[CentOS] IP range

[Birta Levente]

On 02/08/2012 17:24, Johnny Hughes wrote:
> On 08/02/2012 09:00 AM, Birta Levente wrote:
>> Hi all
>>
>> Can someone explain me this:
>>
>> ifcfg-eth0-range1:
>> ONBOOT="yes"
>> IPADDR_START="192.168.1.48"
>> IPADDR_END="192.168.1.55"
>> CLONENUM_START="1"
>>
>> Why Bcast is 192.168.1.51 and why Mask is 255.255.255.252 ?
>>
>> OS: Centos 6.3/64bit
>>
>>
>> Thanks
>>
>> Levi
>>
>> # ifconfig
>>
>> eth0:1    Link encap:Ethernet  HWaddr 00:9C:02:99:FA:00
>>             inet addr:192.168.1.48  Bcast:192.168.1.51  Mask:255.255.255.252
>>             UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>>             Interrupt:16 Memory:fbee0000-fbf00000
>>
>> eth0:2    Link encap:Ethernet  HWaddr 00:9C:02:99:FA:00
>>             inet addr:192.168.1.49  Bcast:192.168.1.51  Mask:255.255.255.252
>>             UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>>             Interrupt:16 Memory:fbee0000-fbf00000
>>
>> eth0:3    Link encap:Ethernet  HWaddr 00:9C:02:99:FA:00
>>             inet addr:192.168.1.50  Bcast:192.168.1.51  Mask:255.255.255.252
>>             UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>>             Interrupt:16 Memory:fbee0000-fbf00000
>>
>> eth0:4    Link encap:Ethernet  HWaddr 00:9C:02:99:FA:00
>>             inet addr:192.168.1.51  Bcast:192.168.1.51  Mask:255.255.255.252
>>             UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>>             Interrupt:16 Memory:fbee0000-fbf00000
>>
>> eth0:5    Link encap:Ethernet  HWaddr 00:9C:02:99:FA:00
>>             inet addr:192.168.1.52  Bcast:192.168.1.51  Mask:255.255.255.252
>>             UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>>             Interrupt:16 Memory:fbee0000-fbf00000
>>
>> eth0:6    Link encap:Ethernet  HWaddr 00:9C:02:99:FA:00
>>             inet addr:192.168.1.53  Bcast:192.168.1.51  Mask:255.255.255.252
>>             UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>>             Interrupt:16 Memory:fbee0000-fbf00000
>>
>> eth0:7    Link encap:Ethernet  HWaddr 00:9C:02:99:FA:00
>>             inet addr:192.168.1.54  Bcast:192.168.1.51  Mask:255.255.255.252
>>             UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>>             Interrupt:16 Memory:fbee0000-fbf00000
>>
>> eth0:8    Link encap:Ethernet  HWaddr 00:9C:02:99:FA:00
>>             inet addr:192.168.1.55  Bcast:192.168.1.51  Mask:255.255.255.252
>>             UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>>             Interrupt:16 Memory:fbee0000-fbf00000
>
> That is obviously not going to work ... a 255.255.255.252 mask is a 4 IP
> subnet, with only 2  usable addresses and a network number and a
> broadcast address.  The only free addresses in
> 192.168.1.48/255.255.255.252 are .49 and .50
>
> The Broadcast and Mask settings are likely in your ifcfg-eth0 file and
> not in the range file at all.
>
> The Mask would either be set manually in ifcfg-eth0 ... or by the DHCP
> server if you get DHCP. The Broadcast address would automatically be set
> based on the Mask, unless it is overridden in ifcfg-eth0.
>
> If the address is set via DHCP, you need to change the subnet mask on
> the DHCP server as that is where it comes from.
>
> If you want 8 usable addresses (including the Network number, a gateway
> address, and a Broadcast address), that would mean you need at least 11
> IPs in that subnet ... the closest fit would be a 255.255.255.240 subnet
> (which has 16 addresses).  If you were to want to use th 255.255.255.240
> subnet, then 192.168.1.48 would not be available as it would the the
> Network number for that subnet ... the usable addresses would be
> 192.168.1.49-63 that case and the Broadcast Address would be 192.168.1.64
>
> Since this is on a private network, why are you not just using the full
> 192.168.1.0 network with a 255.255.255.0 subnet?
>
> I guess the real question is, what are you trying to do :D
>
>
>
>
>
>
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I have eth0 with public IP, netmask is 255.255.255.252.
Additionally I own 8 public IPs xxx.xxx.xxx.48-55 with class subnet mask 
255.255.255.248

If I set up with ifconfig eth:(0 to 7) xxx.xxx.xxx.(48-55) netmask 
255.255.255.255 it's work.

But if I set up the ifcfg-eth0:(0-7) files with the same IP and netmask 
it's not work. ifconfig show me the 255.255.255.252 netmask even if in 
file other netmask is specified.
The same situation in ifcfg-eth0-range1 case.


Thanks

Levi