Table Of Contents
VoIP Interoperability with Cisco Express Forwarding and Policy-Based Routing
VoIP and Cisco Express Forwarding Interoperability Overview
VoIP and Policy-Based Routing Interoperability Overview
When To Use Policy-Based Routing
Configuring Standard IP Access Lists
Enabling Policy-Based Routing on a Loopback Interface
Enabling Policy-Based Routing for VoIP Signaling Packets
Configuring Voice Class Source Interface
Configuring Source Interface Loopback for MGCP
FXS-to-FXS Call with Policy Based Routing and DSCP Marking (H.323 and SIP)
FXS-to-FXS call with Policy Based Routing and DSCP Marking (MGCP)
VoIP Interoperability with Cisco Express Forwarding and Policy-Based Routing
This document describes the VoIP Interoperability with Cisco Express Forwarding (CEF) and Policy-Based Routing (PBR) functionality supported on selected IOS gateway platforms in Cisco IOS 12.3. This functionality is supported in Cisco IOS Release 12.3 on the following platforms: Cisco IAD2420 series, Cisco 2600 series, Cisco 3620, Cisco 3640, Cisco 3660, Cisco 3700 series, and Cisco MC3810.
For a complete description of the CEF-related commands used in this chapter, refer to the Cisco IOS Switching Services Command Reference, Release 12.3. For a complete description of the PBR-related commands used in this chapter, refer to the Cisco IOS Quality of Service Solutions Command Reference, Release 12.3. To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.
This document includes the following sections:
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VoIP and Cisco Express Forwarding Interoperability Overview
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VoIP and Cisco Express Forwarding Interoperability Overview
This functionality enables Cisco Express Forwarding (CEF) of VoIP signaling and payload packets that originate from voice interfaces and interactive voice response (IVR) applications.
This feature modifies the Voice over IP (VoIP) and IVR programming so that they can interoperate with features that are supported only in the CEF path (not in the fast switching path that VoX uses). Voice and IVR only work in the fast path on the routers where they are originated and terminated (Voice and IVR on "transit" routers are just data packets and of course can be CEF switched).
Cisco Express Forwarding (CEF) is advanced Layer 3 IP switching technology. CEF optimizes network performance and scalability for networks with large and dynamic traffic patterns, such as the Internet, on networks characterized by intensive web-based applications, or interactive sessions.
Although you can use CEF in any part of a network, it is designed for high-performance, highly resilient Layer 3 IP backbone switching.
CEF Components
Information conventionally stored in a route cache is stored in several data structures for CEF switching. The data structures provide optimized lookup for efficient packet forwarding. The two main components of CEF operation are:
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Forwarding Information Base
CEF uses a Forwarding Information Base (FIB) to make IP destination prefix-based switching decisions. The FIB is conceptually similar to a routing table or information base. It maintains a mirror image of the forwarding information contained in the IP routing table. When routing or topology changes occur in the network, the IP routing table is updated, and those changes are reflected in the FIB. The FIB maintains next-hop address information based on the information in the IP routing table.
Because there is a one-to-one correlation between FIB entries and routing table entries, the FIB contains all known routes and eliminates the need for route cache maintenance that is associated with earlier switching paths such as fast switching and optimum switching.
Adjacency Tables
Network nodes in the network are said to be adjacent if they can reach each other with a single hop across a link layer. In addition to the FIB, CEF uses adjacency tables to prepend Layer 2 addressing information. The adjacency table maintains Layer 2 next-hop addresses for all FIB entries.
Adjacency Discovery
The adjacency table is populated as adjacencies are discovered. Each time an adjacency entry is created (such as through the ARP protocol), a link-layer header for that adjacent node is precomputed and stored in the adjacency table. When a route is determined, it points to a next hop and corresponding adjacency entry. It is subsequently used for encapsulation during CEF switching of packets.
Adjacency Resolution
A route might have several paths to a destination prefix, such as when a router is configured for simultaneous load balancing and redundancy. For each resolved path, a pointer is added for the adjacency corresponding to the next-hop interface for that path. This mechanism is used for load balancing across several paths.
Adjacency Types That Require Special Handling
In addition to adjacencies associated with next-hop interfaces (host-route adjacencies), other types of adjacencies are used to expedite switching when certain exception conditions exist. When the prefix is defined, prefixes requiring exception processing are cached with one of the special adjacencies listed in Table 1.
Unresolved Adjacency
When a link-layer header is prepended to packets, FIB requires the prepend to point to an adjacency corresponding to the next hop. If an adjacency was created by FIB and not discovered through a mechanism, such as ARP, the Layer 2 addressing information is not known and the adjacency is considered incomplete. After the Layer 2 information is known, the packet is forwarded to the route processor, and the adjacency is determined through ARP.
Supported Media
CEF supports ATM/AAL5 SNAP, ATM/AAL5mux, ATM/AAL5nlpid, Frame Relay, Ethernet, FDDI, PPP, HDLC, and tunnels.
Central CEF Mode
When CEF mode is enabled, the CEF FIB and adjacency tables reside on the route processor, and the route processor performs the express forwarding. You can use CEF mode when line cards are not available for CEF switching or when you need to use features not compatible with distributed CEF switching.
VoIP and Policy-Based Routing Interoperability Overview
This feature enables policy-based routing of VoIP traffic that originates or terminates on the specified voice gateways and introduces voice packet differentiated services code point (DSCP) marking for Media Gateway Control Protocol (MGCP) voice gateways.
PBR (policy-based routing) gives you a flexible means of routing packets by allowing you to configure a defined policy for traffic flows, lessening reliance on routes derived from routing protocols. To this end, PBR gives you more control over routing by extending and complementing the existing mechanisms provided by routing protocols. PBR allows you to set the IP precedence. It also allows you to specify a path for certain traffic, such as priority traffic over a high-cost link.
You can set up PBR as a way to route packets based on configured policies. For example, you can implement routing policies to allow or deny paths based on the identity of a particular end system, an application protocol, or the size of packets.
PBR allows you to perform the following tasks:
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Policies can be based on IP address, port numbers, protocols, or size of packets. For a simple policy, you can use any one of these descriptors; for a complicated policy, you can use all of them.
For example, classification of traffic through PBR allows you to identify traffic for different classes of service at the edge of the network and then implement quality of service (QoS) defined for each class of service (CoS) in the core of the network using priority queuing (PQ), custom queuing (CQ), or weighted fair queuing (WFQ) techniques. This process obviates the need to classify traffic explicitly at each wide-area network (WAN) interface in the core-backbone network.
How It Works
All packets received on an interface with PBR enabled are passed through enhanced packet filters known as route maps. The route maps used by PBR dictate the policy, determining to where the packets are forwarded.
Route maps are composed of statements. The route map statements can be marked as permit or deny, and they are interpreted in the following ways:
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You specify PBR on the interface that receives the packet, not on the interface from which the packet is sent.
When To Use Policy-Based Routing
You might enable PBR if you want certain packets to be routed some way other than the obvious shortest path. For example, PBR can be used to provide the following functionality:
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About Differentiated Services
Differentiated services (DiffServ) describes a set of end-to-end QoS (Quality of Service) capabilities. End-to-end QoS is the ability of the network to deliver service required by specific network traffic from one end of the network to another. Cisco IOS QoS software supports three types of service models: best-effort services, integrated services (IntServ), and differentiated services.
Differentiated services is a multiple service model that can satisfy differing QoS requirements. With Differentiated Services, the network tries to deliver a particular kind of service based on the QoS specified by each packet. This specification can occur in different ways, for example, using the 6-bit DSCP setting in IP packets or source and destination addresses. The network uses the QoS specification to classify, mark, shape, and police traffic, and to perform intelligent queuing.
Differentiated services is used for several mission-critical applications and for providing end-to-end QoS. Typically, Differentiated services is appropriate for aggregate flows because it performs a relatively coarse level of traffic classification.
DS Field Definition
A replacement header field, called the DS field, is defined by differentiated services. The DS field supersedes the existing definitions of the IPv4 type of service (ToS) octet (RFC 791) and the IPv6 traffic class octet. Six bits of the DS field are used as the DSCP to select the per hop behavior (PHB) at each interface. A currently unused (CU) 2-bit field is reserved for explicit congestion notification (ECN). The value of the CU bits is ignored by DS-compliant interfaces when determining the PHB to apply to a received packet.
Per-Hop Behaviors
RFC 2475 defines PHB as the externally observable forwarding behavior applied at a DiffServ-compliant node to a DiffServ behavior aggregate (BA).
With the ability of the system to mark packets according to DSCP setting, collections of packets with the same DSCP setting and sent in a specific direction can be grouped into a BA. Packets from multiple sources or applications can belong to the same BA.
In other words, a PHB refers to the packet scheduling, queuing, policing, or shaping behavior of a node on any given packet belonging to a BA, as configured by a service level agreement (SLA) or a policy map.
The following sections describe the four available standard PHBs:
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Default PHB
The default PHB essentially specifies that a packet marked with a DSCP value of 000000 (recommended) receives the traditional best-effort service from a DS-compliant node (that is, a network node that complies with all of the core DiffServ requirements). Also, if a packet arrives at a DS-compliant node, and the DSCP value is not mapped to any other PHB, the packet will get mapped to the default PHB.
Class-Selector PHB
To preserve backward-compatibility with any IP precedence scheme currently in use on the network, DiffServ has defined a DSCP value in the form xxx000, where x is either 0 or 1. These DSCP values are called class-selector code points. (The DSCP value for a packet with default PHB 000000 is also called the class-selector code point.)
The PHB associated with a class-selector code point is a class-selector PHB. These class-selector PHBs retain most of the forwarding behavior as nodes that implement IP Precedence-based classification and forwarding.
For example, packets with a DSCP value of 110000 (the equivalent of the IP precedence-based value of 110) have preferential forwarding treatment (for scheduling, queueing, and so on), as compared to packets with a DSCP value of 100000 (the equivalent of the precedence-based value of 100). These class-selector PHBs ensure that DS-compliant nodes can coexist with IP precedence-based nodes.
Assured Forwarding PHB
Assured Forwarding PHB is nearly equivalent to controlled load service available in the integrated services model. The AFny PHB defines a method by which BAs can be given different forwarding assurances.
For example, network traffic can be divided into the following classes:
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Further, the AFny PHB defines four assured forwarding classes: AF1, AF2, AF3, and AF4. Each class is assigned a specific amount of buffer space and interface bandwidth, according to the SLA with the service provider or policy map.
Within each assured forwarding class, you can specify three drop precedence (dP) values: 1, 2, and 3. Assured Forwarding PHB can be expressed as shown in the following example: AFny. In this example, n represents the assured forwarding class number (1, 2, or 3) and y represents the dP value (1, 2, or 3) within the AFn class.
In instances of network traffic congestion, if packets in a particular assured forwarding class (for example, AF1) need to be dropped, packets in the AF1 class will be dropped according to the following guideline:
dP(AFny) >= dP(AFnz) >= dP(AFnx)
where dP (AFny) is the probability that packets of the AFny class will be dropped. In other words, y denotes the dP within an AFn class.
In the following example, packets in the AF13 class will be dropped before packets in the AF12 class, which in turn will be dropped before packets in the AF11 class:
dP(AF13) >= dP (AF12) >= dP(AF11)
The dP method penalizes traffic flows within a particular BA that exceed the assigned bandwidth. Packets on these offending flows could be re-marked by a policer to a higher drop precedence.
An AFx class can be denoted by the DSCP value, xyzab0, where xyz can be 001, 010, 011, or 100, and ab represents the dP value.
Table 2 lists the DSCP value and corresponding dP value for each assured forwarding PHB class.
Expedited Forwarding PHB
Resource Reservation Protocol (RSVP), a component of the integrated services model, provides a Guaranteed Bandwidth Service. Applications such as VoIP, video, and online trading programs require this kind of robust service. The Expedited Forwarding (EF) PHB, a key ingredient of DiffServ, supplies this type of robust service by providing low loss, low latency, low jitter, and assured bandwidth service.
EF can be implemented using priority queueing (PQ), along with rate-limiting on the class (or BA). When implemented in a DiffServ network, EF PHB provides a virtual leased line, or premium service. For optimal efficiency, however, EF PHB should be reserved for only the most critical applications because, in instances of traffic congestion, it is not feasible to treat all or most traffic as high priority.
EF PHB is ideally suited for applications such as VoIP that require low bandwidth, guaranteed bandwidth, low delay, and low jitter.
Restrictions
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Configuration Tasks
See the following sections for configuration tasks for the VoIP Interoperability with Cisco Express Forwarding and policy-based routing feature. Each task in the list is identified as either required or optional.
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Configuring Standard IP Access Lists
To define a standard IP access list, use the following command beginning in global configuration mode.
Configuring IP Route Mapping
To enable route mapping, use the following commands beginning in global configuration mode:
Enabling Policy-Based Routing on a Loopback Interface
To enable policy-based routing on a loopback interface, use the following commands beginning in global configuration mode:
Enabling Policy-Based Routing for VoIP Signaling Packets
To enable policy-based routing for VoIP signaling packets, use the following commands beginning in global configuration mode:
Step 1
Router(config)# ip local policy route-map map-tag
Identifies the route map to use for local policy routing.
Configuring IP DSCP for VoIP
To set the DSCP for the quality of service, use the following commands starting in global configuration mode:
Step 1
Router(config)# dial-peer voice tag voip
Enters dial-peer configuration mode and specifies VoIP voice encapsulation.
Step 2
Router(config-dial-peer)# ip qos dscp [number | set-af | set-cs | default | ef]
[media | signaling]
Specifies IP DSCP.
The optional keywords and arguments are as follows:
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Configuring MGCP IP DSCP
To set the DSCP for the quality of service, use the following commands beginning in global configuration mode:
Configuring IP CEF (minimum)
To configure minimum IP Cisco Express Forwarding, use the following command starting in global configuration mode:
Configuring Voice Class Source Interface
To configure the dial peer source loopback interface to enable PBR for voice originating at this dial peer, use the following commands starting in global configuration mode:
Configuring Source Interface Loopback for MGCP
To configure the MGCP profile source loopback interface at this interface, use the following commands starting in global configuration mode:
Verifying the Configuration
To verify that CEF support and/or policy-based routing is configured correctly, enter the show running-config privileged EXEC command to display the command settings for the router, as shown in the "Configuration Examples" section.
Troubleshooting Tips
To display IP policy routing packet activity, use the debug ip policy command in privileged EXEC configuration mode.
Caution
The following is sample output from the debug ip policy command:
4d15h:IP:s=6.0.0.6 (local), d=10.0.0.1, len 331, policy match4d15h:IP:route map voice, item 10, permit4d15h:IP:s=6.0.0.6 (local), d=10.0.0.1 (Serial1/1), len 331, policyrouted4d15h:IP:local to Serial1/1 10.0.0.14d15h:IP:s=6.0.0.6 (local), d=10.0.0.1, len 40, policy match4d15h:IP:route map voice, item 10, permit4d15h:IP:s=6.0.0.6 (local), d=10.0.0.1 (Serial1/1), len 40, policyrouted4d15h:IP:local to Serial1/1 10.0.0.14d15h:IP:s=6.0.0.6 (local), d=10.0.0.1, len 40, policy match4d15h:IP:route map voice, item 10, permit4d15h:IP:s=6.0.0.6 (local), d=10.0.0.1 (Serial1/1), len 40, policyrouted4d15h:IP:local to Serial1/1 10.0.0.14d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed.....
Configuration Examples
The following are configuration examples for the topology shown in Figure 1:
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Figure 1 Example Topology
FXS-to-FXS Call with Policy Based Routing and DSCP Marking (H.323 and SIP)
The following are CE-1 and CE-2 configuration examples as shown in Figure 1:
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CE-1 Configuration
!ip cef!interface loopback0ip address 10.0.0.1 255.255.255.255ip policy route-map VoIP_PBRip route-cache policy!ip local policy route-map VoIP_PBR!access-list 101 permit udp any any range 16384 32767access-list 101 permit udp any range 16384 32767 anyaccess-list 101 permit tcp any any eq 1720access-list 101 permit tcp any eq 1720 any!route-map VoIP_PBR permit 10match ip address 101<set interface serial0/0 | set ip next-hop ...>!dial-peer voice 1 potsdestination-pattern 1111port 1/0/0!dial-peer voice 2 voipdestination-pattern 4444incoming called-number 1111session protocol <cisco | sipv2>session target ipv4:60.0.0.6ip qos dscp af31 signalingip qos dscp ef mediavoice-class source interface loopback0CE-2 Configuration
!ip cef!interface loopback0ip address 60.0.0.6 255.255.255.255ip policy route-map VoIP_PBRip route-cache policy!ip local policy route-map VoIP_PBR!access-list 101 permit udp any any range 16384 32767access-list 101 permit udp any range 16384 32767 anyaccess-list 101 permit tcp any any eq 1720access-list 101 permit tcp any eq 1720 any!route-map VoIP_PBR permit 10match ip address 101<set interface serial0/0 | set ip next-hop ...>!dial-peer voice 1 potsdestination-pattern 4444port 2/0/0!dial-peer voice 2 voipdestination-pattern 1111incoming called-number 4444session protocol <cisco | sipv2>session target ipv4:10.0.0.1ip qos dscp af31 signalingip qos dscp ef mediavoice-class source interface loopback0FXS-to-FXS call with Policy Based Routing and DSCP Marking (MGCP)
The following are CE-1 and CE-2 configuration examples as shown in Figure 1:
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CE-1 Configuration
!ip cef!interface loopback0ip address 10.0.0.1 255.255.255.255ip policy route-map VoIP_PBRip route-cache policy!ip local policy route-map VoIP_PBR!access-list 101 permit udp any any range 16384 32767access-list 101 permit udp any range 16384 32767 anyaccess-list 101 permit tcp any any eq 1720access-list 101 permit tcp any eq 1720 any!route-map VoIP_PBR permit 10match ip address 101<set interface serial0/0 | set ip next-hop ...>!mgcpmgcp call-agent 1.8.14.11 service-type mgcp version 0.1mgcp modem passthrough voip mode cano mgcp timer receive-rtcpmgcp ip qos dscp af31 signalingmgcp ip qos dscp ef mediamgcp profile defaultsource interface loopback0!dial-peer voice 1 potsapplication mgcpappport 1/0/0!CE-2 Configuration
!ip cef!interface loopback0ip address 60.0.0.6 255.255.255.255ip policy route-map VoIP_PBRip route-cache policy!ip local policy route-map VoIP_PBR!access-list 101 permit udp any any range 16384 32767access-list 101 permit udp any range 16384 32767 anyaccess-list 101 permit tcp any any eq 1720access-list 101 permit tcp any eq 1720 any!route-map VoIP_PBR permit 10match ip address 101<set interface serial0/0 | set ip next-hop ...>!mgcpmgcp call-agent 1.8.14.11 service-type mgcp version 0.1mgcp modem passthrough voip mode camgcp default-package line-packageno mgcp timer receive-rtcpmgcp ip qos dscp af31 signalingmgcp ip qos dscp ef mediamgcp profile defaultsource interface loopback0!dial-peer voice 1 potsapplication mgcpappport 2/0/0!Command Reference
The following commands are described in this section:
debug ip policy
To display IP policy routing packet activity, use the debug ip policy command in privileged EXEC configuration mode. The no form of this command disables debugging output.
debug ip policy [access-list-name]
no debug ip policy
Syntax Description
Defaults
This command is not enabled.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
After you configure IP policy routing with the ip policy and route-map commands, use the debug ip policy command to ensure that the IP policy is configured correctly.
Policy routing looks at various parts of the packet and then routes the packet based on certain user-defined attributes in the packet.
The debug ip policy command helps you determine what policy routing is following. It displays information about whether a packet matches the criteria, and if so, the resulting routing information for the packet.
Caution
Examples
The following is sample output from the debug ip policy command:
4d15h:IP:s=6.0.0.6 (local), d=10.0.0.1, len 331, policy match4d15h:IP:route map voice, item 10, permit4d15h:IP:s=6.0.0.6 (local), d=10.0.0.1 (Serial1/1), len 331, policyrouted4d15h:IP:local to Serial1/1 10.0.0.14d15h:IP:s=6.0.0.6 (local), d=10.0.0.1, len 40, policy match4d15h:IP:route map voice, item 10, permit4d15h:IP:s=6.0.0.6 (local), d=10.0.0.1 (Serial1/1), len 40, policyrouted4d15h:IP:local to Serial1/1 10.0.0.14d15h:IP:s=6.0.0.6 (local), d=10.0.0.1, len 40, policy match4d15h:IP:route map voice, item 10, permit4d15h:IP:s=6.0.0.6 (local), d=10.0.0.1 (Serial1/1), len 40, policyrouted4d15h:IP:local to Serial1/1 10.0.0.14d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1, len 60, FIB policy match4d15h:IP:s=60.0.0.6 (Loopback0), d=2.0.0.1 (Serial1/1), len 60, FIBpolicy routed.....
ip cef
To enable Cisco Express Forwarding (CEF) on the route processor card, use the ip cef command in global configuration mode. To disable CEF, use the no form of this command.
ip cef [accounting | load-sharing | table type | traffic-statistics]
no ip cef [accounting | load-sharing | table type | traffic-statistics]
Syntax Description
Defaults
CEF is disabled by default.
Command Modes
Global configuration
Command History
Usage Guidelines
Use the ip cef command to control whether voice is switched on the router.
Examples
The following example shows ip cef configured for load sharing using the original algorithm:
ip cef load-sharing algorithm originalRelated Commands
mgcp ip qos dscp
To set the differentiated services code point (DSCP) for the quality of service, use the mgcp ip qos dscp command in global configuration mode. To enable the default, use the no form of this command.
mgcp ip qos dscp [number | set-af | set-cs | default | ef] [media | signaling]
no mgcp ip qos dscp [number | set-af | set-cs | default | ef] [media | signaling]
Syntax Description
Defaults
For signaling DSCP is set to bit pattern af31 for voice ef.
Command Modes
Global configuration
Command History
Usage Guidelines
To configure voice and signaling traffic priorities for MGCP, use the mgcp ip qos dscp command.
Recommended values are mgcp ip qos dscp ef media and mgcp ip qos dscp af31 signaling
Examples
The following example specifies DSCP is set to precedence 1 and is applied to media payload packets.
dial-peer voice 1 voipmgcp ip qos dscp cs1 mediaRelated Commands
source interface
To configure the MGCP profile source loopback interface at this interface, use the source interface command in MGCP profile configuration mode. To remove the loopback interface, use the no form of this command.
source interface loopback int_name
no source interface
Syntax Description
loopback
Configures the loopback interface.
int_name
Defines the name of the loopback interface. Valid entries for int-name are from 0 to 2147483647.
Defaults
No loopback is configured.
Command Modes
MGCP profile configuration
Command History
Usage Guidelines
To specify a loopback interface to be used for policy-based routing of all media traffic specified by a specific MGCP profile, use the MGCP profile source interface command.
Examples
The following example shows the loopback configured at the interface designated 0:
mgcp profile defaultsource interface loopback 0voice-class source interface
To configures the dial peer source interface parameter to loopback, use the voice-class source interface command in dial-peer voice configuration mode. To remove the loopback interface, use the no form of this command.
voice-class source interface loopback int-name
no voice-class source interface
Syntax Description
loopback
Configures the loopback interface.
int-name
Defines the name of the loopback interface. Valid entries are from 0 through 2147483647.
Defaults
No loopback is configured.
Command Modes
Dial-peer voice configuration
Command History
Usage Guidelines
To specify a loopback interface to be used for policy-based routing of all media traffic traveling through a specific dial peer, use the dial-peer voice-class source interface command.
Examples
The following example shows the loopback configured at the interface designated 0:dial-peer voice 1 voipvoice-class source interface loopback 0ip qos dscp
To set the differentiated services code point (DSCP) for the quality of service, use the ip qos dscp command in dial-peer configuration mode. To disable DSCP, use the no form of this command.
ip qos dscp [number | set-af | set-cs | default | ef] [media | signaling]
no ip qos dscp [number | set-af | set-cs | default | ef] [media | signaling]
Syntax Description
Defaults
DSCP is set to bit pattern 000000.
Command Modes
Dial-peer configuration
Command History
Usage Guidelines
To configure voice and signaling traffic priorities for SIP and H.323, use the ip qos dscp command.
Recommended values are ip qos dscp ef media and ip qos dscp af31 signaling
Examples
The following example specifies DSCP is set to precedence 1 and is applied to media payload packets.
dial-peer voice 1 voipip qos dscp cs1 mediaRelated Commands
Glossary
AAL5—ATM adaptation layer 5. One of four AALs recommended by the ITU-T. AAL5 supports connection-oriented VBR services and is used predominantly for the transfer of classical IP over ATM and LANE traffic. AAL5 uses SEAL and is the least complex of the current AAL recommendations. It offers low bandwidth overhead and simpler processing requirements in exchange for reduced bandwidth capacity and error-recovery capability.
BA—
CEF—Cisco Express Forwarding. Layer 3 switching technology. CEF can also refer to central CEF mode, one of the two modes of CEF operation that enables a route processor to perform express forwarding
CQ—customer queue.
CLI—command-line interface. An interface that allows the user to interact with the operating system by entering commands and optional arguments. The UNIX operating system and DOS provide CLIs.
dCEF—Distributed CEF. One of two modes of CEF operation that enables line cards to perform the express forwarding between port adapters.
DSCP—Differentiated Services Code Point. An IP packet classification mechanism
DSP—digital signal processor. A DSP segments the voice signal into frames and stores them in voice packets.
FIB—Forwarding Information Base. A component of CEF. It is the lookup table the router uses to make destination-based switching decisions during CEF operation. It maintains a mirror image of the forwarding information stored in the IP routing table.
IVR—interactive voice response. Term used to describe systems that provide information in the form of recorded messages over telephone lines in response to user input in the form of spoken words or, more commonly, DTMF signaling. Examples include banks that allow you to check your balance from any telephone and automated stock quote systems.
MGCP—Media Gateway Control Protocol. A merging of the IPDC and SGCP protocols.
MPLS—Multiprotocol Label Switching. Switching method that forwards IP traffic using a label. This label instructs the routers and the switches in the network where to forward the packets based on preestablished IP routing information.
PBR—policy based routing. Routing scheme that forwards packets to specific interfaces based on user-configured policies. Such policies might specify that traffic sent from a particular network should be forwarded out one interface, and all other traffic should be forwarded out another interface.
PQ—priority queue. Routing feature in which frames in an output queue are prioritized based on various characteristics, such as packet size and interface type.
VoIP—Voice over IP. The capability to carry normal telephony-style voice over an IP-based internet with POTS-like functionality, reliability, and voice quality. VoIP enables a router to carry voice traffic (for example, telephone calls and faxes) over an IP network. In VoIP, the DSP segments the voice signal into frames, which then are coupled in groups of two and stored in voice packets. These voice packets are transported using IP in compliance with ITU-T specification H.323.
WAN—wide-area network. Data communications network that serves users across a broad geographic area and often uses transmission devices provided by common carriers. Frame Relay, SMDS, and X.25 are examples of WANs
WFQ—weighted fair queuing. Congestion management algorithm that identifies conversations (in the form of traffic streams), separates packets that belong to each conversation, and ensures that capacity is shared fairly between these individual conversations. WFQ is an automatic way of stabilizing network behavior during congestion and results in increased performance and reduced retransmission
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