Cisco Systems DOC-7814982 Preventing Autone gotiation Mismatc hes, Troubleshooting LRE Port Configuration

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Catalyst 2950 Desktop Switch Software Configuration Guide
78-14982-01
Chapter 28 Troubleshooting
Preventing Autonegotiation Mismatches
Preventing Autone gotiation Mismatc hes
The IEEE 802.3AB autonegotiation protocol manages the switch settings for speed (10 Mbps, 100 Mbps,
and 1000 Mbps excluding GBIC ports) and duplex (half or full). There are situations when this protocol
can inc orrect ly align t hese sett ings, re ducing pe rform ance. A mismatch occur s under these
circumstances:
•A manual ly-se t speed or duplex p aramete r is different fro m the manu ally set speed or dupl ex
parame ter o n th e co nnec ted por t.
•A port is set to autonegotiate, and the connected port is set to full duplex with no autonegotiation.
To maximize switch performance and ensure a link, follow one of these guidelines when changing the
setting s for duplex and s peed:
•Let both por ts autonegoti ate both spee d and duplex.
•Manual ly set the speed an d duplex param eters fo r the ports on both end s of the co nnectio n.
Note If a r emot e device do es n ot aut onegoti ate , con figure the dup lex setti ngs o n the two por ts t o ma tc h. The
speed parameter can adjust itself even if the connected port does not autonegotiate.
Troubleshooting LRE Port Configuration
Table 28-4 l ist s pro blem s tha t y ou migh t enc oun ter wh en con figurin g an d m oni tor ing t h e Long- Rea ch
Ethernet (LRE) ports on the Catalyst 2950 LRE switches. For additional information about what can
affect LR E conne ction s, see the “Environmenta l Consider ations fo r LRE Links ” section on pa ge 7-18.
LRE command descriptions provide additional troubleshooting information. Refer to the switch
comm an d ref e renc e.
See the Re lease Notes for the Catalyst 2950 Desktop Switch, Re lease 12.1(11) YJ for switch upgrade and
CPE device upg rade tro uble sho oting infor ma tion.
Table 28-4 LRE Port Problems
Probl e m Suspected Cause and Su ggested So l uti on
Amber LRE port LED The switch and CPE device are unable to establish an LRE link using the selected profile.
•Change to a profile with a lower data rate (for example, use LRE-5 instead of LRE-15).
•Reduce the effect of stubs or bridge taps by terminating them with 300-ohm microfilters.
Excessive CRC errors
on an LRE link •A noisy environment (such as mot ors and power surges) is causing inter ferenc e with the LRE
link.
– Cha nge to a profile that ha s the interle aver fe ature e nabled , such as the L RE-5, L RE-10,
LRE-1 5, LR E-10-1, LR E-10- 3, or LRE-10- 5 profile.
– Change to a profile with a lower data rate (for example, use LRE-5 instead of LRE-15) to
increase the noise margin.
•The LRE link length and quality are close to the limit of operation.
– Change t o a lower pro file (for exam ple , LRE -5 inst ea d o f LRE-1 5).
– Reduce the effect of stubs or bridge taps by terminating them with 300-ohm microfilters.