Reporting Topology Changes in a Lower-Layer Network - SEP Topology Change Notification
Context
SEP runs on devices at the access layer. The topology change notification function enables devices to detect topology changes on the upper and lower-layer networks.
If the upper-layer network fails to be notified of the topology change in a SEP segment, the MAC address entries remain unchanged on the upper layer network and user traffic may be interrupted. To ensure uninterrupted traffic forwarding, configure devices on the lower-layer network to report topology changes to the upper-layer network and specify the devices on the upper-layer network that will be notified of topology changes.
Currently, topology changes in a SEP segment can be reported to other SEP segments, STP networks, RRPP networks, VPLS networks, and SmartLink networks.
Only S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731S-H, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730S-H, and S6730-H support VPLS networks.
After receiving a topology change notification from a lower-layer network, a device on the upper-layer network sends TC packets to instruct other devices on the upper-layer network to clear original MAC addresses and learn new MAC addresses after the topology of the lower-layer network changes. This ensures uninterrupted traffic forwarding.
Procedure
- Run system-view
The system view is displayed.
- Run sep segment segment-id
A SEP segment is created and the view of the SEP segment is displayed.
- Run tc-notify { segment { segment-id1 [ to segment-id2 ] } &<1-10> | stp | rrpp | smart-link send-packet vlan vlan-id | vpls }
The topology change of the specified SEP segment is reported to another SEP segment or a network running other ring protocols such as STP or RRPP.
By default, the topology change of a SEP segment is not reported.
Only S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731S-H, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730S-H, and S6730-H support vpls parameter.
Follow-up Procedure
In the networking scenario where three or more SEP ring networks exist, when a topology change notification is sent through multiple links, the upper-layer network will receive it multiple times. This reduces packet processing efficiency on the upper-layer network. Therefore, topology change notifications need to be suppressed. Suppressing topology change notifications frees the upper-layer network from processing multiple duplicate packets and protects the devices in the SEP segment against topology change notification attacks.
Run the tc-protection interval interval-value command in the SEP segment view to set the interval for suppressing topology change notifications.
By default, the interval for suppressing topology change notifications is 2s, and three topology change notifications with different source addresses are processed within 2s.
In the networking scenario where three or more SEP ring networks exist, the tc-protection interval interval-value command must be run. If this command is not run, the default interval for suppressing topology change notifications is used.
A longer interval ensures stable SEP operation but reduces convergence performance.