Specifications

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Cisco ONS 15454 Troubleshooting and Maintenance Guide
November 2001
Chapter 2 General Troubleshooting
e. It is possible that the Ethernet port is functioning properly but the LNK LED itself is broken. Run
the procedure in the “Lamp Test for Card LEDs” section on page 2-37.
Step 6 Verify connectivity between device A and device C by pinging between these locally-attached devices
(see the “Verify PC Connection to ONS 15454 (ping)” section on page 2-23). If the ping is unsuccessful:
a. Verify that device A and device C are on the same IP subnet.
b. At the card view in CTC, display the Ethernet card and click the Provisioning > VLAN tabs to
verify that both Port 1 and Port 3 on the card are assigned to the same VLAN.
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. Click Apply.
Step 7 Repeat Step 6 for devices B and D.
Step 8 Verify that the Ethernet circuit that carries VLAN #1 is provisioned and that ONS 15454 #1 and ONS
15454 #2 are included in circuit VLAN #1.
2.3.15 VLAN Cannot Connect to Network Device from Untag Port
Networks that have a VLAN with one ONS 15454 Ethernet card port set to Tagged and one ONS 15454
Ethernet card set to Untag may have difficulty implementing Address Resolution Protocol (ARP) for a
network device attached to the Untag port. They may also see a higher than normal runt packets count
at the network device attached to the Untag port.
This implementation problem occurs because the port of the ONS 15454 Ethernet card that is set to
Tagged adds the 802.1Q tag, which is four bytes long, to a 60-byte packet and sends the packet to the
ONS 15454 with the Ethernet card port set to Untag. The second ONS 15454 removes the 4-byte 802.1
Q-tag and does not stuff the packet with four replacement bytes. This 64-byte packet drops in size to 60
bytes, which makes it a runt or illegal Ethernet packet. The NIC of the network device categorizes the
packet as a runt and drops the packet.
Figure 2-13 A VLAN with Ethernet ports at Tagged And Untag
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. ARP uses
broadcast data packets which are often 60 bytes plus an additional 4 bytes of 802.1 Q-tag information.
This makes ARP especially vulnerable to the runt problem.
55243
Workstation #1 ONS 15454
with Ethernet card
VLAN port set to Tagged
ONS 15454
with Ethernet card
VLAN port set to Untag
SONET
Ethernet
Workstation #2