Description

There can be packet drops in IP fabric with CRB (central routing bridging) model. With CRB overlay model L3 gateway is configured on the Spine devices while Leaf devices function on L2 level only. Due to ARP expiration on the Spine devices the transit packets can be dropped on the Spine device. This happenes because by default QFX device does not refresh ARP entry before the ARP entry got expired. After the ARP entry expired, QFX Spine device in CRB mode is triggered to send ARP request by the traffic. There will be packet drops until the new ARP entry is installed.

Solution

The solution to avoid packet drops in the described scenario depends on the Spine device:
1. If the Spine device is running Junos, the recommended solution is to configure 'proxy-macip-advertisement' feature, for example:
  
[edit interfaces irb unit logical-unit-number ]
    proxy-macip-advertisement
With this configuration the Spine device sends ARP Request message before ARP entry got expired. This configuration is not supported on Junos EVO.

2. If the Spine device is running Junos EVO, the following configuration has to be enabled on the leaf devices  (which are running Junos or Junos EVO):
  
set protocols l2-learning crb-proxy-mac family inet <MAC address>
set protocols l2-learning crb-proxy-mac family inet6 <MAC address>
With crb-proxy-mac command leaf devices are responsible to refresh ARP entries using the configured MAC address. Here MAC address can be any unused MAC address. After leaf device receives ARP reply, it sends BGP EVPN type 2 route towards the Spine so the ARP knowledge can be refreshed on the Spine device.
 

Modification History

2024-06-21 : Article Created