Cisco 2600XM Series Installation Guide download pdf (Page 14)

Router Is Dropping Packets

Packet loss caused by hardware problems is fairly easy to identify. The following section uses the output of

the show interfaces command to identify packet loss.

Cyclic Redundancy Check (CRC) and Frame Errors

If CRC errors or frame errors are constantly increasing on the interface, this usually indicates a hardware

problem.

router#show interface ethernet 0/0

Ethernet0/0 is up, line protocol is up

...

121 input errors, 102 CRC, 19 frame, 0 overrun, 0 ignored

An exception to this is when CRC and frame errors are found on channelized interfaces; these can also

indicate clocking problems. The fault that is causing the errors can be anywhere between two connected

interfaces − on cables, intermediate devices, or on interfaces themselves. Troubleshooting techniques differ

slightly for different interface types.

Ethernet Interfaces

For Ethernet interfaces, troubleshooting differs between a shared environment (devices connected through a

hub or with a coaxial cable) and a switched environment (devices connected to a switch).

In a switched environment, there are only five components that could cause the error:

cable•

local interface (port)•

remote interface (port)•

speed•

duplex mismatch•

Consequently, the troubleshooting steps are simple. For example, if a router is connected to a switch, the

troubleshooting steps would be:

Replace the cable.1.

If this does not solve the problem, try another port on the switch.2.

If the problem persists, replace the Ethernet interface.3.

In a shared environment, the source of the problem is a lot harder to find. Every piece of hardware that makes

up the shared segment can be the cause. All components (cables, connectors, and so on) have to be tested one

by one.

Ignored Packets

Packets are ignored if there are no free buffers to accept the new packet. This can happen if the router is

overloaded with traffic, but can also happen if the interface is faulty.

router#show interfaces ethernet 0/0

Ethernet0/0 is up, line protocol is up

...

21 input errors, 0 CRC, 0 frame, 0 overrun, 21 ignored

Cisco − Hardware Troubleshooting for the Cisco 2600 Series Router

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Cisco 2600XM Series Installation Guide Page 14