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Subjecteth0 and loopback problems.
Hi all!
I think it's a bug....

HOSTA# ifconfig eth0 192.168.0.1
HOSTA# ifconfig eth0 down
HOSTA# ping 192.168.0.1
(the ping works, like all other ICMP / TCP /UDP ... application.
In other words: all work like eth0 in UP mode when source and
destination point comunicate via loopback device.
I think it's not correct because if eth0 is DOWN for all the hosts in
LAN should be down for me too. Or not?

Suppose another conf:

HOSTA# ifconfig
eth0 Link encap:Ethernet HWaddr 00:10:DC:C3:5E:FF
inet addr:192.168.0.1 Bcast:192.168.0.255 Mask:255.0.0.0
BROADCAST MULTICAST MTU:1500 Metric:1
eth1 Link encap:Ethernet HWaddr 00:0E:35:74:16:67
inet addr:192.168.0.2 [...]
UP BROADCAST RUNNING MULTICAST MTU:1500
lo [...]

HOSTB# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:00:24:C8:4A:7D
inet addr:192.168.0.1 Bcast:1.255.255.255 Mask:255.0.0.0
UP BROADCAST RUNNING MULTICAST MTU:1500
[...]

So, HOSTA and HOSTB share the same ip but: HOSTA eth0 is DOWN; HOSTA eth1 is
UP, HOSTB eth0 is UP. So, no conflict should be possible.
but:

HOSTB# ping 192.168.0.2
(does not reply)

So I suppose that HOSTA route the icmp reply through its lo.
But:

HOSTA# tcpdump -i lo
doesn't show any reply, and

HOSTA# tcpdump -i eth0
it's not permitted, because eth0 is DOWN.

The same result for TCP protocol (tested with hping).
Operative conditions: Linux 2.6.14, HOSTA eth1 is wifi.
Regards
JohnnyRun
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