Date: Mon, 11 Jun 2012 17:52:51 +0200 From: Monthadar Al Jaberi <monthadar@gmail.com> To: freebsd-wireless@freebsd.org Subject: AP <-> STA: tcpdump shows duplicate ARP request from STA, but STA only sends one. Message-ID: <CA%2BsBSo%2BKF-OABC8v=3hPfn433Lhi2wkcP3Q%2B5Hu9H%2BHnpC2kGw@mail.gmail.com>
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Hi,
I am looking at tcpdump output from an AP <-> STA setup with ping.
Running FreeBSD Current @ RSPRO with XR-2 wifi card (pciconf says:
AR5413 802.11abg NIC).
AP setup:
ifconfig wlan0 create wlandev ath0 wlanmode hostap mode 11g channel 7
ssid 3a3a -bgscan
tcpdump -i wlan0 -XXX &
ifconfig wlan0 inet 192.168.0.1
STA setup:
ifconfig wlan0 create wlandev ath0 wlanmode sta mode 11g channel 7
ssid 3a3a -bgscan
tcpdump -i wlan0 -XXX &
ifconfig wlan0 inet 192.168.0.2
I setup AP first, then STA. tcpdump output:
After AP setup on AP:
17:40:22.373042 ARP, Request who-has 192.168.0.1 tell 192.168.0.1, length 28
0x0000: ffff ffff ffff 0015 6d67 2173 0806 0001 ........mg!s....
0x0010: 0800 0604 0001 0015 6d67 2173 c0a8 0001 ........mg!s....
0x0020: 0000 0000 0000 c0a8 0001 ..........
After STA setup on STA:
01:04:08.778887 ARP, Request who-has 192.168.0.2 tell 192.168.0.2, length 28
0x0000: ffff ffff ffff 0015 6d67 2194 0806 0001 ........mg!.....
0x0010: 0800 0604 0001 0015 6d67 2194 c0a8 0002 ........mg!.....
0x0020: 0000 0000 0000 c0a8 0002 ..........
After STA setup on AP:
17:40:40.814970 00:15:6d:67:21:94 (oui Unknown) > Broadcast Null
Supervisory, Receiver not Ready, rcv seq 64, Flags [Poll], length 6
0x0000: ffff ffff ffff 0015 6d67 2194 0006 0000 ........mg!.....
0x0010: f581 8000 ....
17:40:40.815023 00:15:6d:67:21:94 (oui Unknown) > Broadcast Null
Supervisory, Receiver not Ready, rcv seq 64, Flags [Poll], length 6
0x0000: ffff ffff ffff 0015 6d67 2194 0006 0000 ........mg!.....
0x0010: f581 8000 ....
17:40:40.816963 ARP, Request who-has 192.168.0.2 tell 192.168.0.2, length 28
0x0000: ffff ffff ffff 0015 6d67 2194 0806 0001 ........mg!.....
0x0010: 0800 0604 0001 0015 6d67 2194 c0a8 0002 ........mg!.....
0x0020: 0000 0000 0000 c0a8 0002 ..........
17:40:40.817024 ARP, Request who-has 192.168.0.2 tell 192.168.0.2, length 28
0x0000: ffff ffff ffff 0015 6d67 2194 0806 0001 ........mg!.....
0x0010: 0800 0604 0001 0015 6d67 2194 c0a8 0002 ........mg!.....
0x0020: 0000 0000 0000 c0a8 0002 ..........
Now I run ping -c 1 192.168.0.1.
After 'ping -c 1 192.168.0.1' from STA on STA:
01:04:25.769500 ARP, Request who-has 192.168.0.1 tell 192.168.0.2, length 28
0x0000: ffff ffff ffff 0015 6d67 2194 0806 0001 ........mg!.....
0x0010: 0800 0604 0001 0015 6d67 2194 c0a8 0002 ........mg!.....
0x0020: 0000 0000 0000 c0a8 0001 ..........
01:04:25.776037 ARP, Reply 192.168.0.1 is-at 00:15:6d:67:21:73 (oui
Unknown), length 28
0x0000: 0015 6d67 2194 0015 6d67 2173 0806 0001 ..mg!...mg!s....
0x0010: 0800 0604 0002 0015 6d67 2173 c0a8 0001 ........mg!s....
0x0020: 0015 6d67 2194 c0a8 0002 ..mg!.....
01:04:25.776097 IP 192.168.0.2 > 192.168.0.1: ICMP echo request, id
1330, seq 0, length 64
0x0000: 0015 6d67 2173 0015 6d67 2194 0800 4500 ..mg!s..mg!...E.
0x0010: 0054 20c5 0000 4001 d890 c0a8 0002 c0a8 .T....@.........
0x0020: 0001 0800 4d0b 0532 0000 0000 0109 000b ....M..2........
0x0030: b9ab 0809 0a0b 0c0d 0e0f 1011 1213 1415 ................
0x0040: 1617 1819 1a1b 1c1d 1e1f 2021 2223 2425 ...........!"#$%
0x0050: 2627 2829 2a2b 2c2d 2e2f 3031 3233 3435 &'()*+,-./012345
0x0060: 3637 67
01:04:25.777758 IP 192.168.0.1 > 192.168.0.2: ICMP echo reply, id
1330, seq 0, length 64
0x0000: 0015 6d67 2194 0015 6d67 2173 0800 4500 ..mg!...mg!s..E.
0x0010: 0054 22b0 0000 4001 d6a5 c0a8 0001 c0a8 .T"...@.........
0x0020: 0002 0000 550b 0532 0000 0000 0109 000b ....U..2........
0x0030: b9ab 0809 0a0b 0c0d 0e0f 1011 1213 1415 ................
0x0040: 1617 1819 1a1b 1c1d 1e1f 2021 2223 2425 ...........!"#$%
0x0050: 2627 2829 2a2b 2c2d 2e2f 3031 3233 3435 &'()*+,-./012345
0x0060: 3637 67
After 'ping -c 1 192.168.0.1' from STA on AP:
17:40:57.809311 ARP, Request who-has 192.168.0.1 tell 192.168.0.2, length 28
0x0000: ffff ffff ffff 0015 6d67 2194 0806 0001 ........mg!.....
0x0010: 0800 0604 0001 0015 6d67 2194 c0a8 0002 ........mg!.....
0x0020: 0000 0000 0000 c0a8 0001 ..........
17:40:57.809378 ARP, Request who-has 192.168.0.1 tell 192.168.0.2, length 28
0x0000: ffff ffff ffff 0015 6d67 2194 0806 0001 ........mg!.....
0x0010: 0800 0604 0001 0015 6d67 2194 c0a8 0002 ........mg!.....
0x0020: 0000 0000 0000 c0a8 0001 ..........
17:40:57.809480 ARP, Reply 192.168.0.1 is-at 00:15:6d:67:21:73 (oui
Unknown), length 28
0x0000: 0015 6d67 2194 0015 6d67 2173 0806 0001 ..mg!...mg!s....
0x0010: 0800 0604 0002 0015 6d67 2173 c0a8 0001 ........mg!s....
0x0020: 0015 6d67 2194 c0a8 0002 ..mg!.....
17:40:57.814066 IP 192.168.0.2 > 192.168.0.1: ICMP echo request, id
1330, seq 0, length 64
0x0000: 0015 6d67 2173 0015 6d67 2194 0800 4500 ..mg!s..mg!...E.
0x0010: 0054 20c5 0000 4001 d890 c0a8 0002 c0a8 .T....@.........
0x0020: 0001 0800 4d0b 0532 0000 0000 0109 000b ....M..2........
0x0030: b9ab 0809 0a0b 0c0d 0e0f 1011 1213 1415 ................
0x0040: 1617 1819 1a1b 1c1d 1e1f 2021 2223 2425 ...........!"#$%
0x0050: 2627 2829 2a2b 2c2d 2e2f 3031 3233 3435 &'()*+,-./012345
0x0060: 3637 67
17:40:57.814132 IP 192.168.0.1 > 192.168.0.2: ICMP echo reply, id
1330, seq 0, length 64
0x0000: 0015 6d67 2194 0015 6d67 2173 0800 4500 ..mg!...mg!s..E.
0x0010: 0054 22b0 0000 4001 d6a5 c0a8 0001 c0a8 .T"...@.........
0x0020: 0002 0000 550b 0532 0000 0000 0109 000b ....U..2........
0x0030: b9ab 0809 0a0b 0c0d 0e0f 1011 1213 1415 ................
0x0040: 1617 1819 1a1b 1c1d 1e1f 2021 2223 2425 ...........!"#$%
0x0050: 2627 2829 2a2b 2c2d 2e2f 3031 3233 3435 &'()*+,-./012345
0x0060: 3637 67
I have a couple of questions:
1) What is and why do STA send out 'Broadcast Null Supervisory,
Receiver not Ready'? What I could understand is that this means STA is
not ready to receive data? Why?
2) STA sends one ARP request, but on AP tcpdump shows it as two why?
Same goes for 'Broadcast Null Supervisory, Receiver not Ready' I
guess? Because AP sees two. Why?
I dont think it the retry thing, cause I setup an extra RSPRO as
monitor and it registers only one ARP request.
This could be a question for net people, but I am unsure, and since I
am testing on wifi cards I thought I start here :)
Thnx!
--
Monthadar Al Jaberi
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