Details
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Improvement
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Resolution: Unresolved
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Minor
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None
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None
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3
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9223372036854775807
Description
Default linux settings for net.ipv4.neigh.default.gc_thresh* may be too low:
net.ipv4.neigh.default.gc_thresh1 = 128 net.ipv4.neigh.default.gc_thresh2 = 512 net.ipv4.neigh.default.gc_thresh3 = 1024
For example, this can cause the garbage collector in the kernel to start deleting entries in the table once the table size exceeds gc_thresh2, leading to unnecessary ARP traffic.
If IP to MAC mappings in the system are permanent, setting a higher gc_thresh1 may also help avoid unnecessary ARP traffic as this is the threshold for when entries start timing out.
In large systems this may cause troubles with evictions, etc.
The memory cost of having larger tables is low, so It is proposed to use the following settings:
net.ipv4.neigh.default.gc_thresh1 = 8192 net.ipv4.neigh.default.gc_thresh2 = 16384 net.ipv4.neigh.default.gc_thresh3 = 32768
The user should be able to make the choice to manage the settings on their own, probably via a module parameter.
Note that there's the similar set of IPv6 parameters to consider.