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How NetFlow works when only one of the two supervisors has a NetFlow Services Card (WS-F4531) in Cisco Catalyst 4500/4000 running Cisco IOS

Core issueThe Cisco Catalyst 4000 NetFlow Services Card (WS-F4531) is an optional daughter card for the Catalyst 4000/4500 Supervisor Engine IV or Supervisor Engine V. In Supervisor Engine V-10GE, the NetFlow functionality is embedded in the supervis...

Configuring EtherChannel results in ports being errdisabled, and fails to form channels due to spanning tree loops caused by VLAN misconfiguration

Core issueIf ports (2/1-4) forming an EtherChannel have inconsistent VLAN configuration, on the one side (A) set to AUTO mode, and the other side (B) is correctly configured but set to ON, Spanning-Tree Protocol (STP) errors can be generated during E...

After increasing the console port's speed to perform an xmodem transfer and then changing the configuration register back to the default, the new configuration register value does not change after reloading the router due to the speed command not being is

Core IssueThis issue may result in the new value not holding after the reload.ResolutionTo ensure that the configuration register value is set back to the default (after changing the console speed for an xmodem transfer), perform these steps:After th...

Frequently asked questions about NAT

Core IssueNetwork Address Translation (NAT) replaces IP addresses within a packet with different IP addresses. It is useful in the following instances:To conserve IP addressesTo connect a private network with an unregistered address to a public netwo...

Classful networks generated with the network BGP configuration command are not advertised by BGP

Core IssueA valid route must exist in the routing table for Border Gateway Protocol (BGP) to advertise a classful network by issuing the network configuration command (under router BGP).ResolutionTo resolve this issue, ensure that a valid route exist...

The Cisco Catalyst 6500 "show module" command output shows a module diagnostic status of "bypass" for all of the line cards

Core issueThe show module command output shows the status as bypass because the diagnostic level is configured as bypass for some reason. ResolutionThe default diagnostic mode is minimal, whether the software is Catalyst OS (CatOS) or Cisco IOS . The...

The "%UDLD-3-AGGRDISABLE" error message is displayed in the logs of a Catalyst 6500 series switch

Core issueThis message indicates that a fault has been detected in an Ethernet port connection, and that the port has been disabled in order to prevent other protocols from malfunctioning:%UDLD-3-AGGRDISABLE: Neighbor(s) of port [dec]/[dec] disappear...

The OSPF demand circuit is going up and down

Introduction:As per RFC 1793,extending OSPF to support demand cicuits,"OSPF hellos and the refresh of OSPF routing information are suppressed on demand circuits,allowing the underlying data-link connection to be closed when not carrying application ...

Multi-VLAN configuration does not work due to TRUNKING enabled on port

Core issueThe multi-VLAN port feature on the Catalyst 2900 XL/3500 XL switches allows for configuring a single port into two or more VLANs. This feature allows users from different VLANs to access a server or router without implementing inter-VLAN ro...

EIGRP route is not installed into the routing table

Core IssueEnhanced Interior Gateway Routing Protocol (EIGRP) builds a topology table with metrics of feasible distance and reported distance for each route. To see the table, issue the ip eigrp topology command.All the routes with a feasible distance...

How does BGP determine the best path among the multiple paths in its BGP table to be installed into the IP routing table?

ResolutionBorder Gateway Protocol (BGP) routers typically receive multiple paths to the same destination. The BGP best path algorithm decides which is the best path to install in the IP routing table and to use for forwarding traffic.For a list of ru...

Loopback is advertised as a host route /32 instead of the actual subnet that is configured

ResolutionLoopbacks are considered host routes in Open Shortest Path First (OSPF). To make OSPF advertise the loopback subnet as the actual subnet with the loopback mask, instead of as host route /32, issue the ip ospf network point-to-point command...

Redundant supervisor engines do not synchronize

Core issueA hardware mismatch between redundant supervisors and daughter cards causes this synchronization problem.High availability redundancy minimizes the time taken to switch over from the active supervisor engine to the standby supervisor engine...

Catalyst 3550 switch reloads and gives the "%EXPRESS_SETUP-6-CONFIG_IS_RESET" error message when the mode button is pressed for a longer time during a password recovery

Core issueThe EXPRESS_SETUP-6-CONFIG_IS_RESET: [chars] error message means the configuration is reset. [chars] is a text message that clarifies the reset event.If you press the Mode button for a total of 10 seconds or more in a switch configured for ...

Flash memory shows as Read Only in the output of the show version or show flash commands

Core IssueRouters that run Cisco IOS Software from Flash have a feature called Flash Load Helper (FLH). When this is present in both Cisco IOS Software and ROM, the Flash is set to Read Only.ResolutionBecause this is a cosmetic issue, it does not p...