Networking Knowledge Base

Core IssueThe Cisco IOS  Software image is not appropriate for the router, or it is corrupted.ResolutionErase the Flash, and download a new valid Cisco IOS Software image.  For information on how to erase the Flash, refer to PCMCIA Filesystem Compati...

Core IssueWhen a router forwards a multicast packet from one interface to another, it decrements the Time To Live (TTL) value in the IP header by one. It sends the packet only if the resulting TTL value is not zero and is greater than the multicast T...

Core IssueIf a Cisco IOS  Software upgrade is performed by issuing the xmodem command from ROM Monitor (ROMmon) mode, and the router boots successfully but no image is in the Flash, then the [-r] option was used when the xmodem command was issued.The...

Core IssueThe issue occurs when an Asynchronous Transfer Mode (ATM) exists in the 7200VXR and attempts are made to set an external clock or clock from the line, but the clock status appears to still be internally clocked.In order to confirm the Cisco...

ResolutionThis example shows how to configure the FastEthernet port on an 1841 router as a trunking interface. The Cisco 1841 router has two onboard FastEthernet autosensing interfaces that support 10- or 100-Mbps connections.The sub interface become...

Core issueThe crash occurs when a vlan.dat NVRAM file is corrupt. One important step is missing in the Step-by-Step Procedure to Convert from CatOS to Cisco IOS System Software in System Software Conversion from CatOS to Cisco IOS for Catalyst 6500/6...

Core issueThe default form of error message is:%C4K_L2MAN-6-INVALIDSOURCEADDRESSPACKET: Packet received with invalid source MAC address ([mac-addr] ) on port [char] in vlan [dec] This means a packet was received with an all zero (00:00:00:00:00:00) o...

Core IssueOn most class B Flash file systems, you can partition banks of Flash memory into separate, logical devices so that the router can hold and maintain two or more different software images. This partitioning allows you to write software into F...

Core IssueWhen troubleshooting Ethernet media, the show interfaces ethernet and show interfaces fastethernet privileged EXEC commands provide several key fields of information that can help you isolate problems related to Ethernet interfaces. These a...

SolutionIf an XOR mathematical operation is performed on the last two bits of the source MAC address and the destination MAC address, the operation yields one of four results:(0 0)(0 1)(1 0)(1 1) Each of these values points to a link in the Fast Ethe...

Core IssueCisco processors have timers that guard against certain types of system hangs. The CPU periodically resets a watchdog timer. The watchdog timer basically controls the time of each process. If the timer is not reset, a trap occurs. If a proc...

ResolutionWhen two line cards of different revision numbers are used, there is no adverse effect on the performance of the line cards (even when installed in one chassis).For example, this scenario presents no issue:Two similar types of line cards ar...

Core IssueAn Intermediate System-to-Intermediate System (IS-IS) level router is aware only of the topology of its own area. To route packets destined for networks outside its own area, the Level 1 (L1) router relies on the default route injected by a...

Core IssueThese error messages do not necessarily indicate a Hot Standby Router Protocol (HSRP) problem. Rather, the error messages usually indicate a possible Spanning Tree Protocol (STP) loop or router-switch configuration issue.The IP address in a...

Core IssueThese are Versatile Interface Processor (VIP) 2 parity errors:processor memory parity error exceptionreno read parity errorI/O controller parity errorpacket memory read parity errorProtocol Control Information (PCI) bus parity errorCyASIC p...