IP Range

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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

16 thoughts on - IP Range

  • You can (and are encouraged) to specify the NETMASK as well in that range file. I don’t know why it uses that mask and broadcast; maybe it inherits them from other already configures interface?

  • From: Birta Levente

    Never used ifcfg-eth0-range, but did you try 49 to 54 instead of 48 to 55?

    $ ipcalc 192.168.1.48/29
    Address:

  • 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

  • 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

  • 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).

  • 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

  • From: Birta Levente

    So maybe you do not want to (or cannot) use an ifcfg range file and just use 1 eth0 file + 7 alias files…

    JD

  • It very much depends on if he bought a routed subnet or bought 8
    individual IPs. It’s very possible the OP _does_ have 8 IPs to play with but, because it’s not a subnet, he may need to configure them individually.

    (I had a friend who bought 4 IPs from BellAtlantic DSL in the late 90s that were 4 available IPs and not a routed subnet; his OpenBSD firewall machine would proxy-arp for the Windows machines sitting behind it)

  • I’ve also seen DSL networks like this where those extra IPs are bridged not routed. in these cases, you use the same gateway as the ‘main’ IP, but usually the main IP has a /24 or whatever mask that encompasses ALL
    the IPs.

    regardless, the OP should contact the ISP and find out what the mask and gateway are for the extra IPs.

  • on 8/2/2012 12:54 PM John R Pierce spake the following:
    I guess with the ipv4 drought, this will become even more common… Until everyone gets to ipv6…

  • Thank you all for your time …

    But I have another question:

    Why is a difference in setting up with icfg-eth0:0 and ifconfig ?
    As I sad, setting up all 8 IP-s with ifconfig works perfectly. Why if I specify explicitly the subnet mask in ifcfg-eth0:0 then appear other?

    Thanks

    Levi

  • I’m not surprised and I’m really beginning to develop an abject hate for all things networking in Fedora/RHEL land. I’s kludges upon kludges to accommodate new ways of doing things while keeping backwards compatibility within a framework of stitched together shell scripts.

    Regards,
    Dennis

  • [For the archives, since I think Johnny just hit the wrong number key…..]

    192.168.1.63 would be the correct broadcast address; .64 would be the network address of the next subnet.

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