IronPort Systems 4108GL - Manual (Page 419)

18-7
Troubleshooting
Unusual Network Activity
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This can also happen, for example, if the server is first configured to issue IP
addresses with an unlimited duration, then is subsequently configured to issue
IP addresses that will expire after a limited duration. One solution is to
configure “reservations” in the DHCP server for specific IP addresses to be
assigned to devices having specific MAC addresses. For more information,
refer to the documentation for the DHCP server.
One indication of a duplicate IP address in a DHCP network is this Event Log
message:
ip: Invalid ARP source: IP address on IP address
where: both instances of IP address are the same address, indicating the
IP address that has been duplicated somewhere on the network.
The Switch Has Been Configured for DHCP/Bootp Operation, But Has
Not Received a DHCP or Bootp Reply.
When the switch is first config-
ured for DHCP/Bootp operation, or if it is rebooted with this configuration, it
immediately begins sending request packets on the network. If the switch does
not receive a reply to its DHCP/Bootp requests, it continues to periodically
send request packets, but with decreasing frequency. Thus, if a DHCP or Bootp
server is not available or accessible to the switch when DHCP/Bootp is first
configured, the switch may not immediately receive the desired configuration.
After verifying that the server has become accessible to the switch, reboot the
switch to re-start the process.
Troubleshooting CDP Operation
The switch does not appear in the CDP Neighbors table of an adjacent
CDP Device.
This may be due to any of the following:
■ Either the port connecting the switch to the adjacent device is not a
member of an untagged VLAN or any Untagged VLAN to which the
port belongs does not have an IP address.
■ If there is more than one physical path between the switch and the
other CDP device and STP is running on the switch, then STP will
block the redundant link(s). In this case, the switch port on the
remaining open link may not be a member of an untagged VLAN, or
any untagged VLANs to which the port belongs may not have an IP
address.
■ The adjacent device’s CDP Neighbors table may be full. Refer to the
documentation provided for the adjacent CDP device to determine
the table’s capacity, and then view the device’s Neighbors table to
determine whether it is full.