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Frame Relay was conceived as a protocol for use over serial interfaces and was designed for networks with large T1 installations. This chapter describes the tasks for configuring Frame Relay on the access server. For a complete description of the commands mentioned in this chapter, refer to the "Frame Relay Commands" chapter in the Access and Communication Servers Command Reference publication.
Although Frame Relay access was originally restricted to leased lines, dial-up access is now supported. For more information, see the "Configure DDR over Frame Relay" section in the "Configuring DDR" chapter of this publication.
To install software on a new access server by downloading software from a central server over an interface that supports Frame Relay, see the "Loading System Images, Microcode Images, and Configuration Files" chapter in this publication.
Cisco's Frame Relay implementation currently supports access servers on IP, AppleTalk, and Novell IPX.
The Frame Relay software provides the following capabilities:
One of the following hardware configurations is possible for Frame Relay connections:
The CSU/DSU converts V.35 or RS-449 signals to the properly coded T1 transmission signal for successful reception by the Frame Relay network. Figure 9-1 illustrates the connections between the different components.
The Frame Relay interface actually consists of one physical connection between the network server and the switch that provides the service. This single physical connection provides direct connectivity to each device on a network, such as a StrataCom FastPacket wide-area network.
You must follow certain basic steps to enable Frame Relay for your network. In addition, you can customize Frame Relay for your particular network needs, set local and multicast DLCIs in test environments, and monitor Frame Relay connections. The first three tasks in the following list are required.
The following sections describe these tasks. See the examples at the end of this chapter for ideas of how to configure Frame Relay on your network. See the "Frame Relay Commands" chapter in the Access and Communication Servers Command Reference publication for information about the commands listed in the tasks.
To set Frame Relay encapsulation at the interface level, perform the following tasks beginning in global configuration mode:
| Task | Command |
|---|---|
| Specify the serial interface, and enter interface configuration mode. | interface serial number1 |
| Enable Frame Relay and specify the encapsulation method. | encapsulation frame-relay [ietf] |
Frame Relay supports encapsulation of all supported protocols except bridging in conformance with RFC 1294, allowing interoperability between multiple vendors. Use the IETF form of Frame Relay encapsulation if your access server is connected to another vendor's equipment across a Frame Relay network. IETF encapsulation is supported at either the interface level or on a per-DLCI (map entry) basis.
For an example of how to enable Frame Relay and set the encapsulation method, see the sections "IETF Encapsulation Example" and "Static Address Mapping Examples" later in this chapter.
Dynamic address mapping uses Frame Relay Inverse ARP to request the next-hop protocol address for a specific connection, given its known DLCI. Responses to Inverse ARP requests are entered in an address-to-DLCI mapping table on the access server; the table is then used to supply the next-hop protocol address or the DLCI for outgoing traffic.
Inverse ARP is enabled by default for all protocols it supports, but can be disabled for specific protocol-DLCI pairs. As a result, you can use dynamic mapping for some protocols and static mapping for other protocols on the same DLCI. You can explicitly disable Inverse ARP for a protocol-DLCI pair if you know the protocol is not supported on the other end of the connection. See the "Disable or Reenable Frame Relay Inverse ARP" section later in this chapter for more information.
Because Inverse ARP is enabled by default for all protocols that it supports, no additional command is required to configure dynamic mapping on an interface.
A static map links a specified next-hop protocol address to a specified DLCI. Static mapping removes the need for Inverse ARP requests; when you supply a static map, Inverse ARP is automatically disabled for the specified protocol on the specified DLCI.
You must use static mapping if the access server at the other end either does not support Inverse ARP at all or does not support Inverse ARP for a specific protocol that you want to use over Frame Relay.
To establish static mapping according to your network needs, perform one of the following tasks in interface configuration mode:
| Task | Command |
|---|---|
| Define the mapping between a next-hop protocol address and the DLCI used to connect to the address. | frame-relay map protocol protocol-address dlci [broadcast] [ietf] [cisco] |
The supported protocols and the corresponding keywords to enable them are as follows:
You can greatly simplify the configuration for the Open Shortest Path First (OSPF) protocol by adding the optional broadcast keyword when doing this task. See the frame-relay map description in the Access and Communication Servers Command Reference publication and the examples at the end of this chapter for more information about using the broadcast keyword.
For examples of how to establish static address mapping, see the "Static Address Mapping Examples" section later in this chapter.
Our Frame Relay software supports the industry-accepted standards for addressing the Local Management Interface (LMI), including the Cisco specification. To configure the LMI, complete the tasks in the following sections. The tasks in the first two sections are required.
If the access server is attached to a public data network, the LMI type must match the type used on the public network. Otherwise, you can select an LMI type to suit the needs of your private Frame Relay network.
You can set one of three types of LMIs on our access server: ANSI T1.617 Annex D, Cisco, and ITU-T Q.933 Annex A. To do so, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
| Set the LMI type. | frame-relay lmi-type {ansi | cisco | q933a} |
The default LMI type is cisco.
For an example of how to set the LMI type, see the "Pure Frame Relay DCE Example" section later in this chapter.
A keepalive interval must be set to enable the LMI. By default, this interval is ten seconds and, per the LMI protocol, must be less than the corresponding interval on the switch. To set the keepalive interval, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
| Set the keepalive interval. | frame-relay keepalive number |
| Turn off keepalives on networks without an LMI. | no frame-relay keepalive |
This command has the same effect as the keepalive interface configuration command.
For an example of how to specify an LMI keepalive interval, see the "Two Access Servers in Static Mode Example" section later in this chapter.
You can set various optional counters, intervals, and thresholds to fine-tune the operation of your LMI DTE and DCE devices. Set these attributes by performing one or more of the following tasks in interface configuration mode:
See the "Frame Relay Commands" chapter in the Access and Communication Servers Command Reference publication for details about commands used to set the polling and timing intervals.
Perform the tasks in the following sections to customize Frame Relay:
To understand and define Frame Relay Subinterfaces, perform the tasks in the following sections:
After these tasks are completed, you can also perform the following optional task:
For an example of how to define a subinterface, see the section "Subinterface Examples" later in this chapter.
Frame Relay subinterfaces provide a mechanism for supporting partially meshed Frame Relay networks. Most protocols assume transitivity on a logical network; that is, if station A can talk to station B, and station B can talk to station C, then station A should be able to talk to station C directly. This is true on LANs, but is not true on Frame Relay networks unless A is directly connected to C. Additionally, certain protocols such as AppleTalk and transparent bridging could not be supported on partially meshed networks because they require "split horizon," in which a packet received on an interface cannot be transmitted out the same interface even if the packet is received and transmitted on different virtual circuits. By configuring Frame Relay subinterfaces, a single physical interface is treated as multiple virtual interfaces. This allows us to overcome split horizon rules. Packets received on one virtual interface can now be forwarded out another virtual interface, even if they are configured on the same physical interface.
Subinterfaces address these limitations by providing a way to subdivide a partially meshed Frame Relay network into a number of smaller, fully meshed (or point-to-point) subnetworks. Each subnetwork is assigned its own network number and appears to the protocols as if it is reachable through a separate interface. (Note that point-to-point subinterfaces can be unnumbered for use with IP, reducing the addressing burden that might otherwise result.)
For example, suppose you have a five-node Frame Relay network (see Figure 9-2) that is partially meshed (Network A). If the entire network is viewed as a single subnetwork (with a single network number assigned), most protocols assume that node A can transmit a packet directly to node E, when in fact it must be relayed through nodes C and D. This can be made to work with certain protocols (for example, IP) but will not work at all with other protocols (for example, AppleTalk) because nodes C and D will not relay the packet out the same interface on which it was received. One way to make this work fully is to create a fully meshed network (Network B), but that requires a large number of PVCs, which may not be economically feasible.
Using subinterfaces, the Frame Relay network can be subdivided into three smaller networks (Network C) with separate network numbers. Nodes A, B, and C are connected to a fully meshed network, and nodes C and D, as well as nodes D and E are connected via point-to-point networks. In this configuration, nodes C and D would see two subinterfaces, allowing them to forward packets without violating split horizon rules. I
To configure subinterfaces on a Frame Relay network, perform the following tasks:
| Task | Command |
|---|---|
| Step 1 Specify a serial interface. | interface serial number1 |
| Step 2 Configure Frame Relay encapsulation on the serial interface. | encapsulation frame-relay |
| Step 3 Specify a subinterface. | interface serial number.subinterface-number [multipoint | point-to-point]1. |
Subinterfaces can be configured for multipoint or point-to-point communication. Multipoint is the default.
For point-to-point subinterfaces, the destination is presumed to be known and is identified or implied in the frame-relay interface-dlci command. For multipoint subinterfaces, the destinations can be dynamically resolved through the use of Frame Relay Inverse ARP or can be statically mapped through the use of the frame-relay map command.
If you specified a point-to-point subinterface in Step 3 (above), perform the following task in interface configuration mode:
| Task | Command |
|---|---|
| Associate the selected point-to-point subinterface with a DLCI. | frame-relay interface-dlci dlci [option] |
For an explanation of the many available options, refer to this command in the Router Products Command Reference publication. For an example of how to associate a DLCI with a subinterface, see the section "Subinterface Examples" later in this chapter.
If you define a subinterface for point-to-point communication, you cannot reassign the same subinterface number to be used for multipoint communication without first rebooting the router. Instead, you can simply avoid using that subinterface number and use a different subinterface number instead.
If you specified a multipoint subinterface in Step 3 (above), perform the tasks in one or both of the following sections:
You can configure some protocols for dynamic address mapping and others for static address mapping.
Dynamic address mapping uses Frame Relay Inverse ARP to request the next-hop protocol address for a specific connection, given a DLCI. Responses to Inverse ARP requests are entered in an address-to-DLCI mapping table on the router; the table is then used to supply the next-hop protocol address or the DLCI for outgoing traffic.
Since the physical interface is now configured as multiple subinterfaces, you must provide information that distinguishes a subinterface from the physical interface and associates a specific subinterface with a specific DLCI.
To associate a specific multipoint subinterface with a specific DLCI, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
| Associate a specified multipoint subinterface with a DLCI. | frame-relay interface-dlci dlci |
Inverse ARP is enabled by default for all protocols it supports, but can be disabled for specific protocol-DLCI pairs. As a result, you can use dynamic mapping for some protocols and static mapping for other protocols on the same DLCI. You can explicitly disable Inverse ARP for a protocol-DLCI pair if you know the protocol is not supported on the other end of the connection. See the "Disable or Reenable Frame Relay Inverse ARP" section later in this chapter for more information.
Because Inverse ARP is enabled by default for all protocols that it supports, no additional command is required to configure dynamic address mapping on a subinterface.
For an example of configuring Frame Relay multipoint subinterfaces with dynamic address mapping, see the " " section.
A static map links a specified next-hop protocol address to a specified DLCI. Static mapping removes the need for Inverse ARP requests; when you supply a static map, Inverse ARP is automatically disabled for the specified protocol on the specified DLCI.
You must use static mapping if the router at the other end either does not support Inverse ARP at all or does not support Inverse ARP for a specific protocol that you want to use over Frame Relay.
To establish static mapping according to your network needs, perform one of the following tasks in interface configuration mode:
The supported protocols and the corresponding keywords to enable them are as follows:
The broadcast keyword is required for routing protocols such as OSI protocols and the Open Shortest Path First (OSPF) protocol. See the frame-relay map description in the Router Products Command Reference publication and the examples at the end of this chapter for more information about using the broadcast keyword.
For an example of how to establish static address mapping, see the sections "Two Access Servers in Static Mode Example," and "IPX Packet Access Server Example" later in this chapter.
Both point-to-point and multipoint Frame Relay subinterfaces can be configured with a backup interface. This allows individual PVCs to be backed up in case of failure rather than depending on the entire Frame Relay connection to fail before the backup takes over. You can configure a subinterface for backup on failure only, not for backup based on loading of the line.
If the serial interface has a backup interface, it will have precedence over the subinterface's backup interface in the case of complete loss of connectivity with the Frame Relay network. As a result, a subinterface backup is activated only if the serial interface is up, or if the serial interface is down and does not have a backup interface defined. If a subinterface has failed while its backup is in use, and then the serial interface goes down, the subinterface backup stays connected.
To configure a backup interface for a Frame Relay subinterface, perform the following tasks, beginning in global configuration mode:
| Task | Command |
|---|---|
| Step 1 Specify the interface. | interface serial number1 |
| Step 2 Configure Frame Relay encapsulation. | encapsulation frame-relay |
| Step 3 Configure the subinterface. | interface serial number.subinterface-number point-to-point1. |
| Step 4 Specify a DLCI for the subinterface. | frame-relay interface-dlci dlci |
| Step 5 Specify a backup interface for the subinterface. | backup interface serial number1. |
| Step 6 Specify backup enable and disable delay. | backup delay enable-delay disable-delay1. |
Frame Relay switching is a means of switching packets based upon the DLCI, which can be looked upon as the Frame Relay equivalent of a MAC address. The switching is performed by configuring your access server as a Frame Relay network. There are two parts to a Frame Relay network: a Frame Relay DTE (the access server) and a Frame Relay DCE switch. Figure 9-3 illustrates this concept.
In Figure 9-3, access servers A, B, and C are Frame Relay DTEs connected to each other via a Frame Relay network. Our implementation of Frame Relay switching allows our access servers to be used as depicted in this Frame Relay network.
Perform the tasks in the following sections, as necessary, to configure Frame Relay switching:
These tasks are described in the following sections.
You must enable packet switching before you can configure it on a Frame Relay DTE, DCE, or with Network to Network Interface (NNI) support. Do so by performing the following task in global configuration mode before configuring the switch type:
| Task | Command |
|---|---|
| Enable Frame Relay switching. | frame-relay switching |
For an example of how to enable Frame Relay switching, see the switching examples later in this chapter.
You can configure an interface as a DTE device, DCE switch, or as a switch connected to a switch to support NNI connections. (DCE is the default.) To do so, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
| Configure a Frame Relay DTE device or DCE switch. | frame-relay intf-type [dce | dte | nni] |
For an example of how to configure a DTE device or DCE switch, see the section "Hybrid DTE/DCE PVC Switching Example" later in this chapter.
For an example of how to configure NNI support, see the section "Pure Frame Relay DCE Example" later in this chapter.
You must specify a static route for PVC switching. To do so, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
| Specify a static route for PVC switching. | frame-relay route in-dlci out-interface out-dlci |
For an example of how to specify a static route, see the section "Pure Frame Relay DCE Example" later in this chapter.
Frame Relay Inverse ARP is a method of building dynamic address mappings in Frame Relay networks running AppleTalk, Banyan VINES, DECnet, IP, Novell IPX, and XNS. Inverse ARP allows the access server to discover the protocol address of a device associated with the virtual circuit.
Inverse ARP creates dynamic address mappings, as contrasted with the frame-relay map command, which defines static mappings between a specific protocol address and a specific DLCI (see the section "Configure Dynamic or Static Address Mapping" earlier in this chapter for more information).
Inverse ARP is enabled by default but can be disabled explicitly for a given protocol and DLCI pair. Disable or reenable Inverse ARP in the following conditions:
You do not need to enable or disable Inverse ARP if you have a point-to-point interface, because there is only a single destination and discovery is not required.
To select Inverse ARP, perform the following task in interface configuration mode:
Very large Frame Relay networks might have performance problems when a great many DLCIs terminate in a single access server and the access server must replicate access serving updates and service advertising updates on each DLCI. The updates can consume access-link bandwidth and cause significant latency variations in user traffic; the updates can also consume interface buffers and lead to higher packet rate loss for both user data and access serving updates.
To avoid such problems, you can create a special broadcast queue for an interface. The broadcast queue is managed independently of the normal interface queue, has its own buffers, and has a configurable size and service rate.
A broadcast queue is given a maximum transmission rate (throughput) limit measured in both bytes per second and packets per second. The queue is serviced to ensure that no more than this maximum is provided. The broadcast queue has priority when transmitting at a rate below the configured maximum, and hence has a guaranteed minimum bandwidth allocation. The two transmission rate limits are intended to avoid flooding the interface with broadcasts. The actual transmission rate limit in any second is the first of the two rate limits that is reached.
To create a broadcast queue, complete the following task in interface configuration mode:
| Task | Command |
|---|---|
| Create a broadcast queue for an interface. | frame-relay broadcast-queue size byte-rate packet-rate |
You can configure payload compression on point-to-point or multipoint interfaces or subinterfaces. Payload compression uses the stack method to predict what the next character in the frame will be. Because the prediction is done packet by packet, the dictionary is not conserved across packet boundaries.
Payload compression on each virtual circuit consumes approximately 40 KB for dictionary memory.
To configure payload compression on a specified multipoint interface or subinterface, complete the following task:
| Task | Command |
|---|---|
| Enable payload compression on a multipoint interface. | frame-relay map protocol protocol-address dlci payload-compress packet-by-packet |
To configure payload compression on a specified point-to-point interface or subinterface, complete the following task:
| Task | Command |
|---|---|
| Enable payload compression on a point-to-point interface. | frame-relay payload-compress packet-by-packet |
TCP/IP header compression, as described by RFC 1144, is designed to improve the efficiency of bandwidth utilization over low-speed serial links. A typical TCP/IP packet includes a 40-byte datagram header. Once a connection is established, the header information is redundant and need not be repeated in every packet that is sent. By reconstructing a smaller header that identifies the connection and indicates the fields that changed and the amount of change, fewer bytes can be transmitted. The average compressed header is 10 bytes long.
For this algorithm to function, packets must arrive in order. If packets arrive out of order, the reconstruction will appear to create regular TCP/IP packets but the packets will not match the original. Because priority queuing changes the order in which packets are transmitted, enabling priority queueing on the interface is not recommended.
You can configure TCP/IP header compression in either of two ways, as described in the following sections:
The "Disable TCP/IP Header Compression" section describes how to disable this feature.
TCP/IP header compression requires Cisco encapsulation. If you need to have IETF encapsulation on an interface as a whole, you can still configure a specific IP map to use Cisco encapsulation and TCP header compression.
In addition, even if you configure the interface to perform TCP/IP header compression, you can still configure a specific IP map not to compress TCP/IP headers.
You can specify whether TCP/IP header compression is active or passive. Active compression subjects every outgoing packet to TCP/IP header compression. Passive compression subjects an outgoing TCP/IP packet to header compression only if the packet had a compressed TCP/IP header when it was received.
To configure an IP map to use Cisco encapsulation and TCP/IP header compression, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
| Configure an IP map to use Cisco encapsulation and TCP/IP header compression. | frame-relay map ip-address dlci [broadcast] cisco tcp header-compression {active | passive} |
The default encapsulation is cisco.
For an example of how to configure TCP header compression on an IP map, see the "TCP Header Compression Examples" section later in this chapter.
You can configure the interface with active or passive TCP/IP header compression. Active compression, the default, subjects all outgoing TCP/IP packets to header compression. Passive compression subjects an outgoing packet to header compression only if the packet had a compressed TCP/IP header when it was received on that interface.
To apply TCP/IP header compression to an interface, you must perform the following tasks in interface configuration mode:
| Task | Command |
|---|---|
| Configure Cisco encapsulation on the interface. | encapsulation frame-relay |
| Enable TCP/IP header compression on the interface. | frame-relay ip tcp header-compression [passive] |
For an example of how to configure TCP header compression on an interface, see the "TCP Header Compression Examples" section later in this chapter.
You can disable TCP/IP header compression by using either of two commands that have different effects, depending on whether Frame Relay IP maps have been explicitly configured for TCP/IP header compression or have inherited their compression characteristics from the interface.
Frame Relay IP maps that have explicitly configured TCP/IP header compression must also have TCP/IP header compression explicitly disabled.
To disable TCP/IP header compression, perform one of the following tasks in interface configuration mode:
| Task | Command |
|---|---|
| Disable TCP header compression on all Frame Relay IP maps that are not explicitly configured for TCP header compression.
or Disable TCP header compression on a specified Frame Relay IP map. | no frame-relay ip tcp header-compression frame-relay map ip ip-address dlci nocompress
|
For an example of how to turn off TCP header compression, see the section "Turning Off TCP/IP Header Compression Examples."
You can specify which Frame Relay packets have low priority or low time sensitivity and will be the first to be dropped when a Frame Relay switch is congested. The mechanism that allows a Frame Relay switch to identify such packets is the discard eligibility (DE) bit.
This feature requires that the Frame Relay network be able to interpret the DE bit. Some networks take no action when the DE bit is set. Other networks use the DE bit to determine which packets to discard. The most desirable interpretation is to use the DE bit to determine which packets should be dropped first and also which packets have lower time sensitivity.
You can define DE lists that identify the characteristics of packets to be eligible for discarding, and you can also specify DE groups to identify the DLCI that is affected.
To define a DE list specifying the packets that can be dropped when the Frame Relay switch is congested, perform the following task in global configuration mode:
| Task | Command |
|---|---|
| Define a DE list. | frame-relay de-list list-number {protocol protocol | interface type number} characteristic |
You can specify DE lists based on the protocol or the interface, and on characteristics such as fragmentation of the packet, a specific TCP or UDP port, an access list number, or packet size. See the frame-relay de-list command for arguments and other information.
To define a DE group specifying the DE list and DLCI affected, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
| Define a DE group. | frame-relay de-group group-number dlci |
DLCI priority levels provide a traffic management tool for congestion problems caused by following situations:
DLCI priority levels provide a way to define multiple parallel DLCIs with different priorities for different types of traffic.
Before you configure the DLCI priority levels, complete the following tasks:
To configure DLCI priority levels, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
| Enable Frame Relay priority levels, associate specified DLCIs with the same group, and define their priority levels. | frame-relay priority-dlci-group group-number high-DLCI medium-DLCI normal-DLCI low-DLCI |
To monitor Frame Relay connections, perform any of the following tasks in EXEC mode:
| Task | Command |
|---|---|
| Clear dynamically created Frame Relay maps, which are created by the use of inverse ARP. | clear frame-relay-inarp |
| Display information about Frame Relay DLCIs and the LMI. | show interfaces serial number1 |
| Display LMI statistics. | show frame-relay lmi [type number] |
| Display the current Frame Relay map entries. | show frame-relay map |
| Display PVC statistics. | show frame-relay pvc [type number [dlci]] |
| Display configured static routes. | show frame-relay route |
| Display Frame Relay traffic statistics. | show frame-relay traffic |
This section provides examples of Frame Relay configurations. It includes the following examples:
The first example that follows sets IETF encapsulation at the interface level. The second example sets IETF encapsulation on a per-DLCI basis. In the first example, the keyword ietf sets the default encapsulation method for all maps to IETF.
encapsulation frame-relay IETFframe-relay map ip 172.30.123.2 48 broadcastframe-relay map ip 172.30.123.3 49 broadcast
In the following example, IETF encapsulation is configured on a per-DLCI basis. This configuration has the same result as the configuration in the first example.
encapsulation frame-relay frame-relay map ip172.30.123.2 48 broadcast ietf frame-relay map ip172.30.123.3 49 broadcast ietf
The following sections provide examples of static address mapping for the IP, AppleTalk, and IPX protocols.
The following examples illustrate how to configure two access servers for static mode.
interface serial 0 ! ip address172.30.64.2 255.255.255.0 encapsulation frame-relay keepalive 10 frame-relay map ip172.30.64.1 43
interface serial 0 ! ip address172.30.64.1 255.255.255.0 encapsulation frame-relay keepalive 10 frame-relay map ip172.30.64.2 44
The following example illustrates how to configure two access servers to communicate with each other using AppleTalk over a Frame Relay network. Each access server has a Frame Relay static address map for the other access server. The use of the appletalk cable-range command indicates that this is extended AppleTalk (Phase II).
! interface Serial0 ip address 172.21.59.24 255.255.255.0 encapsulation frame-relay appletalk cable-range 10-20 18.47 appletalk zone eng frame-relay map appletalk 18.225 100 broadcast
! interface Serial2/3 ip address 172.21.177.18 255.255.255.0 encapsulation frame-relay appletalk cable-range 10-20 18.225 appletalk zone eng clockrate 2000000 frame-relay map appletalk 18.47 100 broadcast !
The following example illustrates how to send packets destined for IPX address 200.0000.0c00.7b21 out on DLCI 102:
interface ethernet 0 ipx network 2abc ! interface serial 0 ipx network 200 encapsulation frame-relay frame-relay map ipx 200.0000.0c00.7b21 102 broadcast
The following sections provide basic Frame Relay subinterface examples and variations appropriate for different routed protocols and for bridging.
In the following example, subinterface 1 models a point-to-point subnet and subinterface 2 models a broadcast subnet. For emphasis, the multipoint keyword is used for serial subinterface 2, even though a subinterface is multipoint by default.
interface serial 0 encapsulation frame-relay interface serial 0.1 point-to-point ip address 10.0.1.1 255.255.255.0 frame-relay interface-dlci 42 interface serial 0.2 multipoint ip address 10.0.2.1 255.255.255.0 frame-relay map 10.0.2.2 18
The following example configures a serial interface for Frame Relay encapsulation and sets up multiple IPX virtual networks corresponding to Frame Relay subinterfaces:
ipx access server 0000.0c02.5f4f ! interface serial 0 encapsulation frame-relay interface serial 0.1 multipoint ipx network 1 frame-relay map ipx 1.000.0c07.d530 200 broadcast ipx network 2 frame-relay map ipx 2.000.0c07.d530 300 broadcast
For subinterface serial 0.1, the access server at the other end might be configured as follows:
ipx access server interface serial 2 multipoint ipx network 1 frame-relay map ipx 1.000.0c02.5f4f 200 broadcast
The following example sets up unnumbered IP over subinterfaces at both ends of a point-to-point connection. In this example, Access Server A functions as the DTE, and Access Server B functions as the DCE. Access Servers A and B are both attached to Token Ring networks.
frame-relay switching ! interface token-ring 0 ip address 172.30.177.1 255.255.255.0 ! interface serial 0 no ip address encapsulation frame-relay IETF ! interface Serial0.2 point-to-point ip unnumbered TokenRing0 ip pim sparse-mode frame-relay interface-dlci 20
frame-relay switching ! interface token-ring 0 ip address 172.30.178.1 255.255.255.0 ! interface serial 0 no ip address encapsulation frame-relay IETF bandwidth 384 clockrate 4000000 frame-relay intf-type dce ! interface serial 0.2 point-to-point ip unnumbered TokenRing1 ip pim sparse-mode bandwidth 384 frame-relay interface-dlci 20
The following configuration provides backward compatibility and interoperability. Creating this configuration is possible because of the flexibility provided by separately defining each map entry.
encapsulation frame-relay frame-relay map ip172.30.123.2 48 broadcast ietf ! interoperability is provided by IETF encapsulation frame-relay map ip172.30.123.3 49 broadcast ietf frame-relay map ip172.30.123.7 58 broadcast ! this line allows the access server to connect with a ! device running an older version of software frame-relay map DECNET 21.7 49 broadcast
Configure IETF based on map entries and protocol for more flexibility. Use this method of configuration for backward compatibility and interoperability.
When booting from a network server (netbooting) over Frame Relay, you cannot netboot via a broadcast. You must netboot from a specific host. Also, a frame-relay map command must exist for the host providing the netboot.
For example, if file igs3-bfx is to be booted from a host with IP address 172.30.126.2, the following commands need to be in the configuration:
boot systemigs3-bfx 172.30.126.2 interface Serial 0 encapsulation frame-relay frame-relay map IP172.30.126.2 100 broadcast
The frame-relay map command is used to map an IP address into a DLCI address. In order to netboot over Frame Relay, the address of the machine providing the netboot must be given explicitly, and a frame-relay map entry must exist for that site. For example:
boot systemigs3-bfx.83-2.0172.30.13.111 ! interface Serial 1 ip address172.30.126.200 255.255.255.0 encapsulation frame-relay ! frame-relay map IP172.30.126.111 100 broadcast
In this case, 100 is the DLCI of the remote access server that can get to host 172.30.126.111.
The remote access server must have the following frame-relay map entry:
frame-relay map IP 172.30.126.200 101 broadcast
This entry allows the remote access server to return a boot image (from the netboot host) to the access server netbooting over Frame Relay. Here, 101 is the DLCI of the access server being netbooted.
The following sections provide several examples of configuring one or more access servers as Frame Relay switches:
You can configure your access server as a dedicated, DCE-only Frame Relay switch. Switching is based on DLCIs. The incoming DLCI is examined, and the outgoing interface and DLCI are determined. Switching takes place when the incoming DLCI in the packet is replaced by the outgoing DLCI, and the packet is sent out the outgoing interface.
In the following example, the access server switches two PVCs between interface serial 1 and 2. Frames with DLCI 100 received on serial 1 will be transmitted with DLCI 200 on serial 2 (see Figure 9-4).
frame-relay switching ! interface Ethernet0 ip address 172.30.160.58 255.255.255.0 ! interface Serial1 no ip address encapsulation frame-relay keepalive 15 frame-relay lmi-type ansi frame-relay intf-type dce frame-relay route 100 interface Serial2 200 frame-relay route 101 interface Serial2 201 clockrate 2000000 ! interface Serial2 encapsulation frame-relay keepalive 15 frame-relay intf-type dce frame-relay route 200 interface Serial1 100 frame-relay route 201 interface Serial1 101 clockrate 64000
Using the PVC switching feature, it is possible to build an entire Frame Relay network using our access servers. In the following example, Access Server A and Access Server C act as Frame Relay switches implementing a two-node network. The standard Network to Network Interface (NNI) signaling protocol is used between Access Server A and Access Server C (see Figure 9-5).
frame-relay switching ! interface ethernet 0 no ip address shutdown ! interface ethernet 1 no ip address shutdown interface ethernet 2 no ip address shutdown ! interface ethernet 3 no ip address shutdown ! interface serial 0 ip address 172.30.178.48 255.255.255.0 shutdown ! interface serial 1 no ip address encapsulation frame-relay frame-relay intf-type dce frame-relay lmi-type ansi frame-relay route 100 interface serial 2 200 ! interface serial 2 no ip address encapsulation frame-relay frame-relay intf-type nni frame-relay lmi-type q933a frame-relay route 200 interface serial 1 100 clockrate 2048000 ! interface serial 3 no ip address shutdown
frame-relay switching ! interface ethernet 0 no ip address shutdown ! interface ethernet1 no ip address shutdown ! interface ethernet 2 no ip address shutdown ! interface ethernet 3 no ip address shutdown ! interface serial 0 ip address 172.30.187.84 255.255.255.0 shutdown ! interface serial 1 no ip address encapsulation frame-relay frame-relay intf-type dce frame-relay route 300 interface serial 2 200 ! interface serial 2 no ip address encapsulation frame-relay frame-relay intf-type nni frame-relay lmi-type q933a frame-relay route 200 interface serial 1 300 ! interface serial 3 no ip address shutdown
Access servers can also be configured as hybrid DTE/DCE Frame Relay switches (see Figure 9-6).
In the following example, Access Server B acts as a hybrid DTE/DCE Frame Relay switch. It can switch frames between the two DCE ports and between a DCE port and a DTE port. Traffic from the Frame Relay network can also be terminated locally. In the example, three PVCs are defined, as follows:
| Serial 1, DLCI 102 to serial 2, DLCI 201 | :DCE switching |
| Serial 1, DLCI 103 to serial 3, DLCI 301 | :DCE/DTE switching |
| Serial 2, DLCI 203 to serial 3, DLCI 302 | :DCE/DTE switching |
DLCI 400 is also defined for locally terminated traffic.
frame-relay switching ! interface ethernet 0 ip address 172.30.123.231 255.255.255.0 ! interface ethernet 1 ip address 172.30.5.231 255.255.255.0 ! interface serial 0 no ip address shutdown ! interface serial 1 no ip address encapsulation frame-relay frame-relay intf-type dce frame-relay route 102 interface serial 2 201 frame-relay route 103 interface serial 3 301 ! interface serial 2 no ip address encapsulation frame-relay frame-relay intf-type dce frame-relay route 201 interface serial 1 102 frame-relay route 203 interface serial 3 302 ! interface serial 3 ip address 172.30.111.231 encapsulation frame-relay frame-relay lmi-type ansi frame-relay route 301 interface serial 1 103 frame-relay route 302 interface serial 1 203 frame-relay map ip 172.30.111.4 400 broadcast
Switching over an IP tunnel is done by creating a point-to-point tunnel across the internetwork over which PVC switching can take place (see Figure 9-7).
The following configurations illustrate how to create the IP network depicted in Figure 9-7.
frame-relay switching ! interface Ethernet0 ip address172.30.123.231 255.255.255.0 ! interface Serial0 no ip address shutdown ip address172.30.222.231 255.255.255.0 encapsulation frame-relay frame-relay map ip172.30.222.4 400 broadcast frame-relay route 100 interface Tunnel1 200 ! interface Tunnel1 tunnel source Ethernet0 tunnel destination172.30.150.123
frame-relay switching ! interface Async0 ip address 172.30.231.123 255.255.255.0 encapsulation ppp ! interface Serial0 ip address 172.30.150.123 255.255.255.0 encapsulation ppp ! interface Tunnel1 tunnel source Async0 tunnel destination 172.30.123.231 ! interface Serial1 ip address 172.30.7.123 255.255.255.0 encapsulation frame-relay frame-relay intf-type dce frame-relay route 300 interface Tunnel1 200
These examples show various combinations of TCP/IP header compression and encapsulation characteristics on the interface and the effect on the inheritance of those characteristics on a Frame Relay IP map.
The following example shows an interface configured for TCP/IP header compression and an IP map that inherits the compression characteristics. Note that the Frame Relay IP map is not explicitly configured for header compression.
interface serial 1 encapsulation frame-relay ip address 172.30.177.178 255.255.255.0 frame-relay map ip 172.30.177.177 177 broadcast frame-relay ip tcp header-compression passive
Use of the show frame-relay map command will display the resulting compression and encapsulation characteristics; the IP map has inherited passive TCP/IP header compression:
access server> show frame-relay map
Serial 1 (administratively down): ip 172.30.177.177
dlci 177 (0xB1,0x2C10), static,
broadcast,
CISCO
TCP/IP Header Compression (inherited), passive (inherited)
This example also applies to dynamic mappings achieved with the use of inverse-arp on point-to-point subinterfaces where no Frame Relay maps are configured.
The following example shows the use of a Frame Relay IP map to override the compression set on the interface:
interface serial 1 encapsulation frame-relay ip address 172.30.177.178 255.255.255.0 frame-relay map ip 172.30.177.177 177 broadcast nocompress frame-relay ip tcp header-compression passive
Use of the show frame-relay map command will display the resulting compression and encapsulation characteristics; the IP map has not inherited TCP header compression:
Serial 1 (administratively down): ip 172.30.177.177
dlci 177 (0xB1,0x2C10), static,
broadcast,
CISCO
The following examples show the use of two different commands to turn off TCP/IP header compression.
In the first example, the initial configuration is the following:
interface serial 1 encapsulation frame-relay ip address 172.30.177.179 255.255.255.0 frame-relay ip tcp header-compression passive frame-relay map ip 172.30.177.177 177 broadcast frame-relay map ip 172.30.177.178 178 broadcast tcp header-compression
You enter the following commands interactively:
serial interface 1 no frame-relay ip tcp header-compression
As a result, header compression is turned off for the first map (with DLCI 177), which inherited its header compression characteristics from the interface, but not turned off for the second map (DLCI 178), which is explicitly configured for header compression.
In the second example, the initial configuration is the same, but you enter the following commands interactively:
serial interface 1 no frame-relay ip tcp header-compression frame-relay map ip 172.30.177.178 178 nocompress
The result of the interactive commands is to turn off header compression for the first map (with DLCI 177), which inherited its header compression characteristics from the interface, and also explicitly to turn off header compression for the second map (with DLCI 178), which had been explicitly configured for header compression.
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