Configuration Guide: Juniper CX111 FOR J Series and Branch SRX Series Devices

Juniper SRX100, SRX210, SRX240 AND SRX650 Router Firewalls and CX111 Bridges

Introduction

Due to their ubiquitous presence, the use of third-generation (3G) wireless networks has become a common deployment option for both primary and backup connectivity. With the introduction of Juniper Networks® CX111 Cellular Broadband Data Bridge, Juniper offers a simple way to provide wireless connectivity as either a backup or primary connection for Juniper Networks J Series Services Routers and branch SRX Series Services Gateways products.

Scope

The purpose of this application note is to provide an overview that shows how to configure and deploy the CX111 as a primary or backup 3G WAN connectivity option for Juniper Networks SRX Series and J Series platforms.

Design Considerations

Supported Hardware

Software Requirements

Card Compatibility

As of the date of this writing, about 50 different USB and ExpressCard modems have been certified to work with the CX111. The following list of modems have been tested to be generally compatible with the Juniper CX111 3G Bridge product. It may not be practical for Juniper to test every firmware that gets released for each modem. It is the responsibility of the end-user to test the modem with the CX111 3G Bridge before rolling into production.

Card Activation

Before cards can be used, they need to be programmed with the subscriber information required to access the service provider’s network. This is normally referred to as the card activation process. When service is purchased, the carrier will request the card’s ESN number, normally found printed on the wireless card. This number is then used for card identification by the different activation protocols.

Cards directly purchased from the wireless carrier can ship pre-activated, or sometimes they will ship with a companion software used to perform the initial activation. In either case, cards already activated do not have to be reactivated. Optionally, the cards can be activated from the CX111. This requires users to log into the CX111’s UI using a Web browser.

Description and Deployment Scenario

The CX111 ships with a default configuration that should accommodate most deployment scenarios. The deployment model assumes that the CX111 is connected to a DHCP-enabled interface.

The CX111 will maintain the wireless modem (or modems, if more than one modem is used) in a disconnected state, triggering a new connection as soon as the SRX Series/J Series requests a new lease. The modem(s) will be disconnected as soon as the lease expires, and only reconnected when that gateway requires another new lease.

When using the 3G link as the primary connection, long lease times can be used, as generally there won’t be a need to constantly connect and disconnect the line. On the other hand, if the CX111 is used to provide a backup connection, short lease times (in the order of a minute) are commonly used so that, when the primary link is active, the backup link can be disabled, triggering a disconnection, in the worse case, after a lease time.

The CX111 assigns the address received from the wireless service provider to the gateway (normally a public address). For obvious reasons, only a single device can be connected to the CX111 at any given time, or else multiple devices will contend for the only address passed to the CX111. The CX111 works in “pass through” mode, simply relaying all traffic from the wireless network to the DHCP client.

Management Interface

The CX111 provides a web-based management interface, and it can be accessed even when 3G modems are not used. Since “pass through” mode is used instead of a routed connection bridge that doesn’t do Network Address Translation (NAT), the management interface cannot be accessed through the normal data channel.

The management interface is still accessible through the Ethernet port, but VLAN tagging is used to separate management from data traffic using the following parameters

Management Network

Power over Ethernet

When available, Power over Ethernet (PoE) can be used to power the CX111. In the event that the CX111 is connected through a switch or a gateway that does not support PoE, an external power supply can be used (provided with the basic install kit). When PoE is used, the device will require about 3.5 watts of power per modem connected, so plan your power budget accordingly.

Dial Modes

The CX111 can be configured in two modes: “always on” or “dial on-demand.” In the “always on” mode, the CX111 connects to the 3G network after booting. The connection is always maintained, as long as there are no network or connectivity problems.

In “dial on-demand” mode, the CX111 only initiates a connection when it receives traffic from the interface connecting the CX111 and gateway. In particular, DHCP request messages will trigger a connection. Similarly, the connection will be dropped after a configurable inactivity timeout.

Regardless of the mode, the CX111 can accept multiple cards simultaneously. In the event of a failure or inability to connect, the remaining card(s) will be used. The connection priority is user configurable through the CX111’s management interface.

The default mode at shipping is ‘dial on-demand’ and set at 20 minutes idle timeout. Most carriers prefer the modem to disconnect if there is no interesting traffic. After the modem times out, the DHCP requests from the SRX Series device will result in a 192.168.30.x/24 response from the CX111. If interesting traffic is observed by the CX111, the modem re-dials. Modem connection takes about 15 to 20 seconds generally. After that, the next DHCP request from the SRX Series device will fetch the actual 3G IP address and internet connection is re-established.

Deployment Scenarios

In the following section, we will discuss several common deployment scenarios and provide the associated configurations.

CX111 Used for Primary Connectivity

This first scenario shows the gateway configuration when the 3G network is used as the primary WAN link. This can be achieved by simply connecting the CX111 to any interface in the untrust zone. On the SRX Series device, this is ge-0/0/0 when using the default configuration.

The relevant sections of the default configuration are shown here, for completeness.

set system services dhcp router 192.168.1.1
set system services dhcp pool 192.168.1.0/24 address-range low 192.168.1.2
set system services dhcp pool 192.168.1.0/24 address-range high 192.168.1.254
set system services dhcp propagate-settings ge-0/0/0.0
set interfaces interface-range interfaces-trust member ge-0/0/1
set interfaces interface-range interfaces-trust member fe-0/0/2
set interfaces interface-range interfaces-trust member fe-0/0/3
set interfaces interface-range interfaces-trust member fe-0/0/4
set interfaces interface-range interfaces-trust member fe-0/0/5
set interfaces interface-range interfaces-trust member fe-0/0/6
set interfaces interface-range interfaces-trust member fe-0/0/7
set interfaces interface-range interfaces-trust unit 0 family ethernet-switching vlan members vlan-trust
set interfaces ge-0/0/0 unit 0
set interfaces vlan unit 0 family inet address 192.168.1.1/24
set security nat source rule-set trust-to-untrust from zone trust
set security nat source rule-set trust-to-untrust to zone untrust
set security nat source rule-set trust-to-untrust rule source-nat-rule match source-address 0.0.0.0/0
set security nat source rule-set trust-to-untrust rule source-nat-rule then source-nat interface
set security zones security-zone trust host-inbound-traffic system-services all
set security zones security-zone trust host-inbound-traffic protocols all
set security zones security-zone trust interfaces vlan.0
set security zones security-zone untrust interfaces ge-0/0/0.0 host-inbound-traffic system-services dhcp
set security zones security-zone untrust interfaces ge-0/0/0.0 host-inbound-traffic system-services tftp
set security policies from-zone trust to-zone untrust policy trust-to-untrust match source-address any
set security policies from-zone trust to-zone untrust policy trust-to-untrust match destination-address any
set security policies from-zone trust to-zone untrust policy trust-to-untrust match application any
set security policies from-zone trust to-zone untrust policy trust-to-untrust then permit
set vlans vlan-trust vlan-id 3
set vlans vlan-trust l3-interface vlan.0

Enabling PoE

On SRX Series devices, it is possible to use PoE to power the CX111. The default configuration has PoE enabled on every PoE-capable interface, so users only have to connect the CX111 to a PoE-capable port. Enabling PoE only requires the addition of the following configuration.

/* The priority is optional but it will make sure that, if two many devices are being powered, the bridge will be given a high priority and will not be powered off */
set poe interface ge-0/0/0 priority high

Management Access

A VLAN-tagged logical interface can be used to provide access to the CX111’s management console. NAT can also be used to facilitate access from any device behind the gateway, eliminating the need for complex routing (as all traffic to the CX111’s management interface will be translated as if it originated from the management subnet).

/* The vlan.2 interface is the L3 interface of the data VLAN, connecting to the Bridge */
set system services dhcp propagate-settings vlan.2

/* Interface ge-0/0/0 has 2 VLANS configured, data and management */
set interfaces ge-0/0/0 description “Connection to CX111”
set interfaces ge-0/0/0 unit 0 family ethernet-switching port-mode trunk
set interfaces ge-0/0/0 unit 0 family ethernet-switching vlan members data
set interfaces ge-0/0/0 unit 0 family ethernet-switching vlan members management
set interfaces ge-0/0/0 unit 0 family ethernet-switching native-vlan-id data

/* vlan.0 connects to the untrust network */
set interfaces vlan unit 0 family inet address 192.168.1.1/24
/* vlan.2 connects to the bridge (untagged) */
set interfaces vlan unit 2 family inet dhcp client-identifier ascii SRX-GW
/* vlan.3900 connects to the bridge’s management subnet */
set interfaces vlan unit 3900 family inet address 192.168.0.2/24

/* VLANs */
set vlans data vlan-id 2
set vlans data l3-interface vlan.2
set vlans management vlan-id 3900
set vlans management l3-interface vlan.3900
set vlans vlan-trust vlan-id 3
set vlans vlan-trust l3-interface vlan.0

/* NAT rule for Internet access */
set security nat source rule-set trust-to-untrust from zone trust
set security nat source rule-set trust-to-untrust to zone untrust
set security nat source rule-set trust-to-untrust rule source-nat-rule match
source-address 0.0.0.0/0
set security nat source rule-set trust-to-untrust rule source-nat-rule then source-nat interface

/* NAT rule used for management access to the CX111*/
set security nat source rule-set trust-to-management from zone trust
set security nat source rule-set trust-to-management to zone management
set security nat source rule-set trust-to-management rule nat-to-CX111 match source-address 0.0.0.0/0
set security nat source rule-set trust-to-management rule nat-to-CX111 match destination-address 0.0.0.0/0
set security nat source rule-set trust-to-management rule nat-to-CX111 then source-nat interface

/* Security policies and zones */
set security zones security-zone trust host-inbound-traffic system-services all
set security zones security-zone trust host-inbound-traffic protocols all
set security zones security-zone trust interfaces vlan.0
set security zones security-zone untrust interfaces vlan.2 host-inbound-traffic system-services dhcp
set security zones security-zone untrust interfaces vlan.2 host-inbound-traffic system-services tftp
set security zones security-zone management interfaces vlan.3900
set security policies from-zone trust to-zone untrust policy trust-to-untrust match source-address any
set security policies from-zone trust to-zone untrust policy trust-to-untrust match destination-address any
set security policies from-zone trust to-zone untrust policy trust-to-untrust match application any
set security policies from-zone trust to-zone untrust policy trust-to-untrust then permit
set security policies from-zone trust to-zone management policy CX111-management-access match source-address any
set security policies from-zone trust to-zone management policy CX111-management-access match destination-address any
set security policies from-zone trust to-zone management policy CX111-management-access match application junos-http
set security policies from-zone trust to-zone management policy CX111-management-access match application junos-ping
set security policies from-zone trust to-zone management policy CX111-management-access then permit

CX111 Used for Backup

In this example, the CX111 will only be used when the primary interface is down. This is shown mostly for illustrative purposes, as only a failure in the primary interface will trigger a failover.

Also, this example can only be used with the CX111 operating in “always on” mode, as once connected, the DHCP requests from the SRX Series will keep the connection up. (Increasing the lease times is not a good idea, since there are no guarantees that, after a new connection, the modem will be assigned the same IP. Thus, this situation requires short lease times to make sure that the gateway is notified of the address change).

/* Interface Configs */
set interfaces interface-range Trust member-range fe-0/0/2 to fe-0/0/6
set interfaces interface-range Trust unit 0 family ethernet-switching port-mode access
set interfaces interface-range Trust unit 0 family ethernet-switching vlan members Trust

/* Main Internet Link */
set interfaces ge-0/0/0 unit 0 family inet address 198.0.0.2/24

/* CX111 backup link */
set interfaces ge-0/0/1 unit 0 family inet dhcp
set vlans default l3-interface vlan.1
set interfaces vlan unit 1 description Trust
set interfaces vlan unit 1 family inet address 192.168.1.1/24

/* Default route points to the primary link and it takes precedence over the DHCP assigned default */
set routing-options static route 0.0.0.0/0 next-hop 198.0.0.1

/* NAT Configuration */
set security nat source rule-set Outbound-NAT from zone trust
set security nat source rule-set Outbound-NAT to zone untrust
set security nat source rule-set Outbound-NAT rule Nat-All match source-address 0.0.0.0/0
set security nat source rule-set Outbound-NAT rule Nat-All match destination-address 0.0.0.0/0
set security nat source rule-set Outbound-NAT rule Nat-All then source-nat interface

/* Security Zones */
set security zones security-zone untrust interfaces ge-0/0/0.0 host-inbound-traffic system-services ping
set security zones security-zone untrust interfaces ge-0/0/1.0 host-inbound-traffic system-services dhcp
set security zones security-zone trust host-inbound-traffic system-services ping
set security zones security-zone trust interfaces vlan.1 host-inbound-traffic system-services dhcp
set security zones security-zone trust interfaces vlan.1 host-inbound-traffic system-services ping
set security zones security-zone trust interfaces vlan.1 host-inbound-traffic system-services ssh

/* Allow outboud traffic from trust to untrust */
set security policies from-zone trust to-zone untrust policy permit-outbound match source-address any
set security policies from-zone trust to-zone untrust policy permit-outbound match destination-address any
set security policies from-zone trust to-zone untrust policy permit-outbound match application any
set security policies from-zone trust to-zone untrust policy permit-outbound then permit

Detecting Network Failures Using RPM Probes

Although quite simple, our previous example presents a major drawback—the primary interface’s status is not always a good indicator of the network’s connectivity. In some instances, when layer 2 protocols are not able to detect end-to-end failures, or when multiple network hops separate the Juniper Networks SRX210 Services Gateway from remote resources, other means to trigger a failover are desired.

This example shows how to configure a set of watch prefixes which, when they are not present in the routing table, will enable the dialer interface. Static routes with Bidirectional Forwarding Detection (BFD) monitoring or routing protocols can be used to dynamically change the status of the routes in the routing table.

The main advantage of this approach is that real-time performance monitoring (RPM) probes do not require any special routing protocol support or the use of BFD. RPM probes can be configured to use standard Internet Control Message Protocol (ICMP) messages, HTTP get requests, or TCP/UDP pings to verify end-to-end connectivity.

Even though this example builds on the previous one, in order to present a complete working scenario, the full configuration is shown below.

/* Enable the commit script. The commit script must be stored under /var/db/scripts/commit */
set system scripts commit allow-transients
set system scripts commit file rpm-monitor-config.xslt
/* Enable the event script. The script file must be stored under /var/db/scripts/event */
set event-options event-script file rpm-monitor.xslt

/* Local dhcp server configuration */
/* This server assigns addresses to the hosts in the Trust network */
set system services dhcp pool 192.168.1.0/24 address-range low 192.168.1.2
set system services dhcp pool 192.168.1.0/24 address-range high 192.168.1.254
set system services dhcp pool 192.168.1.0/24 router 192.168.1.1

/* This configuration creates a log file named rpm-monitor containing the login messages from the script */
set system syslog file rpm-monitor user warning
set system syslog file rpm-monitor match cscript

/* Interface Configs */
set interfaces interface-range Trust member-range fe-0/0/2 to fe-0/0/6
set interfaces interface-range Trust unit 0 family ethernet-switching port-mode access
set interfaces interface-range Trust unit 0 family ethernet-switching vlan members Trust
set interfaces ge-0/0/0 unit 0 family inet address 198.0.0.2/24
set interfaces vlan description CX111-data
set interfaces vlan unit 1 description Trust
set interfaces vlan unit 1 family inet address 192.168.1.1/24
set vlans default l3-interface vlan.1

/* The backup interface should be normally disabled */
/* The monitoring scripts point to an RPM probe and, if the probe fails, the script will enable the backup interface */
set interfaces ge-0/0/1 unit 0 apply-macro rpm-monitor-server1 test-name server1
set interfaces ge-0/0/1 unit 0 apply-macro rpm-monitor-server1 test-owner rpm-monitor-probes
set interfaces ge-0/0/1 unit 0 disable
set interfaces ge-0/0/1 unit 0 family inet dhcp

/* RPM probe configuration */
/* Note that we are using the primary link address as the source so, when the backup link is enabled, the probes will still fail unless the primary link comes back up. This script pings destination ‘target’ address. Wait for 5’ ping failures and has a ‘5 second’ probe interval. After 5 pings, the test waits for 15seconds before starting the pings again.*/
set services rpm probe rpm-monitor-probes test server1 probe-type icmp-ping
set services rpm probe rpm-monitor-probes test server1 target address 96.17.23.148
set services rpm probe rpm-monitor-probes test server1 probe-count 5
set services rpm probe rpm-monitor-probes test server1 probe-interval 5
set services rpm probe rpm-monitor-probes test server1 test-interval 15
set services rpm probe rpm-monitor-probes test server1 source-address 10.0.1.20

/* Default route pointing to the primary link */
set routing-options static route 0.0.0.0/0 next-hop 198.0.0.1

/* NAT configuration */
set security nat source rule-set Outbound-NAT from zone trust
set security nat source rule-set Outbound-NAT to zone untrust
set security nat source rule-set Outbound-NAT rule Nat-All match source-address 0.0.0.0/0
set security nat source rule-set Outbound-NAT rule Nat-All match destination-address 0.0.0.0/0
set security nat source rule-set Outbound-NAT rule Nat-All then source-nat interface

/* Zones and policies */
set security zones security-zone untrust interfaces ge-0/0/0.0 host-inbound-traffic system-services ping
set security zones security-zone untrust interfaces ge-0/0/1.0 host-inbound-traffic system-services dhcp
set security zones security-zone trust host-inbound-traffic system-services ping
set security zones security-zone trust interfaces vlan.1 host-inbound-traffic system-services dhcp
set security zones security-zone trust interfaces vlan.1 host-inbound-traffic system-services ping
set security zones security-zone trust interfaces vlan.1 host-inbound-traffic system-services ssh
set security policies from-zone trust to-zone untrust policy permit-outbound match source-address any
set security policies from-zone trust to-zone untrust policy permit-outbound match destination-address any
set security policies from-zone trust to-zone untrust policy permit-outbound match application any
set security policies from-zone trust to-zone untrust policy permit-outbound then permit

Monitoring

The 3G signal strength and connection status can be monitored from the CX111’s management interface, which is found under status -> device info tab.

Traffic statistics can be found under the Status->Statistics page.

When using the RPM monitor scripts, it is quite useful to look at the script logs. These logs record events such as probe failures, enabling/disabling of the backup interface, etc. Using the configuration shown in the last example, the logs can be viewed with the “show log rpm-monitor” command.

# run show log rpm-monitor
Jan 22 05:15:48 SRX210-Home cscript: rpm-monitor: Triggered by ping_test_up test server1 owner rpm-monitor-probes
Jan 22 05:15:48 SRX210-Home cscript: rpm-monitor: RPM probe up flagged, but there is nothing to do with the logical interfaces
Jan 22 05:16:59 SRX210-Home cscript: rpm-monitor: Triggered by ping_test_up test server1 owner rpm-monitor-probes
Jan 22 05:16:59 SRX210-Home cscript: rpm-monitor: RPM probe up flagged, but there is nothing to do with the routes

The result of the RPM probes can be viewed with the following command:

pato@SRX210-Home# run show services rpm history-results
Owner, Test             Probe received             Round trip time
rpm-monitor-probes, server1 Fri Jan 22 05:29:40 2010 192057 usec
rpm-monitor-probes, server1 Fri Jan 22 05:29:45 2010 194821 usec
rpm-monitor-probes, server1 Fri Jan 22 05:29:50 2010 197966 usec
rpm-monitor-probes, server1 Fri Jan 22 05:29:55 2010 188755 usec
rpm-monitor-probes, server1 Fri Jan 22 05:30:00 2010 189775 usec
rpm-monitor-probes, server1 Fri Jan 22 05:30:16 2010 199006 usec
rpm-monitor-probes, server1 Fri Jan 22 05:30:21 2010 190135 usec
rpm-monitor-probes, server1 Fri Jan 22 05:30:26 2010 190896 usec
rpm-monitor-probes, server1 Fri Jan 22 05:30:31 2010 192937 usec
rpm-monitor-probes, server1 Fri Jan 22 05:30:36 2010 203084 usec

Summary

As more and more wireless carriers expand their coverage and upgrade their networks to offer 3G wireless data services, enterprises worldwide can look to use 3G as a backup connectivity solution for many deployments and in some cases, even use 3G wireless as primary data access.

Juniper Networks SRX Series Services Gateways provide world-class security and routing features, and now combined with the flexible and optimized CX111 Cellular Broadband Data Bridge, the SRX Series can offer additional WAN connectivity solutions to customers for increased WAN uptime coupled with reduced operational expense. The CX111 is simple to configure and deploy, which can be installed easily in existing and new SRX Series and J Series deployments.