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@xxxxxxxxxx >> 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).
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