refreshes:
arriving: from PHOP 10.2.2.2 on Et0/0 every 30000 msecs
Traffic params - Rate: 1K bits/sec, Max. burst: 1K bytes
Min Policed Unit: 0 bytes, Max Pkt Size 2147483647 bytes
Path ID handle: CA000406.
Incoming policy: Accepted. Policy source(s): Default
Status:
Output on Ethernet1/0. Policy status: Forwarding. Handle: 0E000402
Policy source(s): Default

Verifying the Next-Hop Address

The following example on Router CE1 verifies the source address configured on the CE2-to-PE2 interface in the figure below as the next-hop address:

Router (CE1) # show ip rsvp reservation detail
RSVP Reservation. Destination is 10.7.7.7, Source is 10.1.1.1,
Protocol is UDP, Destination port is 100, Source port is 200
Next Hop: 10.6.6.6 on Ethernet1/0
Reservation Style is Fixed-Filter, QoS Service is Guaranteed-Rate
Resv ID handle: 03000400.
Created: 07:01:40 IST Tue Mar 25 2008
Average Bitrate is 1K bits/sec, Maximum Burst is 1K bytes
Min Policed Unit: 0 bytes, Max Pkt Size: 0 bytes
Status:
Policy: Forwarding. Policy source(s): Default

Additional References

The following sections provide references related to the RSVP-Previous Hop Overwrite feature.

Related Documents

Related Topic Document Title
Cisco IOS commands Cisco IOS Master Commands List, All Releases
QoS commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples Cisco IOS Quality of Service Solutions Command Reference
QoS features including signaling, classification, and congestion management "Quality of Service Overview" module

Standards

Standard Title
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

MIBs

MIB MIBs Link
No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature. To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: http://www.cisco.com/go/mibs

RFCs

RFC Title
RFC 2205 Resource ReSerVation Protocol (RSVP)--Version 1 Functional Specification
RFC 2209 Resource ReSerVation Protocol (RSVP)--Version 1 Message Processing Rules
RFC 3209 RSVP-TE: Extensions to RSVP for LSP Tunnels

Technical Assistance

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

Link: http://www.cisco.com/cisco/web/support/index.html

Feature Information for RSVP-Previous Hop Overwrite

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Table 1: Feature Information for RSVP-Previous Hop Overwrite
Feature Name Releases Feature Information
RSVP-Previous Hop Overwrite 12.4(20)T
15.0(1)SY		 The RSVP-Previous Hop Overwrite feature allows you to configure a Resource Reservation Protocol (RSVP) router, on a per interface basis, to populate an address other than the native interface address in the previous hop (PHOP) address field of the PHOP object when forwarding a PATH message onto that interface. You can configure the actual address for the router to use, or an interface, including a loopback, from which to borrow the address.
The following commands were introduced or modified: debug ip rsvp, ip rsvp source, show ip rsvp interface.

Glossary

QoS -- quality of service. A measure of performance for a transmission system that reflects its transmission quality and service availability.

RSVP -- Resource Reservation Protocol. A protocol that supports the reservation of resources across an IP network. Applications running on IP end systems can use RSVP to indicate to other nodes the nature (bandwidth, jitter, maximum burst, and so on) of the packet streams that they want to receive.

RSVP Agent -- Implements a Resource Reservation Protocol (RSVP) agent on Cisco IOS voice gateways that support Unified CM.

Unified Communications Manager (CM) -- The software-based, call-processing component of the Cisco IP telephony solution. The software extends enterprise telephony features and functions to packet telephony network devices such as IP phones, media processing devices, voice-over-IP (VoIP) gateways, and multimedia applications.

Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks.

Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R)

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

© 2012 Cisco Systems, Inc. All rights reserved.

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