Router Installation and Configuration Manual/Configuring a Frame-Relay Interface

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This chapter describes how to configure the ImageStream router serial WAN interfaces for frame relay operation and includes the following topics:
  • Configuring a Frame Relay Master Interface
  • Default Frame Relay Interface Configuration
  • Customizing the Configuration
  • Setting Frame Relay Master Interface Parameters
  • Configuring a Frame Relay Subinterface
Before configuring the WAN interface, you must make the appropriate cabling connection for your needs. Refer to the hardware installation guide for your ImageStream product for information on making the WAN connection. See the Command Reference for more detailed command descriptions and instructions.

Contents

WAN Port Uses

WAN ports uses is explained in detail in Chapter 7, Router Installation and Configuration Manual/Configuring a Synchronous Serial WAN Interface and in Chapter 31, Router Installation and Configuration Manual/Basic Networking.

Understanding the Network Interface Configuration File

The wan.conf file is explained in detail in Chapter 5,Router Installation and Configuration Manual/Configuring a LAN Interface, and in Chapter 31, Router Installation and Configuration Manual/Basic Networking.

Configuring a Frame Relay Master Interface

Frame Relay is a standard communication protocol that is specified in CCITT recommendations I.122 and Q.922 which add relay and routing functions to the data link layer (layer 2 of the OSI reference model). Frames are constructed by encapsulating layer 2 messages (excluding the CRC and flags), with a two byte header, a CRC, and a flag delimiter. The frame relay header consists of a data link connection identifier (DLCI) that allows the network to route each frame on a hop-by-hop basis along a virtual path defined either at call setup or subscription time. The start and end flags, and the CRC are identical to those used by HDLC or SDLC based interfaced packages.
On an ImageStream router, each DLCI is defined on the physical frame relay interface as a subinterface. A subinterface is a logical (virtual) interface and is a part of a physical interface, such as a DS3. Each physical frame relay interface can be logically divided into as many as 4,092 different logical subinterfaces.
The frame relay port on each end of the connection must be configured prior to use. If your WAN interface has a synchronous serial interface, please see the Chapter 7, Router Installation and Configuration Manual/Configuring a Synchronous Serial WAN Interface prior to reading this chapter. If your WAN interface has an integrated CSU/DSU, please see Chapter 8, Router Installation and Configuration Manual/Configuring an Integrated CSU/DSU WAN Interface prior to reading this chapter.
This chapter assumes that the default configurations for your serial or integrated CSU/DSU WAN interface have already been completed. Only basic general commands will be covered in this chapter.
     Configuration menu 
     1. AAA (Password) Configuration 
     2. Global configuration 
     3. Network interface configuration 
     4. Firewall and QOS configuration 
     5. Service configuration 
     6. Dynamic routing configuration 
     7. Save configuration to flash 
     0. ISis-Router main menu 
From the "Configuration menu", select menu option 2, Network interface configuration, and press Enter. This will open the ImageStream router's primary configuration file, wan.conf, in the default editor. The wan.conf file is also accessible from the command line in the /usr/local/sand directory.

Default Frame Relay Interface Configuration

The default values of cards that will be using frame relay encapsulation match the default card configurations of the synchronous serial or integrated CSU/DSU interface cards which are explained in Chapter 7, Router Installation and Configuration Manual/Configuring a Synchronous Serial WAN Interface and in Chapter 8, Router Installation and Configuration Manual/Configuring an Integrated CSU/DSU WAN Interface. Remember that default settings are not necessarily shown in the configuration file.

Customizing the Configuration

To customize the WAN port configurations, complete the following sections. The ordering of the commands is done by convention, but a specific order is not required. Likewise, all configurations are indented to make configurations easy to read, but indentation is not required. In general, ImageStream follows this ordering convention:
  1. Comments
  2. Port description
  3. Bandwidth scaling statement
  4. Other optional settings
  5. IP address/netmask
  6. Secondary IP addresses/netmasks
  7. Subinterface configurations

Setting the Port Description

You can assign description to all WAN ports. Although this feature is optional, it may be particularly useful to assign names to facilitate administration. Setting a description does not change the operation or name of the port.
To assign a description to a port, enter this command in the wan.conf file in the serial interface configuration section:
     description string 
Using the the example configuration below, we have modified the description for Serial0:
     ! 
     interface Serial0 
     shutdown 
     description Frame relay connection to New York encapsulation hdlc 
     ip address 192.168.10.1 255.255.255.252 
     !

Setting the IP Address and Netmask

The frame relay master interface does not contain IP addressing information. All IP addresses are contained in the subinterfaces (logical interfaces) configured on the master interface. Using the default configuration below, we have deleted the ip address line.
     ! 
     interface Serial0 
     shutdown 
     description Frame relay connection to New York encapsulation hdlc 
     ! 


Setting Serial Transport Encapsulation

The serial transport encapsulation must be set to frame relay for a frame relay interface. No other encapsulation type may be specified. The syntax of this command is:
     encapsulation frame-relay ietf

In the default configuration below, we have changed the encapsulation to IETF frame relay. This encapsulation type corresponds to "encapsulation frame-relay ietf" on a Cisco router. Including the ietf keyword on a Cisco router when connecting to an ImageStream router is important, since Cisco routers default to a non-standard frame relay implementation.
     ! 
     interface Serial0 
     shutdown 
     description Frame relay connection to New York 
     encapsulation frame-relay ietf 
     !

Enabling or Disabling a Serial Interface

To disable an interface, use the shutdown interface configuration command. Unlike other command line interfaces, the wan.conf file does not require a "no" version of a command to reverse the operation. Entering "no" followed by a command will be ignored by SAND.
By default, Serial0 is disabled in the default configuration below because the shutdown command has been entered. Disabling a master interface will also disable all subinterfaces configured on the master device.
     ! 
     interface Serial0 
     shutdown 
     description Frame relay connection to New York encapsulation frame-relay ietf 
     ! 
To enable Serial0 in the configuration, remove the shutdown command. Do not use "no shutdown", as this will be ignored by SAND. It is not necessary to enter "no" and a command to negate the command. Simply remove the command from the configuration file.

Adding Comments to a Serial Configuration

Comments may be added to the Serial configuration, or anywhere in the wan.conf file by inserting a line that begins with the # symbol. The contents of the line will be ignored by SAND. Comments may be used to place contact information, ticket numbers, circuit IDs or any other information into the wan.conf file. There are no limits on the number or length of comments that may be inserted.
     ! 
     interface Serial0 
     #NOC phone: 800-555-1212 - Our account #58935 
     description Frame relay connection to New York encapsulation frame-relay ietf 
     ! 

Scaling the Connection Speed Calculation

For some media, such as Ethernet and Token Ring, the bandwidth is fixed; for other media, such as serial lines, you can change the actual bandwidth by adjusting the hardware. For both classes of media, you can use the bandwidth configuration command to communicate the current bandwidth to the router's statistical output program and other programs. The bandwidth command sets an informational parameter only to communicate the current bandwidth to other programs.
The bandwidth command does not adjust the actual bandwidth of an interface. Ports with integrated CSU/DSU's automatically calculate the bandwidth value based on the number of time slots configured. The syntax of the bandwidth command is:
     bandwidth bits per second

In the example below, we have added a bandwidth equal to a full T1 line (less overhead) to the Serial0 interface. This value is calculated automatically, so this command is optional:
     ! 
     interface Serial0 
     #NOC phone: 800-555-1212 - Our account #58935 
     description Frame relay connection to New York encapsulation frame-relay ietf 
     bandwidth 1536000 
     !

Setting Frame Relay Master Interface Parameters

The frame-relay command is used to configure the master interface parameters for an interface running frame relay encapsulation. In most cases, the defaults provided on the card will match the network configuration. Check with your line provider to determine if your line settings differ from the default configuration. The configurations in the interface configuration must match in two places: on the router and on the frame relay switch. If these settings do not match, your serial interface will not function.

Configuring the Local Management Interface (LMI)

Frame relay LMI is a frame relay control protocol sent to the router from the frame relay switch at the service provider and is not exchanged between routers. The LMI type at one location does NOT have to match the LMI type at other locations Your line provider will provide an LMI type to use. The syntax of this command is:
     frame-relay lmi-type { ansi | cisco | ccitt | none }

The ansi, cisco, ccitt, or none keywords specifies the type of LMI to use on this interface. ANSI (also known as "Annex D" or "LMI") is the default and most common value. Using the none keyword will disable the use of LMI. Disabling LMI will turn off the status messages between the switch and the router, tying the frame relay protocol status to the physical hardware status. We have specified the default value in the configuration below.
     ! 
     #NOC phone: 800-555-1212 - Our account #58935 
     interface Serial0 
     description Frame relay connection to New York 
     encapsulation frame-relay ietf 
     bandwidth 1536000 
     frame-relay lmi-type ansi
     !

Configuring the LMI Interval

When LMI is enabled, the router will begin to send status enquiries to the frame relay switch. The switch will respond with a status message. By default, these LMI messages are sent every 10 seconds. Check with your frame relay provider before changing this value. Setting a value that does not match the switch may cause outages on your frame relay line. To explicitly configure the LMI interval, include the LMI interval statement in the interface configuration for the serial device:
     frame-relay interval seconds

In the default configuration below, we have specified the default c-bit framing:
     ! 
     #NOC phone: 800-555-1212 - Our account #58935 interface Serial0 
     description Frame relay connection to New York encapsulation frame-relay ietf 
     bandwidth 1536000 
     frame-relay lmi-type ansi 
     frame-relay interval 10 
     !

Configuring a Frame Relay Subinterface

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. Transitivity is true on LANs, but not on Frame Relay networks unless A is directly connected to C.
Additionally, certain protocols, such as AppleTalk and transparent bridging, cannot 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.
Configuring Frame Relay subinterfaces ensures that a single physical interface is treated as multiple virtual interfaces. This capability 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 the limitations of Frame Relay networks 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).

Adding a Frame Relay Subinterface to an Existing Configuration

Each virtual interface (frame relay Permanent Virtual Circuit, or PVC) is configured using a subinterface in the wan.conf file. Although the order of the devices in the file does not matter, ImageStream by convention keeps the interfaces in following order.
Frame relay subinterfaces are configured in the same manner as Serial0 in our example configuration. Add an additional interface command for each frame relay serial interface, separating each section with a ! symbol. The syntax of the interface command is:
     interface DeviceName.subinterface#

This command creates a frame relay subinterface under the specified interface name. A subinterface is treated as a separate interface dedicated for a frame relay PVC to a remote site. In the example below, "Serial0" indicates that the subinterface belongs to the physical Serial0 interface and "1" is the unique subinterface ID number. The subinterface ID number can be any unique value between zero and 4,096 and does not have to be in any particular order (i.e. it is not necessary to begin with 1 and sequentially progress with 2, 3, 4, etc.). To reduce confusion, ImageStream recommends sequential progression for identifying a subinterface with the same number as the DLCI used on that subinterface.
In the default example below, we have added a two frame relay subinterfaces. Note that we have set the encapsulation on the subinterfaces to match the master interface.
     ! 
     #NOC phone: 800-555-1212 - Our account #58935 interface Serial0 
     description Frame relay connection to New York
     encapsulation frame-relay ietf 
     bandwidth 1536000 
     frame-relay lmi-type ansi 
     frame-relay interval 10 
     ! 
     interface Serial0.1 
     description Connection to NYC office 
     encapsulation frame-relay ietf 
     ! 
     interface Serial0.2 
     description Connection to Dallas office 
     encapsulation frame-relay ietf 
     !

Configuring the DLCI for a Frame Relay Subinterface

The configuration above is not yet complete. Each subinterface must contain a unique identifier used to send traffic across the frame relay network. Frame relay networks are connection oriented. This command assigns a Data Link Connection Identifier (DLCI) number to the corresponding frame-relay subinterface. A DLCI is assigned by the local frame relay provider for every Permanent Virtual Circuit (PVC) connected to the router. DLCI numbers are NOT exchanged between routers. DLCI numbering at one frame relay site is mutually exclusive from DLCI numbering at another site. When you are using frame relay encapsulation on an interface, you must map each subinterface to a DLCI assigned by your frame relay line provider.
To configure a DLCI on a point-to-point frame relay subinterface, include the frame-relay interface-dlci statement in the subinterface configuration. The syntax of the frame-relay interface-dlci command is:

frame-relay interface-dlci { dlci }

For each subinterface, you must configure the DLCI identifier. Your line provider will assign a unique DLCI to each PVC. Using the default example above, we added frame-relay interface-dlci statements. These settings must match those used on the frame relay network by your line provider or the frame relay interface will not function correctly.
    ! 
    #NOC phone: 800-555-1212 - Our account #58935 interface Serial0 
    description Frame relay connection to New York encapsulation frame-relay ietf 
    bandwidth 1536000 
    frame-relay lmi-type ansi 
    frame-relay interval 10 
    ! 
    interface Serial0.1 
    description Connection to NYC office 
    encapsulation frame-relay ietf 
    frame-relay interface-dlci 16 
    ! 
    interface Serial0.2 
    description Connection to Dallas office 
    encapsulation frame-relay ietf 
    frame-relay interface-dlci 17 
    ! 

Enabling FRF.12 end-to-end fragmentation on a subinterface

FRF.12 fragmentation and interleaving is a method of breaking up large data packets into small fragments which can be interleaved with small voice packets. This reduces jitter on low bandwidth links.
FRF.12 end-to-end fragmentation is enabled using the frame-relay fragment command:

frame-relay fragment { fragment length }

Example:

 interface Serial0.2
  encapsulation frame-relay ietf
  frame-relay interface-dlci 17
  frame-relay fragment 384
 !

Setting the IP Address and Netmask

During the subinterface setup process, you will set the IP address and netmask for the subinterface. To change the IP address and netmask of the Serial subinterface, modify the ip address command. The syntax of this command is:
     ip address ipaddress netmask

Set the IP address to the address to be used by the frame relay subinterface of the router on your network. If you have divided your network into subnets, enter the subnet mask that identifies how your network addresses are divided between the network portion and the host portion.
Using the default configuration above, we set the Serial0.1 IP address to 25.0.0.1 with a netmask of 255.255.255.252. We also set Serial0.2 to use an IP address of 30.0.0.1 and a /30 subnet mask. Often, with numbered point-to-point Serial links, the netmask will be a /30 (a subnet with 2 valid addresses). You will need to substitute your address and netmask for your network.
     ! 
     #NOC phone: 800-555-1212 - Our account #58935 interface Serial0 
     description Frame relay connection to New York encapsulation frame-relay ietf 
     bandwidth 1536000 
     frame-relay lmi-type ansi 
     frame-relay interval 10 
     ! 
     interface Serial0.1 
     description Connection to NYC office 
     encapsulation frame-relay ietf 
     frame-relay interface-dlci 16 
     ip address 25.0.0.1 255.255.255.252 
     ! 
     interface Serial0.2 
     description Connection to Dallas office 
     encapsulation frame-relay ietf 
     frame-relay interface-dlci 17 
     ip address 30.0.0.1 255.255.255.252 
     ! 

Adding Secondary Serial Addresses

Although rarely necessary, depending on your network configuration, you may need to configure more than one address on a subinterface. This task is accomplished by adding the secondary keyword to the ip address line used previously. The secondary keyword is used for all addresses on a Serial device other than the primary address. Only one primary address can be configured on a Serial device. Configuring more than one primary address or leaving the secondary keyword off of a secondary address configuration will cause the last primary IP address to be used when the port is configured by SAND.
Using the default configuration below, we have added two secondary IP addresses to Serial0.1. Only a portion of the previous configuration is shown.
     ! 
     interface Serial0.1 
     description Connection to NYC office 
     encapsulation frame-relay ietf 
     frame-relay interface-dlci 16 
     ip address 25.0.0.1 255.255.255.252 
     ip address 20.0.1.1 255.255.255.0 secondary 
     ! 
Note: You must save the settings to the router's non-volatile flash memory! If the router is rebooted before saving, your changes will be lost! See the Chapter 26, Router Installation and Configuration Manual/Backup/Restore Menu: Managing Configurations for more information.
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