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. Thanks Levi