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Troubleshooting
Unusual Network Activity
■ 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.
One or more CDP neighbors appear intermittently or not at all in the
switch’s CDP Neighbors table. This may be caused by more than 60 neigh-
boring devices sending CDP packets to the switch. Exceeding the 60-neighbor
limit can occur, for example, where multiple neighbors are connected to the
switch through non-CDP devices such as many hubs.
The Same CDP Switch or Router Appears on More Than One Port in
the CDP Neighbors Table. Where CDP is running, a switch or router that is
the STP root transmits outbound CDP packets over all links, including redun-
dant links that STP may be blocking in non-root devices. In this case, the non-
root device shows an entry in its CDP Neighbors table for every port on which
it receives a CDP packet from the root device. See
“Effect of Spanning Tree
(STP) On CDP Packet Transmission” on page 13-36.
IGMP-Related Problems
IP Multicast (IGMP) Traffic That Is Directed By IGMP Does Not Reach
IGMP Hosts or a Multicast Router Connected to a Port. IGMP must
be enabled on the switch and the affected port must be configured for “Auto”
or “Forward” operation.
IP Multicast Traffic Floods Out All Ports; IGMP Does Not Appear To
Filter Traffic. The IGMP feature does not operate if the switch or VLAN does
not have an IP address configured manually or obtained through DHCP/Bootp.
To verify whether an IP address is configured for the switch or VLAN, do either
of the following:
■ Try Using the Web Browser Interface: If you can access the web
browser interface, then an IP address is configured.
■ Try To Telnet to the Switch Console: If you can Telnet to the switch,
then an IP address is configured.
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