setting gc_stale_time does not decrease ARP requests

psycroptic · 10-27-2013, 12:36 PM

in trying to reduce the frequency of ARPs sent from my router to modem, I would think setting gc_stale_time on the interface to a higher number would do it - 600 in this case for 10 mins. But I still have ARPs sent a few times every minute:

Code:

11:24:12.509865 ARP, Request who-has y.y.y.y tell x.x.x.x, length 28
11:24:12.510246 ARP, Reply y.y.y.y is-at b8:9b:c9:d9:a8:4a, length 46
11:24:54.456558 ARP, Request who-has y.y.y.y tell x.x.x.x, length 28
11:24:54.456919 ARP, Reply y.y.y.y is-at b8:9b:c9:d9:a8:4a, length 46
11:25:35.563199 ARP, Request who-has y.y.y.y tell x.x.x.x, length 28
11:25:35.563559 ARP, Reply y.y.y.y is-at b8:9b:c9:d9:a8:4a, length 46
11:26:15.229867 ARP, Request who-has y.y.y.y tell x.x.x.x, length 28
11:26:15.230238 ARP, Reply y.y.y.y is-at b8:9b:c9:d9:a8:4a, length 46
11:26:55.096522 ARP, Request who-has y.y.y.y tell x.x.x.x, length 28
11:26:55.096885 ARP, Reply y.y.y.y is-at b8:9b:c9:d9:a8:4a, length 46

is there some other reason for these requests to be sent?

nini09 · 10-29-2013, 03:23 PM

It is complex to control ARP request interval. You can try change gc_stale_time and gc_interval under neigh and route directory.

baldy3105 · 10-30-2013, 01:47 PM

Whats the point? Is it causing a problem?

psycroptic · 10-30-2013, 10:22 PM

just trying to minimize unnecessary network traffic.

it actually did work after some time, although the cable modem it was connected to eventually lost access, after which changing it back to the default resumed normal operation. it's not a big deal.

baldy3105 · 11-03-2013, 12:46 PM

I've not seen an issue with normal ARP operation since we left the era of huge flat bridged networks behind (and good riddance!).
My rule of thumb, painfully learned over 25 years is, if it ain't broke don't fix it :-)

I KNOW, I think its Heinlein who talked about how people only ever learn the hard way......thats me...

psycroptic · 11-03-2013, 12:52 PM

me as well

but thats the best way to learn.

actually somewhat interestingly, one time i set up a packet counter at my parents house (residential cable modem) on the linux router there, filtering for ARP packets, and left it running for ~2 weeks. the amount of data used by ARP traffic alone was >11GB! literally 50-100 arps a second.

baldy3105 · 11-04-2013, 04:21 AM

Ouch, that's NOT normal!

psycroptic · 11-04-2013, 06:59 PM

yeah, nearly all of them are "tell x.x.x.1", i'm assuming coming from comcast's routers. to top it all off, that 11GB most definitely counts towards the bandwidth cap, even though it's completely un-initiated from the user.