Why is the dialer interface still Up when the physical status of the dialer interface is Down

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When the physical interface that is not connected to a cable is Down, the dialer interface displays Snoofing Up. This situation is normal. You can run the dialer number 1 autodial command so that the dialer interface changes as the physical interface.

Other related questions:
What are the differences between a dialer interface and a physical interface
For C-DCC, a dialer interface may contain multiple physical interfaces, but a physical interface belongs to only one dialer interface and uses one set of dialer parameters. For RS-DCC, a dialer interface may contain multiple physical interfaces, and a physical interface can belong to multiple dialer interfaces.

Why the physical interface status of a 3G cellular interface is Down

If the physical status of a 3G cellular interface (cellular interface) is Down, no 3G link is established and data service has not been transmitted yet. That is, no dialup is triggered or dialup fails on the 3G link.

NOTE:

If no dialup is triggered or dialup fails on a 3G link, the physical interface status is still Down even if a 3G data card (3G modem) is installed.


Internet access is slow after a PPPoE dialup link on an AR router is switched over
Modify the TCP MSS value of the device, and set the state of the Dialer interface protocol after PPPoE dialup fails to Down for link switchover. Example: Modify the TCP MSS value. system-view [Huawei]interface Dialer 1 [Huawei-Dialer1]tcp adjust-mss 1200 Example: Set the state of the Dialer interface protocol after PPPoE dialup fails to Down. system-view [Huawei]interface Dialer 1 [Huawei-Dialer1]dialer number 1 autodial The causes are as follows: The TCP MSS value is used to control the maximum transmission load of TCP packets, and it is determined according to the negotiation between the client and server. Generally, it is set to 1460. Plus 20-byte IP header, 20-byte TCP header, and 8-byte PPPoE header, the MTU of TCP packets is 1508 bytes. However, the MTU of network device interfaces is 1500 bytes generally. Since TCP packets cannot be fragmented (according to DF flag in the IP header of the packets defined in the protocol), they will be discarded. As a result, Internet access slows down. Modify the TCP MSS value to enable the router to join in the MSS value negotiation process, and therefore avoid packet discarding during TCP transmission. The Dialer interface is a virtual service bearing interface of devices, and it is invisible on the device panel. This interface is snooping up, which causes switchover failures if the router attempts to switch over to a normal physical interface after dialup fails. Run the dialer number 1 autodial command to ensure that the state of the interface is Down after dialup fails and the route to the Dialer interface is canceled. Then, link switchover can be implemented.

How do I configure a 3G interface on an AR router
When WCDMA is used, the procedure for configuring a 3G interface is as follows: [Huawei] apn profile 3gprofile //Create an APN profile. [Huawei-apn-profile-3gprofile] apn 3GNET [Huawei-apn-profile-3gprofile] user name 3guser password cipher Password@123 authentication-mode auto [Huawei-apn-profile-3gprofile] quit [Huawei] dialer-rule //Configure a dialer ACL. [Huawei-dialer-rule] dialer-rule 1 ip permit [Huawei-dialer-rule] quit [Huawei] interface cellular 0/0/0 [Huawei-Cellular0/0/0] link-protocol ppp [Huawei-Cellular0/0/0] ip address ppp-negotiate //Configure an IP address through PPP negotiation. [Huawei-Cellular0/0/0] ppp ipcp dns request //Configure a DNS server address through PPP negotiation. [Huawei-Cellular0/0/0] dialer enable-circular //Enable C-DCC. [Huawei-Cellular0/0/0] dialer-group 1 //Associate Cellular0/0/0 to the dialer access group. [Huawei-Cellular0/0/0] dialer number *99# //Configure a dialer number for calling the remote end. [Huawei-Cellular0/0/0] mode wcdma wcdma-precedence //Configure a network connection mode. [Huawei-Cellular0/0/0] apn-profile 3gprofile //Bind the APN profile to the 3G cellular interface. [Huawei-Cellular0/0/0] shutdown [Huawei-Cellular0/0/0] undo shutdown [Huawei-Cellular0/0/0] quit When CDMA2000 is used, the procedure for configuring a 3G interface is as follows: [Huawei] dialer-rule //Configure a dialer ACL. [Huawei-dialer-rule] dialer-rule 1 ip permit [Huawei-dialer-rule] quit [Huawei] interface cellular 0/0/0 [Huawei-Cellular0/0/0] link-protocol ppp [Huawei-Cellular0/0/0] ip address ppp-negotiate //Configure an IP address through PPP negotiation. [Huawei-Cellular0/0/0] ppp ipcp dns request //Configure a DNS server address through PPP negotiation. [Huawei-Cellular0/0/0] dialer enable-circular //Enable C-DCC. [Huawei-Cellular0/0/0] dialer-group 1 //Associate Cellular0/0/0 to the dialer access group. [Huawei-Cellular0/0/0] dialer number #777 //Configure a dialer number for calling the remote end. [Huawei-Cellular0/0/0] mode cdma hybrid //Configure a network reconnection mode. [Huawei-Cellular0/0/0] quit

The PPPoE physical interface is Up but the state of the protocol is Down
After a PPPoE dialup, all services are born on the Dialer interface, with corresponding physical interface being Up and protocol being Down, which is normal and does not affect the services and use. Ignore it. A virtual interface is needed for PPPoE dialup to bear all services. Pay attention to the Dialer interface, and the protocol status does not need to be concerned with.

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