Cisco ONS 15454 SDH Specifications Page 106

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Cisco ONS 15454 SDH Troubleshooting and Maintenance Guide, R3.3
May 2002
Chapter 2 General Troubleshooting
CTC Operation and Connectivity
2.3.15 VLAN Cannot Connect to Network Device from Untag Port
Symptom Networks that have a VLAN with one ONS 15454 SDH Ethernet card port set to Tagged and
one ONS 15454 SDH Ethernet card set to Untag may have difficulty implementing Address Resolution
Protocol (ARP) for a network device attached to the Untag port (Figure 2-12). They may also see a
higher than normal runt packets count at the network device attached to the Untag port.
Figure 2-12 A VLAN with Ethernet ports at Tagged and Untag
Table 2-15 describes the potential cause(s) of the symptom and the solution(s).
Workstation #1 ONS 15454
with Ethernet card
VLAN port set to Tagged
ONS 15454
with Ethernet card
VLAN port set to Untag
SDH
Ethernet
Workstation #2
76179
Table 2-15 Verify PC connection to ONS 15454 SDH (ping)
Possible Problem Solution
The Tagged ONS 15454
SDH adds the 802.1Q
tag and the Untag
ONS 15454 SDH
removes the Q-tag
without replacing the
bytes. The NIC of the
network device
categorizes the packet
as a runt and drops the
packet.
The solution is to set both ports in the VLAN to Tagged to stop the stripping
of the 4 bytes from the data packet and prevent the NIC in the network access
device from recognizing the packet as a runt and dropping it. Network
devices with 802.1Q-compliant NIC cards will accept the tagged packets.
Network devices with non-802.1Q compliant NIC cards will still drop these
tagged packets. The solution may require upgrading network devices with
non-802.1Q compliant NIC cards to 802.1Q-compliant NIC cards. You can
also set both ports in the VLAN to Untag, but you will lose 802.1Q
compliance.
Dropped packets can
occur when ARP
attempts to match the IP
address of the network
device attached to the
Untag port with the
physical MAC address
required by the network
access layer.
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