Date: Wed, 19 Nov 2025 18:43:13 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 291100] Reduce ARP cache time from 20 minutes to 60 seconds Message-ID: <bug-291100-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=291100 Bug ID: 291100 Summary: Reduce ARP cache time from 20 minutes to 60 seconds Product: Base System Version: Unspecified Hardware: Any OS: Any Status: New Severity: Affects Some People Priority: --- Component: misc Assignee: bugs@FreeBSD.org Reporter: achillesgaikwad@gmail.com Created attachment 265511 --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=265511&action=edit patch to change arp time from 1200s to 60s This patch reduces the default ARP cache timeout (arpt_keep) from 1200 seconds (20 minutes) to 60 seconds to improve network responsiveness in dynamic environments, particularly cloud deployments. ## issue: The current 20-minute ARP cache timeout, while appropriate for traditional stable network environments (Like on-prem systems), causes connectivity issues in modern cloud environments. It is not common that in on prem the IP pool gets recycled quickly within 20 minutes. Where as in cloud environments - 1. Short-lived instances: Client systems may operate for less than 20 minutes before termination, the IP address that the virtual machines held will be reused by other virtual machines. 2. Due to [1] when IP addresses are quickly reassigned to new virtual machines, the OS continues attempting to communicate with the cached (now stale) MAC address instead of performing a fresh ARP resolution until 20 minutes. ## How are we solving this problem?: The patch modifies sys/netinet/if_ether.c by changing the arpt_keep variable initialization: - Before: VNET_DEFINE_STATIC(int, arpt_keep) = (20*60); (1200 seconds) - After: VNET_DEFINE_STATIC(int, arpt_keep) = 60; (60 seconds) ## Rationale: - Better suited for dynamic cloud environments with frequent IP recycling - Better out of the box experience for users, as users do not have to debug and edit sysctl in their environment ## Downsides: - More ARP traffic but this is not going to affect CPU cycles or affect performance of OS in anyway. I hope! ## Is anyone else doing this already? - Yes, Linux has a default ARP cache time of 60 seconds. I tried to find issues that could happen due to arp cache time of 60 seconds but found nothing. ## Request: Please accept my patch where I make this modification for better out of the box experience for users. -- You are receiving this mail because: You are the assignee for the bug.home | help
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