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Old 08-02-2009, 02:41 PM   #1
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Question RHEL4.5: Can't ping VLAN IP on same network/subnet

The interface IP is the same subnet as the VLAN IP of the switch directly connected to it but RHEL server cannot ping it. The server can however ping the other servers connected to the same VLAN of the same subnet. Why is that?
I tried connecting a.. ehhrmm... windows machine to the switch, used an IP of the same subnet and I can ping the VLAN IP ok.

Interface details:
eth0 Link encap:Ethernet HWaddr 00:21:5E:74:83:B9
inet addr: Bcast: Mask:
inet6 addr: fe80::221:5eff:fe74:83b8/64 Scope:Link
RX packets:101 errors:0 dropped:0 overruns:0 frame:0
TX packets:689 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:32212 (31.4 KiB) TX bytes:90480 (88.3 KiB)
Interrupt:169 Memory:ce000000-ce012100

'route -n' output:
Destination Gateway Genmask Flags Metric Ref Use Iface U 0 0 0 eth1 U 0 0 0 eth0 UG 0 0 0 eth0 UG 0 0 0 eth0 UG 0 0 0 eth2 U 0 0 0 eth2 U 0 0 0 eth2

'arp -a' output:
? ( at 00:07:85:17:82:15 [ether] on eth2
? ( at 00:21:59:CF:1B:80 [ether] on eth2
? ( at 00:15:17:B0:72:28 [ether] on eth2
? ( at 00:21:5E:70:1B:2E [ether] on eth2

eth2,, is connected to the same switch but on a different VLAN. Why is the connection of eth0 to switch not shown in arp -a?

I'm using a Juniper Ex4200, and the VLAN IP is I cannot ping this IP but when I add it to the ARP table via "arp -s <mac address of switch>", I can ping it.

And I can ping other servers connected to the same VLAN, e.g.,

I do not have to add the VLAN IP to the interface's ARP table all the time to be able to ping it don't I?? They're on the same subnet and directly connected!

Thanks in advance.

Last edited by yujinn; 08-02-2009 at 02:42 PM.
Old 08-03-2009, 07:30 AM   #2
Registered: Nov 2007
Location: /home/watcher69b
Distribution: RH, Fedora & CentOS
Posts: 548

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is the iptables enabled on your RH box? Try iptables -F and then ping again.

If that still does not work then can you sniff the traffic using wireshark to see what is happening?

My thinking is that if you replaced the box with another and it worked i would say that the RH system is sending icmp traffic but that same traffic is being dropped when the response is returned to the RH system


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