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AR Router Troubleshooting Guide

This Product Documentation provides guidance for maintaining AR Enterprise Router, covering common information collection and fault diagnostic commands, typical fault troubleshooting guide, and troubleshooting.
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When an AR Router Connects to the Internet Through Two Uplinks for Load Balancing, Some Users Cannot Open Web Pages After One Uplink Is Interrupted

When an AR Router Connects to the Internet Through Two Uplinks for Load Balancing, Some Users Cannot Open Web Pages After One Uplink Is Interrupted

This section provides a case that when an AR router connects to the Internet through two uplinks for load balancing, some users cannot open web pages after one uplink is interrupted.

Networking

Figure 28-6  Networking diagram

Fault Symptom

In Figure1, the AR functions as an enterprise's egress gateway and connects to the Internet through two uplinks (links 1 and 2) using PPPoE dial-up. The device uses equal-cost egress routes for load balancing on link 1 and link 2. Link 1 provides a bandwidth of 6 Mbit/s, and link 2 provides a bandwidth of 4 Mbit/s. NAT is configured on the device to ensure that users on the enterprise's private network can access the Internet. After link 1 is interrupted, some intranet users cannot open web pages during Internet access. In addition, the software that tests the Internet access speed shows that the Internet access speed is normal.

The AR configuration is as follows:

# 
acl number 2000 
 rule 5 permit source 192.168.0.0 0.0.255.255 
# 
interface Dialer0 
 link-protocol ppp 
 ppp chap user 123 
 ppp chap password simple 123 
 ppp pap local-user 123456 password simple 123 
 tcp adjust-mss 1200 
 ip address ppp-negotiate 
 dialer user server          
 dialer bundle 1     
 dialer timer idle 3600 
 dialer-group 1          
 nat outbound 2000     
# 
interface Dialer1 
 link-protocol ppp 
 ppp chap user 456 
 ppp chap password simple 456 
 ppp pap local-user 123456 password simple 456 
 tcp adjust-mss 1200 
 ip address ppp-negotiate 
 dialer user server 
 dialer bundle 2 
 dialer timer idle 3600 
 dialer-group 2 
 nat outbound 2000 
# 
interface GigabitEthernet1/0/0 
 pppoe-client dial-bundle-number 1 on-demand 
# 
interface GigabitEthernet2/0/0 
 pppoe-client dial-bundle-number 2 on-demand 
# 
dialer-rule 
dialer-rule 1 ip permit 
dialer-rule 2 ip permit 
# 
ip route-static 0.0.0.0 0.0.0.0 Dialer0 
ip route-static 0.0.0.0 0.0.0.0 Dialer1 
#

Fault Analysis

  1. If NAT is configured to allow intranet users to access the Internet, NAT entries are generated when users access the Internet. Run the display nat session all command, finding that the NAT entry corresponding to the outbound interface of the interrupted link has not been aged out. This fault persists after NAT entries have been deleted using the reset nat session all command in the system view.
  2. Users access the Internet using PPPoE dial-up. The protocol status of the virtual interface Dialer0 is always Up, so the route for this interface still exists in the routing table of the device though link 1 is interrupted. As a result, route selection fails and the route becomes unreachable. Run the dialer number 0 autodial command to configure automatic dial-up on the interface so that the protocol status of this interface goes Up only after the dial-up is successful. Subsequently, all users can open web pages normally, and the fault has been rectified.

Procedure

  1. Run the system-view command to enter the system view.
  2. Run the reset nat session all command to delete NAT entries.
  3. Run the interface dialer0 command to enter the Dialer0 interface view.
  4. Run the dialer number 0 autodial command to configure automatic dial-up on the interface so that the protocol status of this interface goes Up only after the dial-up is successful.
  5. Perform steps 3 and 4 in the Dialer1 interface view.

Suggestion

  1. If you configure NAT for Internet access and need to change the outbound interface of the network, you are advised to delete NAT entries after the change. This operation prevents the problem that users cannot access the Internet because the NAT entry corresponding to the outbound interface is not aged out.
  2. The protocol status of a virtual interface is always Up. If a virtual interface has been configured and a route forwarding failure occurs, you are advised to check whether the routing entry corresponding to the virtual interface exists.
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Updated: 2019-05-10

Document ID: EDOC1000079719

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