15-37
Cisco ONS 15454 DWDM Reference Manual, R8.5
78-18343-02
Chapter 15 Management Network Connectivity
15.4 DCN Extension
ip route 10.0.0.0 255.0.0.0 192.168.20.1
ip route 10.0.0.0 255.0.0.0 Tunnel0 10
ip route 192.168.100.1 255.255.255.255 192.168.100.79
ip route 192.168.100.80 255.255.255.255 Tunnel0 10
Note that the host routing path to the peer DCN router (Router, IP 192.168.100.1) points to the
ONS 15454 network (by 192.168.200.79). This is required to set up the GRE tunnel. In this
configuration, only the external route to 10.0.0.0 (that include the NOC network) is overloaded with the
alternate path. However, overloading the last-resort route is also possible.
Table 15-8 shows network settings on the four ONS 15454 nodes. The static routes are created so the
DCN-connected nodes can advertise their capability to act as last-resort routers.
15.3.7.2 DCN Case Study 4 Limitations
Many limitations described in the “15.3.4.2 DCN Case Study 1 Limitations” section on page 15-27 also
apply to this case study. However, the problems are less acute because of the DCN connection in the
middle of the optical network. For DWDM networks, increased latency might became a problem if the
linear topology has many spans with intermediate line amplifier or optical add/drop multiplexing
(OADM) nodes, which is sometimes done to cover long-distance connections. In this case, when one
DCN fails, management packets for nodes near the middle of the span travel 1.5 times the complete
point-to-point connection. The normal routing figure is 0.5. The full connection length of a GRE tunnel
is used as an alternate routing path.
15.4 DCN Extension
ONS 15454 DWDM networks require a communication channel to exchange data among the different
nodes within the network. Until Software Release 7.0, the only usable channel was the optical service
channel (OSC) provided by the OSCM and OSC-CSM cards. In a long DWDM metro network, usage of
OSC channel adds limitations in terms of cost and performance because the OSC channel maximum loss
is 37 dB.
The primary aim of the DCN extension feature is to remove the OSC constraint and leverage on already
available external DCN or traffic matrix that allows nodes to be reached without using an OSC channel.
You can connect two nodes in a DWDM network without using an OSC channel in the following two
methods:
• Using external DCN
• Using GCC/DCC
Table 15-8 DCN Case Study 4 Node IP Addresses
Node IP Address/Mask Default Gateway
Static Routes:
Destination/Mask – Next Hop
Node 1 192.168.100.80/24 192.168.100.1 0.0.0.0/0 – 192.168.100.1
192.168.100.1/32 – 192.168.100.80
Node 2 192.168.100.79/24 192.168.100.2 192.168.100.2/32 – 192.168.100.79
Node 3 192.168.100.78/24 192.168.100.2 0.0.0.0/0 – 192.168.100.2
Node 4 192.168.100.77/24 0.0.0.0 —
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