One core node of bearer network NE80 connects NE40 through E1 bundling. The version is Version 3.10, RELEASE 2222. One day the link between NE40 and NE80 is interrupted. NE40 attaches softswitch service and switches over old network. NE80 and NE40 display bundled serial link of MPgroup is invalid. For serial link the physical state is up and the protocol state is down. Check the log and on one operates.
Network managment center has alarm and it displays NE40 is out of control. Softswitch service switches over old network.
1. Check transmission link. There is problem during interruption, but it recovers after a while.
2. Serial link under MPgroup is invalid. The physical state is up and the protocol state is down.
3. Check logbuffer and no one changes the command.
4. Check configuration and IP address under NE40 and NE80. It is normal.
5. Check username and password of AAA view under NE80 and NE40. It is found that NE80 does not add username and password of NE40.
6. Add username and password of NE40 under NE80 and the link recovers.
It is doubted that encapsulation protocol of Serial link is problematic. Login on NE80 and NE40 and check configuration of interrupted serial port:
NE80: interface Serial2/0/0/1:0
ppp authentication-mode pap
ppp pap local-user CR1-1 password simple CR1-1
NE40: interface Serial1/0/0/1:0
ppp authentication-mode pap
ppp pap local-user XZLS-CR1-1 password simple XZLS-CR1-1
Clock configuration is not problematic and the encapsulation is PPP-PAP protocol. PAP (Password Authentication Protocol) authentication is twice handshake authentication and the password is clear text. For PAP authentication, the authenticated part need send username and password to the authenticating part. The authenticating part checks whether there are username and password of the authenticated part according to local users table. And then it returns different response (receive or refuse).
The interface of both sides of transmission device configures username and password of PAP and it is not problematic. The authentication of username and password is problematic. Check AAA configuration under NE80 and it is found that it does not add username and password of NE40. There is username and password of NE80 on AAA configuration of NE40. Add username and password of NE40 in AAA view on NE80 to local users list. The link recovers.
Check the log and local-user XZLS-CR1-1 password simple XZLS-CR1-1 under AAA authentication of NE80 device is wrongly deleted by the engineer. It has been done several days ago. It does not cause link interruption. PPP-PAP authentication does not send authentication username and password when the authentication passes. Before the interruption the transmission link is problematic. The physical state of the link is down. After the transmission recovers, LCP sets up connection. Username and password do not pass. NCP connection fails and PPP connection cannot be established.
For the change of users under AAA view, notice whether the service type is PPP.