Fargusson.Alan wrote:
The problem I eluded to is that some network cards and hubs don't send and
receive at the same time, so if you send a packet to your own IP address you
don't see it come back. That means that you won't be able to access machine x
from machine x using the IP address. The loopback interface always works,
which is why most systems either use a special route, or has a /etc/host entry
to a 127.* address.
As I said before, I don't want my external IP address/hostname
apparently working when the interface is down.
I am going to guess that virtual networks on z/VM will always act as if the
send and receive at the same time, so this isn't going to be a problem under
z/VM. The real network cards for zSeries may even handle this case specially.
-----Original Message-----
From: Linux on 390 Port [mailto:[EMAIL PROTECTED] Behalf Of
John Summerfield
Sent: Friday, September 12, 2008 9:35 AM
To: [email protected]
Subject: Re: 127.0.0.2 in /etc/hosts?
Fargusson.Alan wrote:
This is a question for Novell, although I think they are changing to conform to
some new network standard. It isn't just Novell that is changing this. I have
seen some other Unix and Linux systems doing this as well (although I can't
remember which one right now).
I just did a netstat -r on SLES 10 SP1 and I didn't see my IP routed to the
loopback interface. I did a netstat -r on Windows and I did. It may be that
SP1 fails to access itself on some networks. This may be the reason for the
change.
I think the issue is that this case has been handled in the routing tables. If
you do a route command (or a netstat -r) on most systems you will see that the
IP address of your system is specially routed to the loopback interface. The
problem is that routing tables can get messed up, and things break. Having he
hostname specifically 127.* avoids some of these problems.
I'd never seen that before. However, here's a Leopard:
gargant:~ root# netstat -rn
Routing tables
Internet:
Destination Gateway Flags Refs Use Netif Expire
default 192.168.1.252 UGSc 5 2 en1
127 127.0.0.1 UCS 0 0 lo0
127.0.0.1 127.0.0.1 UH 6 44459 lo0
169.254 link#5 UCS 1 0 en1
169.254.112.1 0:30:65:2:4:a9 UHLW 0 0 en1 398
192.168.1 link#5 UCS 4 0 en1
192.168.1.71 0:30:65:2:4:a9 UHLW 0 0 en1 422
192.168.1.250 127.0.0.1 UHS 0 0 lo0
192.168.1.252 0:d:56:c5:48:30 UHLW 3 67 en1 1168
Internet6:
Destination Gateway
Flags Netif Expire
::1 link#1
UHL lo0
fe80::%lo0/64 fe80::1%lo0
Uc lo0
fe80::1%lo0 link#1
UHL lo0
fe80::%en1/64 link#5
UC en1
fe80::203:93ff:fec0:4b18%en1 0:3:93:c0:4b:18
UHL lo0
ff01::/32 ::1
U lo0
ff02::/32 fe80::1%lo0
UC lo0
ff02::/32 link#5
UC en1
gargant:~ root#
So latest OS X is doing it.
My Debian/Etch system does not. Whether it's because Debian does not, or
because it has several active interfaces I don't know.
My sl5/CentOS5 systems do not.
My WBEL4/CentOS4 systems do not.
I imagine that route would allow one to use the IP address of a down
interface. I'm not sure I'd want that.
I suspect that having that entry in /etc/hosts would do the same thing,
again I'm not sure I'd want that.
If a network interface is down, I want it down and obviously not
working. Doing otherwise might hide a problem and prevent its being
discovered in a timely manner, and complicate diagnosis of problems when
it cannot be accessed from outside, but works from the host itself.
I also wonder what it might do to my firewall rules.
A problem I do have is connected with my one public IP address. If mo
(soho-grade) ADSL router has it, and I try to access the external IP
address from inside the LAN, the ADSL router gets confused when traffic
arrives _from_ the LAN that is supposed to be going _to_ the LAN. I have
worked around that one by creating a dummy interface (ifconfig dummy0)
on the server. Putting the ADSL router in bridge mode and running pppoe
on the Linux box works too.
However, I don't think this solution is directed to my problem.
-----Original Message-----
From: Linux on 390 Port [mailto:[EMAIL PROTECTED] Behalf Of
John Summerfield
Sent: Thursday, September 11, 2008 6:03 PM
To: [email protected]
Subject: Re: 127.0.0.2 in /etc/hosts?
Michael MacIsaac wrote:
I can see how SuSE/Novell can argue that it is a valid value (i.e.
"working as designed"), but if it affects important applications such as
SAP and DB2, I can see how it might be viewed as a bug by the customer.
"working as designed" does not preclude a faulty design.
There might be some debate as to where the faulty design(s) exist, but
_I_ would argue against a design change that breaks stuff.
What problem is Novell trying to fix with this?
--
Cheers
John
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