Incorrect netmask in network configuration

**AMSM** · 10-14-2013, 06:06 PM

Why would you even need a netmask.

**Spudstr** · 10-16-2013, 05:17 AM

Originally posted by EN1GMA

Hi guys,

I had some problems with netmask of my additional IPs that was showing 255.255.255.0 instead of 255.255.255.255.
I fixed that and contacted my hosting provider support to confirm if everything was correct with the new IP configuration showing the log of the command "ifconfig":

And they said this:

I tried to fix by running the command:

Code:

sed -i 's/94.23.78.255/94.23.78.68/g' /etc/ips; /etc/init.d/ipaliases restart

But I think that something is wrong.
Here goes the log:

I notice two things:

1- I don't have 'eth0:0' anymore,now I have a 'eth0:cp1' and 'eth0:cp2', it seems that was renamed. Is this ok?

2- It seems that eth0:cp1 is fine now:
inet addr:94.23.78.68 Bcast:94.23.78.68 Mask:255.255.255.255

But eth0:cp2 (old eth0:0 that was already fine) is not:
inet addr:178.32.52.69 Bcast:178.32.52.255 Mask:255.255.255.255

Any ideas? Can someone help me with these?

Thank you guys!

Regards!!

According to documentation..
These are subinterfaces and a method of adding additional IP addresses along with their subnets to an interface. The part after the colon is arbitrary.

iptables cannot reference subinterfaces, so any rules required would be based on IP addresses, but bound to the physical interface if required.

As far as netmasks go. having a /32 netmask on an alias ip is fine actually. since the only one that matters is the netmask that defines the default route which is accessible is the main IP on the box, well you could use any actually as long as your default gateway is pointing to an aces sable IP on that netmask. Since they are different ips not in the same broadcast domain issuing a /32 on each IP is the correct way to do this masking.

Now with that being said this is actually HORRIFIC practice and VERY poor network design which will lead into a lot of "shit talking" on the broadcast domain, lots of crap traffic and actually you are vulnerable to a broadcast flood on the broadcast domain, which would take you down and everyone else on that broadcast domain if it was to happen.

In short this his horrible, while I realize this is OVH.. its not a real good design to do.

**EN1GMA** · 10-16-2013, 06:56 AM

Spudstr, thank you for your reply buddy.

So what do you suggest to do?

Thanks once again!

**Spudstr** · 10-16-2013, 08:52 AM

Originally posted by EN1GMA

Spudstr, thank you for your reply buddy.

So what do you suggest to do?

Thanks once again!

Stick with the /32's and don't change the netmasks on them.

Unless they just don't work? then that is a different set of issues.

Incorrect netmask in network configuration

Incorrect netmask in network configuration

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