Problem pinging a device from a ubuntu 10.10 server

Hi Experts,
Here's the problem,
I got Nagios3.2.1 installed on ubuntu server 10.10
I have 2 devices that over time,  seems to be down (I use ping test at 10 minutes frequency)
if I do a manual ping from the server to the devices the packet are sent but never received.
if I use my pc for example and ping that very same device, the device reply to my pc.
both pc and servers are on same networks.

is there somewhere in ubuntu that when multiple packet are invalid from a device that it prevents communication with the device?

after an electrical maintenance the camera and the server were shut down and restarted,
the 2 devices that were doing the problem was working properly for about 1 month.
and now I have the very same problem.

if there is a manual way to un ban the device.
if any one can give me at least leads.

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Try to ping, then do the following commands and post an ouput of each of them here.

ip addr show

ip route show

ping x.x.x.x

arp -an
RogerMoquinAuthor Commented:
here's what happening on nagios3 server

localadmin@monitorsvr:~$ ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet scope host lo
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:50:56:12:4d:c6 brd ff:ff:ff:ff:ff:ff
    inet brd scope global eth0
    inet6 fe80::250:56ff:fe12:4dc6/64 scope link
       valid_lft forever preferred_lft forever
localadmin@monitorsvr:~$ ip route show dev eth0  proto kernel  scope link  src
default via dev eth0  metric 100

localadmin@monitorsvr:~$ ping
PING ( 56(84) bytes of data.

--- ping statistics ---
448 packets transmitted, 0 received, 100% packet loss, time 447714ms

localadmin@monitorsvr:~$ arp -an
? ( at 00:00:bc:c4:a4:35 [ether] on eth0
? ( at 00:09:6b:83:44:88 [ether] on eth0
? ( at 00:00:bc:64:a4:a9 [ether] on eth0
? ( at 00:50:56:19:06:aa [ether] on eth0
? ( at 00:80:45:4b:97:0c [ether] on eth0
? ( at 00:50:56:2d:0b:69 [ether] on eth0
? ( at 00:00:bc:c5:21:d7 [ether] on eth0
? ( at 00:00:bc:c5:3f:ff [ether] on eth0
? ( at 00:00:bc:66:84:b2 [ether] on eth0
? ( at 00:00:bc:64:55:87 [ether] on eth0
? ( at 00:17:c5:2a:88:60 [ether] on eth0
? ( at 00:23:ae:c7:95:f0 [ether] on eth0
? ( at 00:00:bc:c4:3e:56 [ether] on eth0
? ( at 00:50:56:2d:88:94 [ether] on eth0
? ( at 00:22:15:35:45:a7 [ether] on eth0
? ( at 00:00:bc:c4:27:f3 [ether] on eth0
? ( at 00:00:bc:c5:1d:df [ether] on eth0
? ( at 00:00:bc:64:8c:0f [ether] on eth0
? ( at 00:25:64:37:fc:fb [ether] on eth0
? ( at 00:00:bc:63:d4:16 [ether] on eth0
? ( at 00:00:bc:1c:7d:31 [ether] on eth0
? ( at 00:21:9b:c0:8c:22 [ether] on eth0
? ( at 00:00:bc:c4:91:29 [ether] on eth0
? ( at 00:21:9b:c1:a1:e5 [ether] on eth0
? ( at 00:50:56:12:e5:20 [ether] on eth0
? ( at 00:50:56:01:ca:38 [ether] on eth0
? ( at 00:00:bc:1d:30:5a [ether] on eth0
? ( at 00:00:bc:c5:42:3c [ether] on eth0
If your gateway is correctly set ( and if your devices have their own default gateway set correctly everything seems fine.

Before we resort to sniffing traffic, I don't believe the problem is in linux but you never can tell...

So, please disable iptables on ubuntu machine with this
sudo iptables -F
sudo iptables -P INPUT ACCEPT
sudo iptables -P FORWARD ACCEPT
sudo iptables -P OUTPUT ACCEPT

post a tracepath output (or traceroute)
if you don't have it installed you can pull it down from repos with
sudo apt-get install tracepath traceroute

Also, because it's camera, I'have seen sometimes that these kind of devices do not use default gw configuration but rely on proxy-arp instead. This service is far from reliable so double check it.
If there is a chance, check that there is default gateway configured on remote devices.

If all this is good we will resort to tcpdump and sniffing to see where the packet has gone.

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RogerMoquinAuthor Commented:
here's what tracepath does on another cam that works
root@monitorsvr:/home/localadmin# tracepath
 1:                                    0.238ms pmtu 1500
 1:                                          2.804ms reached

but here what it does on the on I have a problem with
root@monitorsvr:/home/localadmin# tracepath
 1:                                    0.275ms pmtu 1500
 1:  no reply
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RogerMoquinAuthor Commented:
You were right about the default gateway wrongly setted on the device.
it fixes the problem.

big thanks
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