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An offline AP is still displayed as "Online" on the AC

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Post time 2018-4-9 11:24:02 | Show all posts |Read mode
An offline AP is still displayed as"Online" on the AC.

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 Author| Post time 2018-4-9 11:25:33 | Show all posts
[Analysis]

1. Run the show run and showap-configrun commands to display the configuration and check whetherecho-interval is changed. (The default value is 30s.)

2. The result shows that the parameter valueis still the default value. On the AC, run the show capwap index detail command several times. The keepalive valueremains unchanged. It is suspected that the AP status is not updated on the ACbecause the keepalive function is disabled. Run the show capwap [ip addr] detail | inc Echo command. The result shows thatthe echo-interval is 0s.
AC-branch(config-ap)#show capwap10.121.121.129 detail | in Echo
Echointerval is 0 secs, Dead interval is 0 secs Expire 4294967237 secs

3. Run the show cli record command to display the AC historical commandrecords. The result shows that echo-interval disable is set for the AP-Group ofthe AP. Delete the configuration, the problem is solved.

[Summary]
This fault is caused by incorrectconfiguration of the hidden command. echo-interval disable is used to disablethe echo function of the CAPWAP tunnel. After configuration, the AP echofunction is disabled and the status of the AP is still displayed as"Run" after the AP goes offline. Besides, echo-interval disable isnot displayed in the show runcommand.

The default echo interval between an AP andan AC is 30s. If the AC does not receive any echo packet from the AP within30s, the AP goes offline.
The AP keeps alive the tunnel by sending anecho request every 30s. After receiving the echo request, the AC sends an echoresponse. If receiving no echo response within a certain period of time, the APresends the echo request. The first retransmit starts at the 3rd second. Whenthe time reaches the half of the echo interval, the AP deems that the tunnel isdisconnected. The AP performs five retransmits within the 30s echo interval,that is, the 3rd second, 6th second, 12th second, 15th second, and 15th second.

Even if the echo interval is changed to another value, thecalculation method for the retransmit time and count is still the same. Theecho interval range is 5-255s, which is configured by the echo-interval *command in AP orAP group configuration mode.

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