Adjusting Aging Parameters of Dynamic ARP Entries
Properly adjusting aging parameters of dynamic ARP entries can improve network reliability. Aging and updating of dynamic ARP entries will be affected if the device is enabled to perform Layer 2 topology detection, respond to TC BPDUs, or delete dynamic ARP entries after a delay.
Context
Aging time of dynamic ARP entries: the aging time of a dynamic ARP entry is reached, the device sends an ARP Request packet to the mapping outbound interface and starts ARP aging probing. If the aging time is too short (for example, 1 minute), the device consumes most resources on updating dynamic ARP entries and cannot process other services. If the aging time is too long (for example, 15 hours), the device may not update dynamic ARP entries in a timely manner. The default aging time (20 minutes) is recommended.
Number of aging probes to dynamic ARP entries: Before aging a dynamic ARP entry, the device sends probes to detect status of the entry. If the device receives no response for updating the entry after the specified number of probes, the device deletes the ARP entry.
Aging detection mode of dynamic ARP entries: Before an ARP entry is aged, an interface sends an ARP aging probe packet.
- If the IP address of the peer device remains the same but the MAC address changes frequently, it is recommended that you configure ARP aging probe packets to be broadcast.
- If the MAC address of the peer device remains the same, and the network bandwidth is insufficient, it is recommended that you configure ARP aging probe packets to be unicast.
Aging and updating of dynamic ARP entries is also affected if the device is enabled to perform Layer 2 topology detection, respond to TC BPDUs, or delete dynamic ARP entries after a delay.
Procedure
- Adjusting aging parameters of dynamic ARP entries
- Run system-view
The system view is displayed.
- Run interface interface-type interface-number
The interface view is displayed.
- Run arp expire-time expire-time
The aging time of dynamic ARP entries is set.
By default, the aging time of dynamic ARP entries is 1200 seconds, that is, 20 minutes.
- Run arp detect-times detect-times
The number of probes to dynamic ARP entries is set.
By default, the number of ARP probes is 3.
- Run arp detect-mode unicast
An interface is configured to send ARP aging probe packets in unicast mode.
By default, an interface sends the last ARP Aging Detection packet in broadcast mode, and the rest ARP Aging Detection packets are sent in unicast mode.
- Run system-view
- Configuring the functions that affect dynamic ARP entry update (in special scenarios)
Enabling Layer 2 topology detection
If no STP protocol is configured on a ring network (for example, STP is not required if the device can determine the master and backup links), Layer 2 topology detection can be enabled to ensure real-time update of dynamic ARP entries.
Layer 2 topology detection enables the system to update all the ARP entries in the VLAN that a Layer 2 interface belongs to when the Layer 2 interface status changes from Down to Up.
Run system-view
The system view is displayed.
Run l2-topology detect enable
Layer 2 topology detection is enabled.
By default, Layer 2 topology detection is disabled.