This article provides information on how to increase the delay of Gratuitous ARP (GARP) on a SRX device.
GARP is a method of establishing an association between a logical IP address and a hardware address, whenever an interface is created or the state of the interface shifts to the operationally up state. On the other hand, ARP dynamically binds the IP address (the logical address) to the correct MAC address. The device that transmits a GARP populates both the source and destination fields with its own information. The devices that receive the GARP requests might update the ARP caches with the new information that is contained in the GARP packets. By default, the Junos OS sends gratuitous ARP requests, immediately after configuration changes are made on an interface (in relation to the network, the changing of the description of the interface does not impact the network; so GARP is not sent for such configuration changes). This might lead to the Packet Forwarding Engine dropping certain initial request packets, if the configuration updates have not been fully processed. To avoid such request packets from being dropped, you can configure a delay in the Gratuitous ARP requests.
To configure a delay in Gratuitous ARP requests, include the gratuitous-arp-delay seconds statement at the [edit system arp] hierarchy level: Configuration :
root@SRX100-1# show system arp gratuitous-arp-delay 10;
Jan 30 16:49:14 SRX100-1 SRX100-1 IFP trace> ifp_ifa_add_del_event: ifp_ifa_add_del_event: fe-0/0/0, op 1, msg->ifl_index 71, msg->proto 2 Jan 30 16:49:14 SRX100-1 SRX100-1 IFP trace> ifp_ifa_add: ifp_ifa_add : fe-0/0/0, msg->ifl_index 71 local prefix 3232523777/32, dest prefix 3232523776/24 Jan 30 16:49:14 SRX100-1 SRX100-1 IFP trace> ifp_add_addr: ifp_add_addr : insert into addr list fe-0/0/0.0 0x4cc77170 Jan 30 16:49:14 SRX100-1 mgd[6463]: UI_COMMIT_PROGRESS: Commit operation in progress: ssync begins Jan 30 16:49:14 SRX100-1 mgd[6463]: UI_COMMIT_PROGRESS: Commit operation in progress: ssync ends Jan 30 16:49:14 SRX100-1 mgd[6463]: UI_COMMIT_PROGRESS: Commit operation in progress: commit complete
16:49:24.125040 Out 00:26:88:4f:c8:00 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 42: arp who-has 192.172.102.1 tell 192.172.102.1