Re: Gratuitous ARP

"Tom Collins tom-lnEA/wrDJtNWk0Htik3J/[email protected] [rabbit-semi]" <[email protected]> Tue, 9 Jan 2018 15:23:34 -0800
Newsgroups gmane.comp.hardware.rabbit-semiconductor
Message-ID <[email protected]>
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So you don=E2=80=99t see an ARP on the network that the Rabbit might be res=
ponding to.  Does the target MAC vary, or is it always the same?

Are you using DHCP?  If so, could this event be happening around the time o=
f a renewal?

Does the TCP connection go to:
- the default gateway for the network=20
- some other local device
- a remote device (via the default gateway)

Can you enable ARP_VERBOSE for a build, and see what sorts of ARP-related m=
essages it=E2=80=99s spitting out right before failing?  That might give a =
clue as to what=E2=80=99s triggering the ARP request and decision to drop t=
he connection (so TCP_VERBOSE or IP_VERBOSE or NET_VERBOSE might also provi=
de context, but may also require too much space or slow the device down too=
 much).

Feel free to email me directly with detailed information to debug the issue=
..  If there=E2=80=99s a bug in the DC 9.62 TCP/IP stack, I=E2=80=99d like t=
o get it fixed and pushed up to the GitHub repository.

-Tom


> On Jan 9, 2018, at 10:41 AM, Steve Trigero seecwriter-/[email protected] [rabbit-s=
emi] <[email protected]> wrote:
>=20
>=20
> I have an RCM3900 module that has a TCP connection with a host. The modul=
e is receiving TCP packets at about a 1-second rate. So everything is hummi=
ng along with the host sending TCP packets requesting status info, and modu=
le responds with the data.  After a some time, minutes to hours, of running=
, the module issues 2-gratuitous ARP packets, about a second apart. And upo=
n receiving the next TCP packet, the module responds by closing the connect=
ion.
>=20
> Both gratuitous ARP packets have the same ARP data:
>=20
> Opcode: request (1)
> Sender MAC address: 00:90:c2:f7:fd:36
> Sender IP address:      192.168.1.64
> Target MAC address: 3f:c7:01:00:b4:e5
> Target IP address:       192.168.1.64
>=20
> The target MAC doesn't appear to be valid.  According to what I read, an =
opcode of 1 is an ARP Probe or an ARP Announcement. If a probe, the sender =
IP and target MAC are supposed to be set to 0, and the target IP set to the=
 IP in question (to see if it's taken), and if an announcement, the sender =
IP and target IP are set to the same IP and the target MAC is set to 0 to a=
nnounce that this NIC is using this IP address.  The format of the above do=
esn't fit either format.  Could this be indicating an IP conflict?=20=20
> There is no response to either message.
>=20
>=20
>=20
>=20


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      <p>So you don=E2=80=99t see an ARP on the network that the Rabbit mig=
ht be responding to. &nbsp;Does the target MAC vary, or is it always the sa=
me?<div class><br class></div><div class>Are you using DHCP? &nbsp;If so, c=
ould this event be happening around the time of a renewal?</div><div class>=
<br class></div><div class>Does the TCP connection go to:</div><div class>-=
 the default gateway for the network&nbsp;</div><div class>- some other loc=
al device</div><div class>- a remote device (via the default gateway)</div>=
<div class><div class><br class></div><div class>Can you enable ARP_VERBOSE=
 for a build, and see what sorts of ARP-related messages it=E2=80=99s spitt=
ing out right before failing? &nbsp;That might give a clue as to what=E2=80=
=99s triggering the ARP request and decision to drop the connection (so TCP=
_VERBOSE or IP_VERBOSE or NET_VERBOSE might also provide context, but may a=
lso require too much space or slow the device down too much).</div><div cla=
ss><br class></div><div class>Feel free to email me directly with detailed =
information to debug the issue. &nbsp;If there=E2=80=99s a bug in the DC 9.=
62 TCP/IP stack, I=E2=80=99d like to get it fixed and pushed up to the GitH=
ub repository.</div><div class><br class><div class>
<span class=3D"Apple-style-span" style=3D"border-collapse: separate;"><div =
class>-Tom</div><br class=3D"Apple-interchange-newline"></span>

</div>
<br class><div><blockquote type=3D"cite" class><div class>On Jan 9, 2018, a=
t 10:41 AM, Steve Trigero <a href=3D"mailto:seecwriter-/[email protected]" class>see=
cwriter-/[email protected]</a> [rabbit-semi] &lt;<a href=3D"mailto:rabbit-semi@yahoo=
groups.com" class>[email protected]</a>&gt; wrote:</div><br class=
=3D"Apple-interchange-newline"><div class><div id=3D"ygrp-mlmsg" style=3D"f=
ont-size: 13px;font-family: Arial, helvetica, clean, sans-serif;font-style:=
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eorgia;" class><div style=3D"margin: 0px 0px 1em;" class><br class=3D"webki=
t-block-placeholder"></div><div style=3D"font-family: 'times new roman', 'n=
ew york', times, serif;font-size: 16px;" class><div class>I have an RCM3900=
 module that has a TCP connection with a host. The module is receiving TCP =
packets at about a 1-second rate. So everything is humming along with the h=
ost sending TCP packets requesting status info, and module responds with th=
e data.&nbsp; After a&nbsp;some time, minutes to hours, of running, the mod=
ule issues 2-gratuitous ARP packets, about a second apart. And upon receivi=
ng the next TCP packet, the module responds by closing the connection.</div=
><div class><br class></div><div class>Both gratuitous ARP packets have the=
 same ARP data:</div><div class><br class></div><div class>Opcode: request =
(1)</div><div class>Sender MAC address: 00:90:c2:f7:fd:36</div><div class>S=
ender IP address:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 192.168.1.64</div><div clas=
s>Target MAC address: 3f:c7:01:00:b4:e5</div><div class>Target IP address:&=
nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 192.168.1.64</div><div class><br class>=
</div><div class>The target MAC doesn't appear to be valid.&nbsp; According=
 to what I read, an opcode of 1 is an ARP Probe or an ARP Announcement.&nbs=
p;If a probe, the sender IP and target MAC are supposed to be set to 0, and=
 the target IP set to the IP in question (to see if it's taken), and if an =
announcement, the sender IP and target IP are set to the same IP and the ta=
rget MAC is set to 0 to announce that this NIC is using this IP address.&nb=
sp; The format of the above doesn't fit either format.&nbsp;&nbsp;Could thi=
s&nbsp;be indicating an IP conflict?&nbsp;<span class=3D"Apple-converted-sp=
ace">&nbsp;</span></div><div class>There is no response to either message.<=
/div><div class><br class></div><div class><br class></div></div><div style=
=3D"margin: 0px 0px 1em;" class><br class=3D"webkit-block-placeholder"></di=
v></div><div style=3D"color: rgb(255, 255, 255);height: 0px;" class></div><=
/div></div></div></blockquote></div><br class></div></div></p>

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