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I am handling 34 Debian servers. Two of these are diskful machines (which boot from their HDs), the remaining 32 are PXE clients without disks.

The two machines with disks are called uni01 and uni02. uni01 sends a single system image via NFS to the nodes that do network booting (it also runs DHCP + TFTP).

The network is a class A subnet (mask Problem is, one specific node (uni19) cannot contact uni02. They're in the same subnet, the other hosts can connect just fine, except this one.

root@uni19:~# traceroute uni02
traceroute to uni02 (, 30 hops max, 60 byte packets
1  uni19 (  2997.791 ms !H  2997.789 ms !H  2997.784 ms !H

However arping works for uni02:

root@uni02:/home/einar# arping uni19
60 bytes from 10:1f:74:2c:78:aa ( index=0 time=172.946 usec
60 bytes from 10:1f:74:2c:78:aa ( index=1 time=208.391 usec

It doesn't for uni19:

root@uni19:~# arping uni02
--- statistics ---
4 packets transmitted, 0 packets received, 100% unanswered (0 extra)

Routing tables:

root@uni19:~# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         uni01          UG    0      0        0 eth0    *        U     0      0        0 eth0

 root@uni02:~# route
 Kernel IP routing table
 Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
 default         uni01          UG    0      0        0 eth0.682    *        U     0      0        0 eth0.682   UG    0      0        0 eth0.682   UG    0      0        0 eth0.682

uni01 and uni02 use specific interfaces for a VLAN, but all the other hosts have been switched to the same VLAN to be able to communicate (in fact, also uni01 is on the same VLAN, but all serers are able to PXE boot).

What can I do to troubleshoot this? I already confirmed there are no firewalls up.

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have you already tried tcpdump? – dawud Jul 11 '13 at 12:28
That's what I'm doing right now. Will edit the post (or add an answer) once I'm done. – Einar Jul 11 '13 at 12:33
up vote 0 down vote accepted

PEBKAC. That's the only way I could describe this.

The reason why this happened: a typo in /etc/network/interfaces assigned the wrong broadcast address to the interface in uni02, address that by chance was the one used by uni19. So I replaced the broadcast address and all is fine.

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