3troubleshootingjunos

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Standard Interface Status

Use the show int rfac s command without the terse or detailed switches to

display standard information about the named interface (or all interfaces when you do

not identify a specific interface). The slide provides sample output for an OC-3C

SONET inte face. The callouts the slide help illustrate how interfaces partition into

physical devices and logical units in JUNOS Software.

Each physical and logical interface is referenced by two index numbers within JUNOS

S twa e. An inte face index is assigned to each interface at boot time depending

up n the rder in which that interface activates. The SNMP ifIndex is used to

identi y and reference that interface when performing SNMP MIB walks. Note that the

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indexes assigned to the physical interface device (ifd) differ from the index used to

foridentify the logical device (ifl). Wherever possible, the SNMP ifIndex values are

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Give-Up: Link protocol does not continue to attempt to connect after

repeated failures;

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Keepalives: Link protocol keepalives are enabled;

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Loose-LCP: PPP does not use Link Control Protocol (LCP) to i dicate

whether the link protocol is up;

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Loose-LMI: Frame Relay will not use Local Management Interface (LMI)

to indicate whether the link protocol is up;

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Loose-NCP: PPP does not use Network Control Pro ocol (NCP)

indicate whether the device is up; and

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No-Keepalives: Link protocol keepalives are disabled.

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Displaying Input and Out ut Errors for the Interface

Use the show int rfac s extensive command to display input errors

(extensive output only) the interface. Use the clear interfaces

statistics interface-name command to reset the counters for the specified

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inte face; omit an interface name to clear all interface statistics. The following list

explains some of the less obvious counters:

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Errors: Displays the sum of the incoming frame aborts and FCS errors.

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Policed discards: Displays the frames that the incoming packet

match code discarded because they were not recognized or were not of

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interest. Usually, this field reports protocols that JUNOS Software does

frame.

not handle, such as Cisco Discovery Protocol (CDP), Spanning Tree

Protocol (STP), or any protocol type that JUNOS Software does not

understand. (On an Ethernet network, numerous possibilities exist.)

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L3 incompletes: This counter increments when the incoming packet

fails Layer 3 (usually IPv4) checks of the header. For example, a frame

with less than 20 bytes of available IP header would be discarded, and

this counter would increment.

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L2 channel errors: This counter increments when the software

cannot find a valid logical interface (such as e3-1/2/3.0) for an incoming

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L2 mismatch timeouts: Displays the count of malformed or short

packets that cause the incoming packet handler to discard the frame as

unreadable.

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SRAM errors: This counter increments when a hardware error occurs

in the static RAM on the PIC. The value in this field should always be 0. If

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it increments, the PIC is malfunctioning.

The show interface extensive command also displays the output errors on

the interface. The following list explains the less obvious counters:

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HS link CRC errors: Displays the count of errors on the h gh-speed

links between the application-specific integration circu s (ASICs)

responsible for handling the router interfaces.

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Carrier transitions: Displays the number of imes he in erface

has gone from down to up. This number should not in rement quickly,

increasing only when the cable is unpl gged, the far-end system powers

on and off, or a similar problem occurs. If it does increment quickly

(perhaps every 10 seconds), then either the transmission line, the

far-end system, or the PIC is broken.

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Errors: Displays the sum f the utg ing frame aborts and FCS errors.

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Drops: Displays the number f packets dropped by the output queue of

the I/O Manager ASIC. If the inte face is saturated, this number

increments once for eve y acket that the ASIC’s random early detection

(RED) mechanism d o s.

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Aged pack ts: Dis lays the number of packets that remained in

shared pack SDRAM for so long that the system automatically purged

them. The value in this field should never increment. If it does, it is most

likely a software bug or possibly due to malfunctioning hardware.

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You can use a similar approach to track down noise on a line by combining the looping

process with a test that checks for bit rate errors, commonly known as BERT testing.

Many of the interfaces JUNOS platforms support BERT testing.

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rem te l pbackReproductionequest to the remote device. Line loops can be remotely

signalled

Supported Loopback Ty

s

Most PICs supported

JUNOS platforms support local (internal) loopback tests.

Where possible, it is b

st to p

rform local loopbacks using an external loopback plug