AC6605 Access Controller
Dual-Link Backup White Paper
1
Dual-Link Backup
Issue 01 (2012-05-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
7
Revertive Switchover
After the original active AC recovers and the AP sets up a CAPWAP tunnel with this AC, the
AP triggers a revertive switchover after a delay time to avoid frequent switchovers caused by
network flapping. The delay time is fixed at 500 seconds, which is 20 times the Echo interval.
When the delay expires, the AP sends an Echo packet to request the ACs to carry out a
revertive switchover. Additionally, the AP transfers STA data to the new active AC.
1.3.5 Loop Prevention in VLANs
As shown in Figure 1-2, AC1 and AC2 work in dual-link backup mode to manage APs. The
APs obtain IP addresses and service configurations from the ACs. The BRAS allocates IP
addresses to STAs and works as the gateway for STAs. Data packets from STAs are
forwarded to the active AC through a CAPWAP tunnel and forwarded to the BRAS by the AC
at Layer 2. The BRAS forwards the data packets to the upstream network at Layer 3.
In this networking, the ACs must be configured with the management VLAN of APs, service
VLANs of STAs, and management VLANs of the aggregation switch and access switches
(PoE switches).
Figure 1-2
Networking of dual-link backup in Layer 2 chain networking
AP
AP
BRAS
AC2
AC1
Aggregation switch
Aggregation switch
Access switch
Access switch
Management VLAN of APs, service VLANs of STAs, and management VLANs of
switches are different.
The management VLAN of the APs only needs to be configured on the ACs and downstream
switches, as shown in Figure 1-3. Therefore, no loop will be formed in the VLAN.
