[solved] ARP probing, or: Why is dhcpcd wasting my time?

md2k7 · 2012-01-15 12:29:21

Hello,

I've been wondering why setting up a wireless connection takes so long, especially with DHCP. I've looked into the logs and was stunned to find this in /var/log/daemon.log:

Jan 15 12:08:43 localhost dhcpcd[8242]: wlan0: checking for 192.168.1.80
Jan 15 12:08:48 localhost dhcpcd[8242]: wlan0: leased 192.168.1.80 for 43200 seconds

What actually happens in these 5-6 seconds, according to the dhcpcd source code, is that "ARP probes" are being sent out to query for the address that is about to be taken. But this address was assigned to me by my router, so it's not probable at all that this address *is* actually taken.

For me, this means dhcpcd is wasting a full 5 seconds of my life every time I connect to a DHCP network! Okay, now that's really worth a forum post ;-)

No, seriously, if users connect to a network, they usually want to do stuff and not wait for the improbable case that the network is not configured correctly and someone has the same IP address.

Summary: I don't see any usecases for this "feature" except for stealing users' time. Any comments?

Yours
David

Last edited by md2k7 (2012-01-16 11:09:25)

hexanol · 2012-01-15 13:48:28

It does so because that's part of RFC2131, section 2.2. A recommended part, that is.

I agree this is mostly useless on small networks like home networks, where network configuration tends to be quite simple.

Last edited by hexanol (2012-01-15 13:49:34)

brebs · 2012-01-15 14:02:00

Use --noarp

md2k7 · 2012-01-15 14:51:25

brebs wrote:

Use --noarp

Oh that's funny, should've read the manpage first - nevermind

I use NetworkManager which then starts dhcpcd, so I've put "noarp" in /etc/dhcpcd.conf. Works fine, thanks

Yours
David

Arch Linux

#1 2012-01-15 12:29:21

[solved] ARP probing, or: Why is dhcpcd wasting my time?

#2 2012-01-15 13:48:28

Re: [solved] ARP probing, or: Why is dhcpcd wasting my time?

#3 2012-01-15 14:02:00

Re: [solved] ARP probing, or: Why is dhcpcd wasting my time?

#4 2012-01-15 14:51:25

Re: [solved] ARP probing, or: Why is dhcpcd wasting my time?

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