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#1 2015-12-04 22:42:58

Horizon_Brave
Operating System: Linux-Nettrix
Registered: 2015-10-18
Posts: 1,473

[SOLVED] Constant ARP Requests?

Hey everyone,

So the bit of backstory is:
Running BunsenLabs in VirtualBox
Host Running Win 10


I have a NAT network in virtualbox, as I just need some basic functionality for now. This really isn't a problem, but more of a curiosity. I'm running a background tcpdump and I notice anytime B.L needs to make a request 'outside" (sent to 10.0.2.2 my default virtual router), I see that an ARP request for the MAC of 10.0.2.2 has to be sent. Even a ping, a traceroute, any NTP requests, etc... they all force B.L to ARP out a request for the MAC. Here's a sample:

spawn id exp6 sent <15:44:27.964752 ARP, Request who-has 10.0.2.2 tell 10.0.2.15, length 28\r\n15:44:27.965098 ARP, Reply 10.0.2.2 is-at 52:54:00:12:35:02 (oui Unknown), length 46\r\n>
15:44:27.964752 ARP, Request who-has 10.0.2.2 tell 10.0.2.15, length 28
15:44:27.965098 ARP, Reply 10.0.2.2 is-at 52:54:00:12:35:02 (oui Unknown), length 46

In my tcpdumps these are appearing really really often.

What's interesting though, is that if I look at my arp cache,  the 10.0.2.2 address IS there with the MAC that it gets.  So I'm not sure why B.L needs to keep querying with more ARP's?

Again this isn't a real issue, but it's just a curiosity.

Last edited by Horizon_Brave (2015-12-05 16:39:25)


"I have not failed, I have found 10,000 ways that will not work" -Edison

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#2 2015-12-05 14:20:38

twoion
ほやほや
Registered: 2015-08-10
Posts: 2,482

Re: [SOLVED] Constant ARP Requests?

Hm, maybe play with the ARP cache timeouts?


A silent kite against the blue, blue sky

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#3 2015-12-05 16:05:10

Horizon_Brave
Operating System: Linux-Nettrix
Registered: 2015-10-18
Posts: 1,473

Re: [SOLVED] Constant ARP Requests?

Solved!

The issue (not even an issue) Is that the arp cache isn't flushed all *that* often. (every 300 seconds) This is according to:

cat /proc/sys/net/ipv4/route/gc_timeout 
300

But, the conflict is that even though the arp times out a 300 secs, the state of the neighbor (the 10.0.2.2 virtual switch) switches from reachable to stale only every 60 seconds.

kingghidorah:~$ ip neighbor list
10.0.2.2 dev eth0 lladdr 52:54:00:12:35:02 REACHABLE

kingghidorah:~$ ip neighbor list
10.0.2.2 dev eth0 lladdr 52:54:00:12:35:02 REACHABLE

kingghidorah@kingghidorah:~$ ip neighbor list
10.0.2.2 dev eth0 lladdr 52:54:00:12:35:02 STALE


kingghidorah:~$ cat /proc/sys/net/ipv4/neigh/default/gc_stale_time
60

SO! anyway mystery solved! Hope this will now allow you all to sleep at night and stop the restless nights you've been having cause of this.. big_smile


"I have not failed, I have found 10,000 ways that will not work" -Edison

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#4 2015-12-05 16:32:57

twoion
ほやほや
Registered: 2015-08-10
Posts: 2,482

Re: [SOLVED] Constant ARP Requests?

I thought so smile

Can we mark this as [solved] then? Thanks.


A silent kite against the blue, blue sky

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#5 2015-12-05 16:39:01

Horizon_Brave
Operating System: Linux-Nettrix
Registered: 2015-10-18
Posts: 1,473

Re: [SOLVED] Constant ARP Requests?

Surely... as long as you impart your powers of intuition on me  big_smile


"I have not failed, I have found 10,000 ways that will not work" -Edison

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