[CentOS] IP range

Birta Levente blevi.linux at gmail.com
Thu Aug 2 15:07:50 UTC 2012


On 02/08/2012 17:52, Johnny Hughes wrote:
> On 08/02/2012 09:33 AM, Birta Levente wrote:
>> 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
>>>
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> CentOS mailing list
>>> CentOS at centos.org
>>> http://lists.centos.org/mailman/listinfo/centos
>>>
>> 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.
>
> What if you do this:
>
> ifcfg-eth0-range1:
> ONBOOT="yes"
> IPADDR_START="192.168.1.49"
> IPADDR_END="192.168.1.54"
> CLONENUM_START="1"
> BROADCAST=192.168.1.55
> NETMASK=255.255.255.248
> NETWORK=192.168.1.48
>
> (with a .248 subnet, you can not use the first address (192.168.1.48) or
> the last address (192.168.1.55) on a device, they are the Network
> Address and the Broadcast Address ... so an 8 IP subnet has 6 usable
> addresses.  Also, one of those 6 addresses will also need to be assigned
> to the gateway router if you need to talk to another network, so you
> really only have 5 addresses that you can assign for use).
>
>
>
>
> _______________________________________________
> CentOS mailing list
> CentOS at centos.org
> http://lists.centos.org/mailman/listinfo/centos
>

Nope....

Work only .49 and .50

I bought 8 public IP-s ... so 8 IPs have to get work.
In the hosting specification this IPs is usable with xxx.xxx.xxx.48-55 
with subnet mask 255.255.255.255 with no gateway.

As I sad, works perfectly with this command (8 times, of course :) ):
#ifconfig eth:(0 to 7) xxx.xxx.xxx.(48-55) netmask 255.255.255.255

Thanks

Levi










More information about the CentOS mailing list