Configuring Frame Relay Sub Interfaces (DLCI Bundling)

August 25, 1999

Summary:

Lucent PortMaster (TM) products support a feature called Data Link Connection Identifier (DLCI) 
Bundling which allows each synchronous interface to be configured for up to 33 Frame Relay networks; this includes the one primary interface and 32 sub interfaces. Each interface becomes an entry point to a separate Frame Relay network (cloud). 

The primary interface is configured normally as a frame relay interface. Each sub interface is created by adding a location to the PortMaster using frame as the protocol; this distinguishes the location as a sub interface. Each location is then configured with a group number to match that of the primary synchronous interface. Each location is  populated with DLCI numbers, among other configurations. 

Reasons to use  sub interface: 

  • If you have two Frame Relay networks to connect to:
    • One may want to configure the router to connect to an Internet provider or a central office using Frame Relay on the primary interface and then connect several branch offices using Frame Relay with a sub interface.

     

  • Limitation of DLCI numbers on the primary interface: 
    • Using static DLCI lists on the primary Frame Relay interface instead of LMI or Annex-d to discover the DLCI lists automatically limits the static DLCI list to 240 characters. If a larger number of static DLCI's are required a sub interface must be used to hold the large list of static DLCI's. 

Important Notes

  • You can have up to 32 (thirty-two) sub interfaces per synchronous port. 
  • Learning DLCIs from the Frame Relay switch (using LMI or Annex-d polling) works only on the primary interface and not on the sub interface. Which means with a sub interface you have to use static DLCI lists. 
  • Frame Relay sub interfaces  use only one protocol IP or IPX not both. 
  • Sub interfaces establish a few seconds after the primary interface.. 
  • Sub interfaces can only be configured from the command line interface. 

Creating The Sub Interface Location

  1. Create the location using a name of your choice. This name (or label) will be used to reference the location. 
    2. Command> add location [name_of_location]
  2. Give the sub interface location and the Wide Area Network (WAN) port (aka: synchronous port, primary interface) a common group number.
    • The common group number allows the PortMaster to know which sub interface goes with each primary interface.  It does not matter what group number you use as long as it is consistent between the port and the location. 
      • Command> set location [name_of_location] group [group number]
Command> set [primary port name] group [group number]

    Example:  

    Command> set location isp group 27
Command> set w1 group 27
  3. Set the protocol of the location to 'Frame'. This will designate the location as a Frame Relay sub interface. 
    4. Command> set location [name_of_location] protocol Frame
  4. Give the Frame Relay sub interface an IP address and netmask:
    • The IP address will be an IP address that is a member of the IP network being used by the Frame Relay network. This means that each router connected to the Frame Relay network needs to have a Frame Relay interface in the same IP network/subnet. 
    • The netmask will be the netmask of the Frame Relay network. Each router connected to this same Frame Relay network will also have this same netmask. 
      • Command> set location[name_of_location]address [IP address of
sub interface]

Command> set location[name_of_location]netmask [netmask of Frame-Relay
network]

     

  5. Set the Maximum Transfer Unit size. 
    6. Command> set location [name_of_location] mtu 1500
  6. Configure the sub interface for Routing Information Protocol (RIP) routing.
    • Generally, if the sub interface is on the router providing access it will be set to listen. 
    • If the sub interface is on the router receiving access it will be set to broadcast.
      • Command> set location [name_of_location] routing 
[on, off, broadcast, listen]
  7. Add DLCIs to Location: 
    • When using a sub interface you MUST use static DLCI lists. 
    • Learning DLCIs from the Frame Relay switch (using LMI or Annex-d polling) works only on the primary interface. 
    • The IP address of the remote WAN port is optional. 
      • Command> add dlci [name_of_location] [DLCI of PVC/Telco] 
[IP address of remote WAN port]

    NOTES: 

    • You can view the sub interface configuration with command> show location [name of location]
    • If the [IP address of remote WAN port] is left out  the PortMaster will try to learn that IP automatically with inverse arp. 
    • The keyword dlci is the same as the keyword ipdlci 
    • The keyword ipxdlci is used for IPX dlci lists (With Internet Packet eXchange (IPX) the WAN port can be referenced as a hex address or in dotted decimal notation). 
      • Command> add ipxdlci ispnet 21 10.11.12.13
This is the same as...
Command> add ipxdlci ispnet 21 0a0b0c0d
    • DLCI entries can be removed from the sub interface location with the delete keyword: 
      • Command> delete dlci [name_of_location]
[DLCI of PVC/Telco]
Command> delete ipxdlci [name_of_location]
[DLCI of PVC/Telco]

 Configuration Example:

Command> add location ispnet
Location ispnet successfully added


Command> set location ispnet group 27 
# setting group number
ispnet group number changed from 0 to 27


Command> set w1 group 27
Group number for port W1 changed from 0 to 27


Command> set location ispnet protocol Frame
ispnet protocol changed to Frame Relay


Command> set location ispnet address 192.168.1.1 
# setting IP address for sub interface  
ispnet destination changed from 0.0.0.0 to 192.168.1.1


Command> set location ispnet netmask 255.255.255.0
ispnet netmask changed from 0.0.0.0 to 255.255.255.0


Command> set location ispnet mtu 1500
ispnet mtu changed from 1500 to 1500


Command> set location ispnet routing listen
ispnet routing changed from off to no_broadcast,listen


Command> add dlci ispnet 16 192.186.1.2 
# Adding DLCI numbers to loc
New dlci successfully added


Command> add dlci ispnet 17 192.168.1.3
New DLCI successfully added


Command> save all            
# Saves the configuration


Saving global configuration
Saving ports
User table successfully saved
Hosts table successfully saved
Static route table successfully saved
Location table successfully saved
SNMP table successfully saved
Filter table successfully saved
New configurations successfully saved.
Command> reset w1
# Reset Primary interface for changes to take effect. 
Resetting port W1
 
# Configurations will look similar to the following example:
Command> show location ispnet
    Location: ispnet                   Type: Sub-Interface
  IP Address: 192.168.1.1           Netmask: 255.255.255.0
    Protocol: Frame Relay           Options: Listen, Compression
       Group: 27                        Mtu: 1500

 IP DLCI's:  DLCI   Address
             -----  ------------
             16     192.186.1.2
             17     192.168.1.3

Debugging Tools

  • Be aware that depending on how Frame Relay is configured on the primary and sub interfaces, it can take a few seconds or as long a few minutes for both the primary and sub interfaces to reach an ESTABLISHED state.
    • Primary interface comes up first. Static DLCI's are faster than learned DLCI's. 
    • Sub interface comes up after the primary interface. If IP addresses are configured in the location with their respective DLCI numbers there is a faster response.

     

  • Sub interface state: 
    • The ifconfig command shows all active interfaces and information about them. 
    • After resetting the primary interface you will see the primary interface become active first (using the ifconfig command). 
    • After the primary interface the second interface will come up. 
      • Command> ifconfig
  •  DLCI numbers associated with WAN ports: 
    • The PortMaster will not be able to communicate with a host on the other side of the Frame cloud unless the DLCI number in the Frame Relay switch is associated with an IP address. These IP address can be entered manually when configuring the sub interface (see above) or they can be learned via inverse arp. 
    • To show a list of DLCI numbers and corresponding IP addresses enter command show arp [interface name]. The 'show arp' expects the name  and interface information found when using the command ifconfig.
      • Command> show arp frm21

Troubleshooting

  1. Always reset the port (primary Frame Relay interface) after changing the primary or sub interface configurations, especially the DLCI lists. 
  2. Verify that  the primary and/or the sub interface have established themselves using command ifconfig.
    • Verify that the primary interface has a static DLCI list containing DLCI numbers being used by the sub interface. 
    • Verify that the port being used by the primary interface is showing 'Abort errors', 'CRC errors', or 'Framing Errors' all of which point to problems with the primary interface that must  be resolved before the sub interface can begin to work. 

     

  3. Verify that  the primary Frame Relay interface is working before troubleshooting the sub interface. See notes on configuring Frame Relay. 
  4. Verify the configuration of the sub interface. 
    • The most common error is putting a colon ":" between the DLCI number and the IP address of the remote WAN port. The primary interface configuration command worked in the past. Currently the add dlci command is used for both the primary and sub interfaces.  

      •  COLONS ARE NOT REQUIRED IN DLCI LIST FOR THE SUB INTERFACE. 

    • Verify the list of DLCIs tied to each location using the command  show location [location name]  

     

  5. Verify that each DLCI number is resolving to an IP address using the command show arp [interface name]. 
  6. Verify that the local IP address for the sub interface is in the same subnet or IP network as all other Frame Relay interfaces of the other routers and that all the netmasks match. 
  7. Verify that the group number for the location matches the group number on the primary interface exactly. 
  8. Verify that the protocol is set to 'Frame Relay' and the type reads 'Sub Interface' as shown in the example below. Use command show location [location name].
    9. Command> show location ispnet
    Location: ispnet                   Type: Sub-Interface
  IP Address: 192.168.1.1           Netmask: 255.255.255.0
    Protocol: Frame Relay           Options: Listen, Compression
       Group: 27                        Mtu: 1500

 IP DLCI's:  DLCI   Address
             -----  ------------
             16     192.186.1.2
             17     192.168.1.3