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Cisco ONS 15454 SDH Reference Manual, R5.0
April 2008
Chapter 12 CTC Network Connectivity
12.2.8 Scenario 8: Dual GNEs on a Subnet
If the packet is addressed to the ONS 15454 SDH, additional rules shown in Table 12-4 apply. Rejected
packets are silently discarded.
If you implement the proxy server, keep the following rules in mind:
• All DCC-connected ONS 15454 SDH nodes on the same Ethernet segment must have the same
Craft Access Only setting. Mixed values produce unpredictable results, and might leave some nodes
unreachable through the shared Ethernet segment.
• All DCC-connected ONS 15454 SDH nodes on the same Ethernet segment must have the same
Enable Firewall setting. Mixed values produce unpredictable results. Some nodes might become
unreachable.
• If you check Enable Firewall, always check Enable Proxy. If Enable Proxy is not checked, CTC
cannot see nodes on the DCC side of the ONS 15454 SDH.
• If Craft Access Only is checked, check Enable Proxy. If Enable Proxy is not checked, CTC cannot
see nodes on the DCC side of the ONS 15454 SDH.
If nodes become unreachable in cases 1, 2, and 3, you can correct the setting by performing one of the
following:
• Disconnect the craft computer from the unreachable ONS 15454 SDH. Connect to the
ONS 15454 SDH through another ONS 15454 SDH in the network that has a DCC connection to the
unreachable ONS 15454 SDH.
• Disconnect the Ethernet cable from the unreachable ONS 15454 SDH. Connect a CTC computer
directly to the ONS 15454 SDH.
12.2.8 Scenario 8: Dual GNEs on a Subnet
The ONS 15454 SDH provides GNE load balancing, which allows CTC to reach ENEs over multiple
GNEs without the ENEs being advertised over OSPF. This feature allows a network to quickly recover
from the loss of GNE, even if the GNE is on a different subnet. If a GNE fails, all connections through
that GNE fail. CTC disconnects from the failed GNE and from all ENEs for which the GNE was a proxy,
and then reconnects through the remaining GNEs. GNE load balancing reduces the dependency on the
launch GNE and DCC bandwidth, both of which enhance CTC performance. Figure 12-14 shows a
network with dual GNEs on the same subnet.
Table 12-4 Proxy Server Firewall Filtering Rules When Packet Addressed to ONS 15454 SDH
Packets Arriving At Accepts Rejects
TCC2/TCC2P
Ethernet interface
• All UDP packets except those in
the Rejected column
• UDP packets addressed to the
SNMP trap relay port (391)
DCC interface
• All UDP packets
• All TCP packets except those in
the Rejected column
• OSPF packets
• ICMP packets
• TCP packets addressed to the
Telnet port
• TCP packets addressed to the
proxy server port
• All packets other than UDP, TCP,
OSPF, and ICMP.