RuggedCom RuggedRouter RX1100 - Manual (Page 57)

5. Configuring Networking
Revision 1.14.3 57 RX1000/RX1100™
Figure 5.8. End To End Backup Example
The backup is “end to end” because connectivity is determined by the availability of an interface on the
target system, and not a local link. In the above figure, interface w1ppp acts as the primary interface
and eth1 acts as the secondary interface. The router tests the primary path by probing 192.168.16.2
on router 2. A failure of the either w1ppp, network A or the remote link on router2 will render the
primary path as “failed”.
If the primary path fails, the routing table will be modified to direct packets out the secondary (eth1
in the above figure).
Presumably, the secondary is a higher cost (and perhaps lower throughput) path. In the initial
deployment of this feature, the secondary path was implemented with Ethernet-CDMA modem. The
modem featured a low latency connection time (initiated by the reception of packets) but had a low
bandwidth capability and high monetary cost.
Note that the feature must be implemented at both routers. If the feature is only implemented at
router 1, the second router's gateway will still point towards Network A after a failure of the primary
path. Packets from router 1 would reach router 2 through the secondary, but the responses would
disappear in the black hole of the failed path.