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Cisco ONS 15454 SDH Troubleshooting Guide, R5.0
July 2005
Chapter 1 General Troubleshooting
1.10.16 VLAN Cannot Connect to Network Device from Untag Port
c. If a port is not assigned to the correct VLAN, click that port column in the VLAN row and set the
port to Tagged or Untag.
d. Click Apply.
Step 8 Repeat Step 7 for devices B and D.
Step 9 Verify that the Ethernet circuit that carries VLAN No. 1 is provisioned and that ONS 15454 SDH No. 1
and ONS 15454 SDH No. 2 ports also use VLAN No. 1.
1.10.16 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 might have difficulty implementing Address Resolution
Protocol (ARP) for a network device attached to the Untag port (Figure 1-50). They might also see a
higher than normal runt packets count at the network device attached to the Untag port. This
symptom/limitation also exists when ports within the same card or ports within the same chassis are put
on the same VLAN, with a mix of tagged and untagged.
Possible Cause The Tagged ONS 15454 SDH adds the IEEE 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.
Possible Cause Dropped packets can also 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.
Recommended Action 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 card in the network access device from
recognizing the packet as a runt and dropping it. Network devices with NIC cards that are not
IEEE 802.1Q-compliant accept the tagged packets. Network devices with NIC cards that are not
IEEE 802.1Q compliant still drop these tagged packets. The solution might require upgrading
network devices with NIC cards that are not IEEE 802.1Q compliant to IEEE 802.1Q-compliant NIC
cards. You can also set both ports in the VLAN to Untag, but you lose IEEE 802.1Q compliance.
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