First packets not being sent - ARP?

Hi!

I have two Linux machines (details below) connected to each other
through Ethernet. Networking seems to be configured properly, I can
access the Internet from both computers and they can communicate with
each-other.

However- I noticed that sometimes the "first" few packets of a message
are not being send (or not being received) correctly, when sending
messages betwen my 2 computers.

It took me a while to realize what "first" means, because I had trouble
even reproducing the error. It sometimes happens after booting, when
first trying to send to a specific IP. Say the IP of one machine is
130.60.50.2 and the other 130.60.50.3.

Writing "arp -d 130.60.50.3" on the 130.60.50.2 causes the next packets
sent from 130.60.50.2 (the number of which seems to go from 1 to 7, at
random) to get lost, and then the rest of the packets are normal...

So it seems ARP is somehow not being called correctly, and that packets
try to get through before the ARP replies arrive.

Any ideas? Has anyone seen this kind of problem elsewhere?

Here are some details:
*Both machines are running Linux Kernel 2.4.20, Redhat 9.

*Each machine has TWO network cards- one set is connected to a network,
and the other set is connected through cross-cable.

*I have, admittedly, been messing around with the Kernel code changing
all sorts of stuff about packets. However, I never modified the original
version of the kernel; the problem I described happens in the
UN-MODIFIED kernel as well (I have verified that the unmodified version
really doesn't run the code I wrote in my own kernel).

Thanks in advance,
Daniel

On Sat, 01 Nov 2003 10:36:21 +0300, Daniel <(E-Mail Removed)> wrote:
> Hi!
>
> I have two Linux machines (details below) connected to each other
> through Ethernet. Networking seems to be configured properly, I can
> access the Internet from both computers and they can communicate with
> each-other.
>
> However- I noticed that sometimes the "first" few packets of a message
> are not being send (or not being received) correctly, when sending
> messages betwen my 2 computers.
>
> It took me a while to realize what "first" means, because I had trouble
> even reproducing the error. It sometimes happens after booting, when
> first trying to send to a specific IP. Say the IP of one machine is
> 130.60.50.2 and the other 130.60.50.3.
>
> Writing "arp -d 130.60.50.3" on the 130.60.50.2 causes the next packets
> sent from 130.60.50.2 (the number of which seems to go from 1 to 7, at
> random) to get lost, and then the rest of the packets are normal...
>
> So it seems ARP is somehow not being called correctly, and that packets
> try to get through before the ARP replies arrive.
>
> Any ideas? Has anyone seen this kind of problem elsewhere?
>
> Here are some details:
> *Both machines are running Linux Kernel 2.4.20, Redhat 9.
>
> *Each machine has TWO network cards- one set is connected to a network,
> and the other set is connected through cross-cable.

Sounds like you have a routing problem with dual connections between the
boxes (arp replies coming back from both or wrong interface). But
impossible to tell anything specific without knowing IP/netmask set for
each interface and output of route -n, for each box.

--
David Efflandt - All spam ignored http://www.de-srv.com/
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"Daniel" <(E-Mail Removed)> wrote in message news:(E-Mail Removed)...
> Hi!
>
> I have two Linux machines (details below) connected to each other
> through Ethernet. Networking seems to be configured properly, I can
> access the Internet from both computers and they can communicate with
> each-other.
>
>
> Any ideas? Has anyone seen this kind of problem elsewhere?
>
> Here are some details:
> *Both machines are running Linux Kernel 2.4.20, Redhat 9.
>
> *Each machine has TWO network cards- one set is connected to a network,
> and the other set is connected through cross-cable.


Please list the results from both hosts of 'ifconfig -a' and 'route -n'. If
there are active firewalls, post also the results from 'iptables -nLv'.

Check that the interfaces in the same host are *not* part of the same
subnet, or you'll have routing problems (unless the advanced routing
preparations are taken).

Tauno Voipio
tauno voipio @ iki fi

Thank you for your responses- I appreciate the help.

I'll post the details you suggested tomorrow (because I'll be able to
access the machines then).

From what I remember about the ifconfig output and the routing tables-
everything seemed to be in order, but tomorrow I'll check it again and
post the results.

I think there is a firewall active, perhaps it's causing trouble.

Daniel

Hi,

Well, now I can't seem to reproduce the error, so maybe it got fixed
somehow. There was some technician hanging around that machine, maybe he
corrected the problem.

The machine details in case you can still find a problem with them:

MACHINE A

ifconfig -a:
eth0 Link encap:Ethernet HWaddr 00:0B:CD:96:B5:6E
inet addr:132.68.52.151 Bcast:132.68.52.255
Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1153 errors:0 dropped:0 overruns:0 frame:0
TX packets:541 errors:0 dropped:0 overruns:0 carrier:0
collisions:0
RX bytes:137359 (134.1 Kb) TX bytes:61113 (59.6 Kb)

eth1 Link encap:Ethernet HWaddr 00:02:44:17:09:87
inet addr:192.168.1.1 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:9 errors:0 dropped:0 overruns:0 frame:0
TX packets:9 errors:0 dropped:0 overruns:0 carrier:0
collisions:0
RX bytes:554 (554.0 b) TX bytes:554 (554.0 b)

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:62 errors:0 dropped:0 overruns:0 frame:0
TX packets:62 errors:0 dropped:0 overruns:0 carrier:0
collisions:0
RX bytes:4416 (4.3 Kb) TX bytes:4416 (4.3 Kb)




route -n:
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use
Iface
132.68.52.0 0.0.0.0 255.255.255.0 U 0 0 eth0
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0
eth1
169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0
eth1
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0
lo
0.0.0.0 132.68.52.254 0.0.0.0 UG 0 0 0
eth0


arp:
Address HWtype HWaddress Flags Mask
Iface
132.68.52.64 ether 08:00:202:54:9F C
eth0
192.168.1.2 ether 00:02:44:17:09:88 C
eth1
132.68.52.254 ether 00:08:209:2C:7C C
eth0
132.68.52.150 ether 00:0B:CD:98:22C C
eth0


iptables -nLv:
iptables: Table does not exist (do you need to insmod?)




************************************************** ************************

MACHINE B


ifconfig -a:

eth0 Link encap:Ethernet HWaddr 00:0B:CD:98:22C
inet addr:132.68.52.150 Bcast:132.68.52.255
Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1080 errors:0 dropped:0 overruns:0 frame:0
TX packets:459 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:101626 (99.2 Kb) TX bytes:49057 (47.9 Kb)
Interrupt:5 Base address:0x1400 Memory:fc500000-fc500038

eth1 Link encap:Ethernet HWaddr 00:02:44:17:09:88
inet addr:192.168.1.2 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:5 errors:0 dropped:0 overruns:0 frame:0
TX packets:9 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:314 (314.0 b) TX bytes:554 (554.0 b)
Interrupt:10 Base address:0xc000

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:2436 errors:0 dropped:0 overruns:0 frame:0
TX packets:2436 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:166242 (162.3 Kb) TX bytes:166242 (162.3 Kb)



route -n:

Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use
Iface
132.68.52.0 0.0.0.0 255.255.255.0 U 0 0 0
eth0
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0
eth1
169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0
eth1
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0
lo
0.0.0.0 132.68.52.254 0.0.0.0 UG 0 0 0
eth0



arp:

Address HWtype HWaddress Flags Mask
Iface
132.68.52.64 ether 08:00:202:54:9F C
eth0
192.168.1.1 ether 00:02:44:17:09:87 C
eth1
132.68.52.254 ether 00:08:209:2C:7C C
eth0
132.68.52.151 ether 00:0B:CD:96:B5:6E C
eth0



iptables -nLv:

iptables: Table does not exist (do you need to insmod?)




Thanks for the help,
Daniel