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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 10 Configuring LRE
Configuring LRE Ports
Note Th e margin co mm an d is effective with any profile, but only in conj unct ion w ith rate select ion an d only
when a link is being activated.

LRE Link Persistence

A brief LRE link do wn and up transitio n can cause the rest of the IOS module s to react immediately, for
example, th e Dyna mic MAC addresse s ar e re moved from tha t po rt s table . You ca n use t he l ink
persiste nc e fe atur e to co nfigure a del ay du ra tio n o n the Cata lyst 295 0 L RE o f up to 20 sec ond s befo re
link failure is reported.
Refer to the lre persistence reference pages in the Catal yst 2950 Desktop Switch C om mand R eference
for further details.

LRE Li nk Monito r

You can use the li nk moni tor feat ure t o trac k unde sira ble or inte rest ing c ond ition s on a l ink a nd to take
system-defined actions after certain thresholds are reached. The link monitor can track these conditions:
•SNR, in decibels (db): The link must have a minim um SNR to functio n; a higher SNR value means
a better noise margin on the link. Links are not establish if the SNR is insufficient. (See the “Link
Qualification and SNR Margins” se ctio n on pa ge 10-12 for more information.)
•Reed- Solomon (RS) errors: The RS For ward Error Correction circ uit corrects small b ursts of errors
so that noise events do not cause Ethernet FCS errors. This is implemented in the octal chip as a
32-bit counter. The count resets on read.
•Transmit (TX) Power, in dBm/Hz: This is fixed for the switch and adjusts automatically for the
CPE device. T he l oca l t ransm i t power i s a lways con sta nt an d th e sam e fo r a given profile. The
remote transmit power varies according to distance from the switch to the CPE device, with a
minimum t ransmit power of 91.9 dBm /Hz (c orrespond ing to short di stance s) and a maxi mum
transmit power of -55 dBm/Hz (corresponding to longer cable lengths or greater cable attenuation).
The CPE device’s power can reac h its maxim um at dista nces betwee n 1500ft/ 450m an d
3000ft/900m.
•Software controlled Automatic Gain Control (SW AGC Gain), in dBm: This gives an indirect
meas ure of th e received power level. Higher valu es mea n that the rece ive pow er is l ower (and thu s
in nee d of mo re boost ) .
Command Purpose
Step 1 configure terminal Enter globa l configurati on mode.
Step 2 interface LRE-interface Enter int erface co nfiguration mo de, an d enter the number of the
LRE po rt to b e co nfigured .
Step 3 persistence time Enter the length of ti me (in seconds ) you wis h to set for the
persistence. (The default is 3 seconds)
Step 4 end Return to privileged EXEC mode.
Step 5 show controllers lre status persistence Verify the change.