Steffen Maier wrote:
On actually sending something to that address, the following entries are
added to the routing cache, revealing that the ICMP echo request was
sent on the loopback interface and the echo reply was received from the
loopback:
[EMAIL PROTECTED] sbin]# ip route list table cache
local X.Y.108.38 dev lo src X.Y.108.38
cache <local> mtu 16436 advmss 16396 hoplimit 64
local X.Y.108.38 from X.Y.108.38 dev lo
cache <local> ipid 0x8142 mtu 16436 advmss 16396 hoplimit 64
...
I imagine that route would allow one to use the IP address of a down
interface. I'm not sure I'd want that.
Yes, you could reach your own host via the IP address of a down
interface since packets would go through loopback. At least from a
performance point of view, forwarding packets destined for oneself
efficiently within the host is a good thing.
AFAIK this has been the usual behavior of Unix IP stacks since BSD.
Not being willing to believe anyone (even myself sometimes!) I thought
to try a little experiment. I have three peecess on a KVM and two are
currently booted into Linux.
I configured eth0:0 with a 127.10 address and confirmed I can ping it.
On another box, I configured eth0:0 with a different 127.10 address in
the same network.
Each can ping itself, neither can ping the other.
This is completely consistent with Steffen's contribution:-)
Then I had an "A hah!," so tried
"ifconfig lo down"
Now I cannot ping even the 127.10 address assigned to eth0:0.
This too is completely consistent with Steffen's contribution:-)
And finally, I tried to ping my external IP address while lo is down,
and that does not work either (but pinging another box is okay).
--
Cheers
John
-- spambait
[EMAIL PROTECTED] [EMAIL PROTECTED]
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