3troubleshootingjunos

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Troubleshooting JUNOS Platforms

Media Typ s and Int rface Naming

JUNOS platforms support s veral flavors of Ethernet. The following are the relevant media types:

Link Mode

When troubleshooting LAN topologies, consider the link mode:

•Full duplex;

•Half duplex; or

•Link bonding (802.3ad)

Fast Ethernet interfaces can support half duplex or full duplex, but Gigabit Ethernet interfaces only function in full-duplex mode.

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forDisplaying A P Table

The sh w a p no-resolve command displays the entries in the ARP table. Using the noes lve option prevents the device from attempting to determine the host name that c rresponds to the IP address.

Veri ying Cable Length

Ensure the cables used on the network do not exceed recommended lengths and meet all relevant specifications. If the cabling specifications are not met, the input errors on the interface will increase.

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•Use the show interfaces extensive command to check the status the of interface.

and displays common interface failures, su h as SONET/SDH and T3 alarms, loopbacks detected, and in reases in framing errors. If the framing errors are increasing, this in rease indi ates that frames are being corrupted. If the input errors are increasing, check the cabling to the device and have the carrier verify the integrity of the line.

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Troubleshooting JUNOS Platforms

Checking the Compatibility Mode

The subrate of an E3 or T3 interface must match that of the remote CSU exactly. The purpose of a subrate is to fit more bandwidth into an E3 or T3 circuit. To specify the subrate, include the subrate option in the compatibility-mode statement. Follow these instructions for different types of CSUs:

Ensuring Compatible Settings

The f llowing settings ensure compatibility:

•E3 and T3 frame checksums: By default, E3 and T3 interfaces use a 16-bit frame checksum. You can configure a 32-bit checksum that provides more reliable packet verification. However, some older equipment might not support 32-bit checksums.

•HDLC payload scrambling: E3 or T3 HDLC payload scrambling, which is disabled by default, provides better link stability. Both sides of a connection must either use or not use scrambling.

•Line buildout: To have the interface drive a line that is longer than 255 feet, include the long-buildout statement at the [edit interfaces interface-name t3-options] hierarchy level.

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T3 C-bit parity mode: For T3 interfaces, the C-bit parity mode controls the type of framing present on the transmitted T3 signal. When C-bit parity mode is enabled, the C-bit positions are used for the far-end block error (FEBE), FEAC, the terminal data link, path parity, and mode indicator bits, as defined in American National Standards Institute (ANSI)

T1.107a-1989. When you disable C-bit parity mode, the basic T3 framing modeReproductionis used. By default, C-bit parity mode is enabled. To disable it, include the no-cbit-parity statement at the [edit interfaces

interface-name t3-options] hierarchy level.

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Troubleshooting JUNOS Platforms

DisplayingReproductionActive Alarms

If the first line shows Physical link is Up, it means that the physical link is healthy and can pass pack ts. If the first line shows Physical link is Down, it means that the physical link is unhealthy and cannot pass packets. To display more

forextensive information about the T3 interfac if the physical link is down, use the show inte face t3-x/y/z extensive command. Look at the active alarms and active defects for the T3 interface, and troubleshoot the T3 media accordingly.