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Connecting to CDRouter through multiple routers


In some cases it may be necessary to include an additional router in the test setup. Common examples include DSL or DOCSIS testing environments where a DSLAM or CMTS device (respectively) is required to forward traffic from the DUT to CDRouter’s WAN interface. If the intermediate device is performing IP/IPv6 routing at Layer-3, CDRouter must be properly configured to use this device as a gateway to route traffic back to the DUT.

If the DUT relies on DHCP or DHCPv6 to obtain its IP address, the intermediate router will need to be configured as a DHCP Relay Agent with CDRouter’s WAN address wanIspIp and/or ipv6WanIspIp in order to forward DHCP requests to between the DUT and CDRouter. CDRouter automatically supports DHCP/DHCPv6 requests from Relay Agents and will perform the proper message formatting when assigning addresses to the DUT.

Test Setup

In the example test setup shown below, an additional router is used to route between CDRouter’s WAN interface and the DUT, which are on different IP subnets.

IPv4 Configuration

To configure CDRouter to work with this setup, additional testvars must be included in the CDRouter configuration file. The wanIspGateway testvar is paired with wanIspIp and wanIspMask to identify the subnet for CDRouter’s WAN interface. wanIspAssignGateway , wanIspAssignIp and wanIspAssignMask correspond to the DUT’s interface. The IPv4HopCount should be set to 2 in this case.

If the DUT is using DHCP to obtain its IP address from CDRouter, the intermediate router must be configured as a DHCP relay to forward the DUT’s DHCP requests to CDRouter’s wanIspIp address.

The intermediate router should also be configured to use CDRouter’s WAN interface as its default route so that LAN traffic forwarded by the DUT to CDRouter’s simulated servers (DNS, NTP, TR-069 ACS, Remote Host, etc.) will be routed correctly. Alternatively, the intermediate router can be configured with static routes for these simulated servers, using wanIspIp as the next-hop for each destination.

A sample CDRouter configuration based on the test setup above is provided here:

# -- Sample CDRouter IPv4 routed configuration

testvar  wanMode                    DHCP

testvar  wanIspIp         
testvar  wanIspGateway    
testvar  wanIspMask       

testvar  wanIspAssignIp   
testvar  wanIspAssignGateway
testvar  wanIspAssignMask 

testvar  IPv4HopCount               2

IPv6 Configuration

Similar testvars exist for IPv6 configurations:

For IPv6 configurations the intermediate router must send router advertisements on the downstream interface so that the DUT can obtain a default route.

In addition, the relay must be able to route traffic from CDRouter’s simulated servers to the DUT’s LAN subnet. The DUT’s LAN prefix may be statically configured or dynamically delegated by CDRouter’s DHCPv6 server.

# -- Sample CDRouter IPv6 routed configuration

testvar supportsIPv6                yes
testvar ipv6WanMode                 DHCP

testvar ipv6WanIspIp                3001:A::1
testvar ipv6WanIspGateway           3001:A::2
testvar ipv6WanIspPrefixLen         64

testvar ipv6WanIspAssignIp          3001:B::2

testvar IPv6HopCount                2

testvar dhcpv6WanEnablePD           yes
testvar dhcpv6WanAssignPrefix       3001:DDDD::
testvar dhcpv6WanAssignPrefixLen    48
testvar ipv6LanSubnetId             FF
testvar ipv6LanIp                   ::%eui64%


If CDRouter is unable to fully initialize the DUT in a routed test setup, you can have it run some basic network connectivity checks to verify the path between CDRouter’s LAN and WAN connections.

These checks are enabled by setting the healthCheckEnable testvar to “yes”. When the tests are run CDRouter will successively ping each known router hop along the path between its local interface and the DUT. A summary of the results are displayed at the end of the “start” test log.

# -- Enable connectivity health checks

testvar healthCheckEnable           yes