Dial Ip Backup Connection for Primary Frame Relay Connection

Summary

In the following example the customer desires to have a Lucent PortMaster (Tm) router at the host site connect to another PortMaster router using a Frame Relay via synchronous ports. However, if that connection is interrupted  the remote router automatically dials the host router using a modem or an ISDN connection. Local Management Interface (LMI)  or Annex-D polling is used to determine when the Frame Relay link is down.

To set this up tell the remote router that its default gateway is the Ethernet IP address of the host router but with a high metric, like 4. The remote router must to listen for default routes on its Frame Relay interface. When one of the following three conditions occurs, the remote router will no longer have a default route via the Frame Relay interface. It  falls back to the default route with the higher metric, causing it to dial out to the host router using one of its serial ports. When the Frame Relay connection returns, the default route will be learned again using Routing Information Protocol (RIP); the backup connection (analog, ISDN) will eventually time out due to lack of traffic and hang up.

Configuration

NOTE: Similar configurations can be used for connections other than Frame Relay.

On the Remote Router:

  1. Configure the Ethernet interface 
    • Refer to Chapter 5 of the Configuration Guide for Lucent PortMaster (TM) Products, Configuring the Ethernet Interface
    • Refer to Ethernet Parameters from the Lucent PortMaster (TM)2 User Manual
    • Refer to Ethernet troubleshooting Guide 
  2. Configure global parameters (default gateway) 
    • Refer to Global Parameters from the PortMaster 2 User Guide
    • Refer to Configuration Guide for PortMaster Products

    IMPORTANT: The critical point to understand in making this possible is that the PortMaster does not update its routing table with learned dynamic routes which it has a static route for, EXCEPT for the default route. If the PortMaster learns a default route from RIP that has a better metric than its static default route, it will update its routing table with the "preferred" default route and "push down" the static default route.  The route is hidden but still available for future use should the dynamically learned default route disappear.

  3. Configure Frame Relay connection. 
  4. Configure a port for dial out (analog or ISDN) 
  5. Create a location to dial out on demand backup connection. 
    • Refer to Chapter 9 of the Configuration Guide for PortMaster Products, Configuring Dial Out Locations
    • See Managing the Location Table of the PortMaster 2 User Manual 

The three conditions that can trigger dial out are:

  1. If the CSU/DSU supports Data Carrier Detect (DCD), set it to drop DCD when the line goes away, and "set s1 modem on" on the IRX. When the CSU/DSU drops DCD the Lucent IRX router will reset the s1 port, bringing the Frame Relay interface down until DCD is asserted again by the CSU/DSU. When the interface is brought down the routes through it are marked invalid and the IRX will restore to the backup route. 
  2. If 6 LMI status packets in a row are not transmitted , the Frame Relay interface will be brought down until 6 LMI status packets in a row are received. The usual interval for LMI is 10 seconds, but this can be adjusted if the TelCo is willing. The TelCo and the setting on the IRX must agree on the LMI interval. (In 3.0R you can use LMI, in 3.2R you can use either Annex-D or LMI.) 
  3. If no RIP packets are seen via the Frame Relay interface for 3 minutes the routes will expire, and the static default route via the ISDN dial out will become active, triggering a dial out as soon as there is traffic for 1. 

On the Host Router:

  1. Configure the Ethernet interface 
    • Refer to Chapter 5 of the Configuration Guide for PortMaster Products, Configuring the Ethernet Interface
    • Refer to Ethernet Parameters of the PortMaster 2 User Manual
    • Refer to Ethernet Troubleshooting Guide 
  2. Configure global parameters (default gateway) 
  3. Refer to the Configure Frame Relay connection document. 
  4. Configure a port for dial in (analog or ISDN) 
    • Refer to the document Configuring PortMaster ports for network (Point to Point Protocol (PPP)/Serial Line Interface Protocol (SLIP) dial in 
  5. Create a netuser profile for dial in PPP user. 
    • Refer to Chapter 8 of the Configuration Guide for PortMaster Products, Configuring Dial In Users
    • Refer to Managing the Users Table from the PortMaster 2 User Manual

Example Configuration

IP Addresses: 

Host Site       ether0  192.168.1.1
                frm1    192.168.3.1
Remote Site     ether0  192.168.2.1
                frm1    192.168.3.2
Host Site               +------------+
                        | Gateway Router |------->Internet
                        +-------e0-------+
                  192.168.1.254/|
                                |
====ETHERNET=192.168.1.0/24==========
       |
       |/192.168.1.1 
+------e0------+
|     Host     |
|    Router    S0--[MODEM/TA]---+
+-----frm1-----+                |
       |\192.168.3.1            |
       |                        |
  FRAME RELAY                   |
  192.168.3.0/24                |
       |                        |
       |/192.168.3.2            |
+-----frm1-----+                |
|    Remote    |                |
|    Router    S0--[MODEM/TA]---+
+------e0------+
       |\192.168.2.1
       |
====ETHERNET=192.168.2.0/24==========
Remote Site

Note:  The synchronous ports on PortMaster routers ALWAYS require an external clock source.  The Telephone Company, the CSU/DSU or a Terminal Adapter (TA) must provide clocking to the PortMaster synchronous port.

On the remote router you have a similar configuration:

Command> set ether0 address 192.168.2.1
# Set the global settings 
Command> set gateway  192.168.1.1  4    
 # Set gateway 4 or higher

Command> set default listen

Note: Get the Frame Relay interface working before
setting up the backup link. Otherwise, the backup will
activate.

# Configure Frame Relay connection (Primary connection) 
Command> set s1 protocol frame
Command> set s1 address 192.168.3.2
Command> set s1 lmi 10
Command> set s1 routing broadcast


# If your CSU/DSU can assert carrier, "modem on" would be useful 
in this setup.
Command> set s1 modem off       

# Configure Dial out port (analog) S2 is used in the example.
Command> set s2 network dial out

Command> set s2 protocol ppp
Command> set s2 modem on
Command> set s2 xon/xoff off
Command> set s2 rts/cts on
Command> set s2 group 2
# Group number must match group number in location.

# Create on demand location to dial up back up connection to host router

Command> add location host_rtr
Command> set location host_rtr on_demand
Command> set location host_rtr address 192.168.1.1
Command> set location host_rtr netmask 255.255.255.0
# Netmask of host network

Command> set location host_rtr routing broadcast
Command> set location host_rtr protocol ppp
Command> set location host_rtr mtu 1500 
Command> set location host_rtr idletime 5 
# Drop connection after 5 minutes idle time 


Command> set location host_rtr maxports 1
Command> set location host_rtr group 2

# Replaced 5551212 with telephone number for remote router. 
Command> set location remote script 1 "atdt5551212" "=DCD="

Command> save all
Command> reset s1
Command> reset s2

On the host router you have a similar configuration. The host router MUST have a default gateway set for this setup to work.

# Configure Ethernet Interface
Command> set ether0 address 192.168.1.1

# Configure Global Settings
Command> set gateway 192.168.1.254
# IP address of next hop to 1 or upstream 

# Configure Frame Relay Connection
Command> set s1 protocol frame
Command> set s1 address 192.168.3.1
Command> set s1 lmi 10
Command> set s1 routing listen
Command> set s1 modem off

# Configure Serial port for dialin (analog) 
Command> set s2 network dialin
Command> set s2 protocol ppp
Command> set s2 modem on
Command> set s2 xon/xoff off
Command> set s2 rts/cts on
Command> set s2 idle 5 
# Drop connection after 5 minutes idle time 

# Configure user profile for dial in
Command> add netuser remote
Command> set user remote protocol ppp
Command> set user remote password xyzzy
Command> set user remote address 192.168.2.1    
# OR 255.255.255.255 to negotiate
Command> set user remote routing listen

# Save Configuration and reset ports. 
Command> save all
Command> reset s1
Command> reset s2