How to set an interval for sending LBDT packets on an S series switches and how to distinguish LBDT packets sent by different interfaces

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S series (except the S1700) and E series switches send LBDT packets in the following modes:
1. For fixed switches in V100R005
- An LBDT packet is sent every 100 ms. You can run the loopback-detect interval interval-time command to set an interval for sending LBDT packets. In the command, the value of interval-time ranges from 5 to 300, in seconds. By default, the interval for sending LBDT packets is 30s.

- LBDT packets sent by different interfaces are distinguished based on protocol IDs carried in the packets. By default, the protocol ID of interface 1 on the S3700 is 0x606 and the protocol IDs of the other interfaces are incremented. You can run the loopback-detect protocol protocol-id command to manually set a protocol ID. Note that the protocol ID cannot be the same as an existing protocol ID. For details, see the command reference.
2. For fixed switches in V100R006 and later versions, modular switches, and E series switches

- An LBDT packet is sent every 5s. You can run the loopback-detect packet-interval packet-interval-time command to set an interval for sending LBDT packets. The value of packet-interval-time ranges from 1 to 300, in seconds.
- LBDT packets sent by different interfaces are distinguished based on interface indexes carried in the packets.

Note: LBDT packets are sent frequently. Therefore, the CPU usage will increase if the LBDT function is enabled on all interfaces.

Other related questions:
Can protocol packets be sent if an interface with a loop detected is blocked on an S series switches
Can protocol packets be sent if an interface with a loop detected is blocked on an S series (except the S1700) or E series switch? For S series switches (except the S1700), the destination MAC address of LDT packets and tagged LBDT packets is all Fs. These packets cannot be sent through an interface if it is blocked. The destination MAC address of untagged LBDT packets is a BPDU MAC address. These packets can still be sent through an interface even if it is blocked. For E series switches, the destination MAC address of tagged LBDT packets is all Fs. These packets cannot be sent through an interface if it is blocked. The destination MAC address of untagged LBDT packets is a BPDU MAC address. These packets can still be sent through an interface even if it is blocked.

What is LBDT and what are the differences between LBDT and LDT
Loopback detection (LBDT) is different from loop detection (LDT) in the following aspects: 1. Application scenario: LBDT is applied on edge switches to prevent switch port fiber loopback or loopback of downstream loops to the port. LDT is applied on aggregation switches to detect loopbacks and loops on the entire Layer 2 network. 2. Configuration modes: LBDT is configured based on port modes. LDT is configured based on system modes. 3. Configuration command: LBDT configuration command: loopback-detect enable. This command is used to enable loopback detection for ports. LDT configuration command: loop-detection enable. Example: loop-detection enable vlan 200. This LDT configuration command is used to enable the VLAN-based loop detection function.

How are VRRP packets of an S series switch sent in a super-VLAN
For S series switches (except the S1700), you are not advised to create a VRRP group on the corresponding VLANIF interface for a super-VLAN. If such a VRRP group has been created, the total number of VLANs (including common VLANs, super-VLANs, and sub-VLANs) in the VRRP group cannot exceed 256 to minimize impact on host performance. By default, if a VRRP group is configured for a super-VLAN, the master switch sends VRRP Advertisement packets to the super-VLAN's sub-VLAN that is in Up state and has the smallest VLAN ID among all the sub-VLANs. You can run a related command to configure VRRP Advertisement packets to be sent in a specified sub-VLAN. This prevents VRRP Advertisement packets from being broadcast in all sub-VLANs, reducing network bandwidth consumption. The configuration procedure is as follows: 1. Run the system-view command to enter the system view. 2. Run the interface vlanif vlan-id command to enter the VLANIF interface view. 3. Run the vrrp advertise send-mode { sub-vlan-id | all } command to configure a mode in which the master switch sends VRRP Advertisement packets in a super-VLAN. - sub-vlan-id: specifies the ID of a sub-VLAN where the master switch sends VRRP Advertisement packets. - all: indicates that the master switch sends VRRP Advertisement packets to all sub-VLANs in a super-VLAN. Note: The parameter all is not recommended. If all is configured, a super-VLAN broadcasts a VRRP Advertisement packet to all its sub-VLANs, which increases bandwidth usage.

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