Linux PPPoE接続に時々認証失敗が表示されるのはなぜですか?

Linux PPPoE接続に時々認証失敗が表示されるのはなぜですか?

これは私のログです:

Oct 18 09:51:52 -desktop pppd[2764]: Plugin rp-pppoe.so loaded.
Oct 18 09:51:52 -desktop pppd[2766]: pppd 2.4.5 started by root, uid 0
Oct 18 09:51:52 -desktop pppd[2766]: PPP session is 15207
Oct 18 09:51:52 -desktop pppd[2766]: Connected to <eth addr> via interface eth0
Oct 18 09:51:52 -desktop pppd[2766]: Using interface ppp0
Oct 18 09:51:52 -desktop pppd[2766]: Connect: ppp0 <--> eth0
Oct 18 09:51:53 -desktop pppd[2766]: CHAP authentication failed: bad username or password
Oct 18 09:51:53 -desktop pppd[2766]: CHAP authentication failed 
Oct 18 09:51:53 -desktop pppd[2766]: Connection terminated.
Oct 18 09:52:23 -desktop pppd[2766]: PPP session is 15209
Oct 18 09:52:23 -desktop pppd[2766]: Connected to <eth addr> via interface eth0
Oct 18 09:52:23 -desktop pppd[2766]: Using interface ppp0
Oct 18 09:52:23 -desktop pppd[2766]: Connect: ppp0 <--> eth0
Oct 18 09:52:23 -desktop pppd[2766]: CHAP authentication failed: bad username or password
Oct 18 09:52:23 -desktop pppd[2766]: CHAP authentication failed 
Oct 18 09:52:23 -desktop pppd[2766]: Connection terminated.
Oct 18 09:52:53 -desktop pppd[2766]: PPP session is 13921
Oct 18 09:52:53 -desktop pppd[2766]: Connected to <eth addr> via interface eth0
Oct 18 09:52:53 -desktop pppd[2766]: Using interface ppp0
Oct 18 09:52:53 -desktop pppd[2766]: Connect: ppp0 <--> eth0
Oct 18 09:52:53 -desktop pppd[2766]: CHAP authentication succeeded: Welcome.
Oct 18 09:52:53 -desktop pppd[2766]: CHAP authentication succeeded
Oct 18 09:52:53 -desktop pppd[2766]: peer from calling number <eth addr> authorized
Oct 18 09:52:53 -desktop pppd[2766]: local  IP address 
Oct 18 09:52:53 -desktop pppd[2766]: remote IP addres
Oct 18 09:52:53 -desktop pppd[2766]: primary   DNS address 
Oct 18 09:52:53 -desktop pppd[2766]: secondary DNS address 
Oct 18 09:52:53 -desktop pppd[2766]: CCP terminated by peer (No compression negotiated^@)
Oct 18 09:52:53 -desktop pppd[2766]: Compression disabled by peer.

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