More on ARP caching...

[Tom Samplonius (tom@uniserve.com)]

  I have some questions about ARP caching works in 2.4.

  According to the manpage, ARP garbage collection does not occur unless there
are "gc_thres1" entries.  But "gc_thres1" is by default 128, and I know on small
networks that ARP entries do age out.  How does the aging of stale entries work
vs. garbage collection?

  "gc_stale_time" is also a little confusing.  The manpage says, "Determines how
often to check for stale neighbour entries", but the other postings that I've
read indicate that "gc_stale_time" is an inactivity timer for ARP entries, not a
scanning interval to look for stale entries.

  I also don't understand what values affect <incomplete> entries.  They seem to
be aged out very quickly.  Do the incomplete entries act as an ARP negative
cache?

  My goal is try to reduce ARP traffic on a Linux box acting as router.  The box
has a number of NIC cards, and number of subnets on each interface.  The ARP
table usually has around 3,800 entries.  I've increased gc_thres1 to 4000,
gc_thres2 to 4500, and gc_thres3 to 5000.  I'm not sure what else I can do.


Tom

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