IPs , Netmasks and Broadcast.
Grant Peel
gpeel at thenetnow.com
Thu Sep 15 06:49:28 PDT 2005
Jerry,
I see, you changed the real netmask in the second and third group to 255.
Hmm, I went through this before, and unless I added 1 ip from each block
with the real netmask, the ip wouldnt take.
FYI when my ISP sends me a new block, they always give me the network,
router, broadcas address etc and I run them through ip calc, and they are
always correct.
Either way, I better revisit the Handbook/Manpage as it seems that I am
asking the same question(s) that I thought were answered 5 years ago...
Thanks for the help Jerry,
-Grant
----- Original Message -----
From: "Jerry McAllister" <jerrymc at clunix.cl.msu.edu>
To: <gpeel at thenetnow.com>
Cc: <freebsd-questions at freebsd.org>; "John Oxley" <john at yoafrica.com>
Sent: Thursday, September 15, 2005 9:31 AM
Subject: Re: IPs , Netmasks and Broadcast.
>>
>> Jerry,
>>
>> I apologise. Its late in the day for me and the email addresses are
>> blending
>> into one :-)
>>
>> Anyways, so the examples I put together are correct. Good. So I wonder
>> why,
>> the 1 IP I have, won't work with the real netmask, but only with the 255.
>> One more item of note, I see in dmesg that when it tries to apply it, the
>> message:
>
> Look carefully. I changed one thing in each group.
>
> Also, if you have a block of 128, your main mask would
> probably not be 255.255.2555.0. I think it would be 255.255.255.128.
>
> Anyway, all the aliases for any one NIC card must be 255.255.255.255.
>
>>
>> arplookup xxx.xxx.xxx.xxx failed: host is not on local network
>
> Probably because the ifconfig didn't work right with the wrong
> netmasks.
>
>
>> -Grant
>>
>> P.S. This is a small block, only 30 ips. The other 29, including 1 with
>> the
>> real netmask, is on another machine working fine, right beside the
>> machine I
>> am referencing.
>
> You will have to calculate the mask somewhat based on the switch/router
> segment you are on. It is too early for me to think it out.
>
> ////jerry
>
>>
>>
>> ----- Original Message -----
>> From: "Jerry McAllister" <jerrymc at clunix.cl.msu.edu>
>> To: <gpeel at thenetnow.com>
>> Cc: "John Oxley" <john at yoafrica.com>; <freebsd-questions at freebsd.org>
>> Sent: Thursday, September 15, 2005 8:56 AM
>> Subject: Re: IPs , Netmasks and Broadcast.
>>
>>
>> >>
>> >> Thanks John,
>> >>
>> >> What you are saying make perfect sense based on what I've had to do in
>> >> the
>> >> past. Just to clarify ...
>> >>
>> >> Lets say I have 5 machines (which I do)
>> >>
>> >> And lets say I have 10 blocks of IP address from my upline (which I
>> >> do)
>> >>
>> >> 1.1.1.1/24
>> >> 2.2.2.2/24
>> >> 3.3.3.3/24
>> >> 4.4.4.4/24
>> >> ...
>> >>
>> >> And, lets say that I need to set up various IPs, from each of the
>> >> groups
>> >> above, on all 5 of the servers.
>> >>
>> >> To keep the explanation easy to follow, I will put what I might have
>> >> in
>> >> rc.conf for each machine, Leaving out the gateway IPs as they are not
>> >> realevent to the question...my router setting work fine.
>> >
>> > No, this is not what I said. I don't know if anyone else has posted
>> > on this since then. But,
>> >
>> > The next two chunks below represent what I said.
>> >
>> > ////jerry
>> >
>> > Sever 1:
>> >
>> > hostname="machine1.mydomain.com"
>> > defaultrouter="some ip here"
>> > ifconfig_em0="inet 1.1.1.2 netmask 255.255.255.0"
>> > ifconfig_em0_alias0="inet 1.1.1.3 netmask 255.255.255.255"
>> > ifconfig_em0_alias1="inet 1.1.1.4 netmask 255.255.255.255"
>> > ...
>> > ifconfig_em0_alias2="inet 2.2.2.3 netmask 255.255.255.255"
>> > ifconfig_em0_alias3="inet 2.2.2.4 netmask 255.255.255.255"
>> > ifconfig_em0_alias4="inet 2.2.2.5 netmask 255.255.255.255"
>> > ...
>> > ifconfig_em0_alias5="inet 3.3.3.4 netmask 255.255.255.255"
>> > ifconfig_em0_alias6="inet 3.3.3.5 netmask 255.255.255.255"
>> > ifconfig_em0_alias7="inet 3.3.3.6 netmask 255.255.255.255"
>> > ...
>> >
>> > Sever 2:
>> >
>> > hostname="machine2.mydomain.com"
>> > defaultrouter="some ip here"
>> > ifconfig_em0="inet 1.1.1.5 netmask 255.255.255.0"
>> > ifconfig_em0_alias0="inet 1.1.1.6 netmask 255.255.255.255"
>> > ifconfig_em0_alias1="inet 1.1.1.7 netmask 255.255.255.255"
>> > ...
>> > ifconfig_em0_alias2="inet 2.2.2.6 netmask 255.255.255.255"
>> > ifconfig_em0_alias3="inet 2.2.2.7 netmask 255.255.255.255"
>> > ifconfig_em0_alias4="inet 2.2.2.8 netmask 255.255.255.255"
>> > ...
>> > ifconfig_em0_alias5="inet 3.3.3.7 netmask 255.255.255.255"
>> > ifconfig_em0_alias6="inet 3.3.3.8 netmask 255.255.255.255"
>> > ifconfig_em0_alias7="inet 3.3.3.9 netmask 255.255.255.255"
>> > ...
>> >
>> >
>> > -----------------------------------------------------------------
>> >
>> > Sever 1:
>> >>
>> >> hostname="machine1.mydomain.com"
>> >> defaultrouter="some ip here"
>> >> ifconfig_em0="inet 1.1.1.2 netmask 255.255.255.0"
>> >> ifconfig_em0_alias0="inet 1.1.1.3 netmask 255.255.255.255"
>> >> ifconfig_em0_alias1="inet 1.1.1.4 netmask 255.255.255.255"
>> >> ...
>> >> ifconfig_em0_alias2="inet 2.2.2.3 netmask 255.255.255.0"
>> >> ifconfig_em0_alias3="inet 2.2.2.4 netmask 255.255.255.255"
>> >> ifconfig_em0_alias4="inet 2.2.2.5 netmask 255.255.255.255"
>> >> ...
>> >> ifconfig_em0_alias5="inet 3.3.3.4 netmask 255.255.255.0"
>> >> ifconfig_em0_alias6="inet 3.3.3.5 netmask 255.255.255.255"
>> >> ifconfig_em0_alias7="inet 3.3.3.6 netmask 255.255.255.255"
>> >> ...
>> >>
>> >>
>> >> Sever 2:
>> >>
>> >> hostname="machine2.mydomain.com"
>> >> defaultrouter="some ip here"
>> >> ifconfig_em0="inet 1.1.1.5 netmask 255.255.255.0"
>> >> ifconfig_em0_alias0="inet 1.1.1.6 netmask 255.255.255.255"
>> >> ifconfig_em0_alias1="inet 1.1.1.7 netmask 255.255.255.255"
>> >> ...
>> >> ifconfig_em0_alias2="inet 2.2.2.6 netmask 255.255.255.0"
>> >> ifconfig_em0_alias3="inet 2.2.2.7 netmask 255.255.255.255"
>> >> ifconfig_em0_alias4="inet 2.2.2.8 netmask 255.255.255.255"
>> >> ...
>> >> ifconfig_em0_alias5="inet 3.3.3.7 netmask 255.255.255.0"
>> >> ifconfig_em0_alias6="inet 3.3.3.8 netmask 255.255.255.255"
>> >> ifconfig_em0_alias7="inet 3.3.3.9 netmask 255.255.255.255"
>> >> ...
>> >>
>> >> Sever 2:
>> >>
>> >> hostname="machine3.mydomain.com"
>> >> defaultrouter="some ip here"
>> >> ifconfig_em0="inet 1.1.1.8 netmask 255.255.255.0"
>> >> ifconfig_em0_alias0="inet 1.1.1.9 netmask 255.255.255.255"
>> >> ifconfig_em0_alias1="inet 1.1.1.10 netmask 255.255.255.255"
>> >> ...
>> >> ifconfig_em0_alias2="inet 2.2.2.9 netmask 255.255.255.0"
>> >> ifconfig_em0_alias3="inet 2.2.2.10 netmask 255.255.255.255"
>> >> ifconfig_em0_alias4="inet 2.2.2.11 netmask 255.255.255.255"
>> >> ...
>> >> ifconfig_em0_alias5="inet 3.3.3.10 netmask 255.255.255.0"
>> >> ifconfig_em0_alias6="inet 3.3.3.11 netmask 255.255.255.255"
>> >> ifconfig_em0_alias7="inet 3.3.3.12 netmask 255.255.255.255"
>> >> ...
>> >>
>> >> Server 3, 4 and 5 similar with repeating patterns.
>> >>
>> >> So the original question was: When setting up an IP from any given
>> >> block,
>> >> do, or should I, need to use the real netmask that my ISP has assinged
>> >> me
>> >> (for the first), then, the single host (255) netmask for each of the
>> >> rest
>> >> (Again, from a specific IP block?
>> >>
>> >> I hope it is because I have hundreds of IPs set up that way.
>> >>
>> >> The reason I ask this question (again) is because I have one IP that
>> >> does
>> >> not want to work using the above paradigm. That is to say, that it IS
>> >> the
>> >> only IP from a specific block, on a particular machine, and it won't
>> >> take
>> >> using the real netmask, it will only work using the 255 netmask.
>> >>
>> >> Sincerly,
>> >>
>> >> -Confused
>> >> (Grant).
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >> ----- Original Message -----
>> >> From: "John Oxley" <john at yoafrica.com>
>> >> To: "Grant Peel" <gpeel at thenetnow.com>
>> >> Cc: <freebsd-questions at freebsd.org>
>> >> Sent: Thursday, September 15, 2005 7:55 AM
>> >> Subject: Re: IPs , Netmasks and Broadcast.
>> >>
>> >>
>> >> > On Wed, Sep 14, 2005 at 12:00:12PM -0400, Grant Peel wrote:
>> >> >> Now I am really confused.
>> >> > First of all install ipcalc NOW.
>> >> >
>> >> >> Up until this morning I thought I had a good handle on when I need
>> >> >> to
>> >> >> use
>> >> >> the real Netmask and Broadcast.
>> >> >>
>> >> >> For example, If I have 3 servers, and my upline asigns me a block
>> >> >> of
>> >> >> 128
>> >> >> addresses, for the first ip used (from this block) on each server,
>> >> >> I
>> >> >> would
>> >> >> need to specify the IP, true netmask and a broadcase. Then, when
>> >> >> using
>> >> >> more
>> >> >> IPs from that block, I would use a 255.255.255.255 netmask and a
>> >> >> broadcast
>> >> >> equal to the IP.
>> >> >
>> >> > No, a 255.255.255.255 netmask specifies a single host. If your ISP
>> >> > has
>> >> > given you 128 IPs, that is a /25 or netmask 255.255.255.128 as shown
>> >> > :
>> >> > sysjo at hades:~$ ipcalc 192.168.254.0/25
>> >> > Address: 192.168.254.0 11000000.10101000.11111110.0 0000000
>> >> > Netmask: 255.255.255.128 = 25 11111111.11111111.11111111.1 0000000
>> >> > Wildcard: 0.0.0.127 00000000.00000000.00000000.0 1111111
>> >> > =>
>> >> > Network: 192.168.254.0/25 11000000.10101000.11111110.0 0000000
>> >> > HostMin: 192.168.254.1 11000000.10101000.11111110.0 0000001
>> >> > HostMax: 192.168.254.126 11000000.10101000.11111110.0 1111110
>> >> > Broadcast: 192.168.254.127 11000000.10101000.11111110.0 1111111
>> >> > Hosts/Net: 126 Class C, Private Internet
>> >> >
>> >> > So all your machines would have the same network and broadcast, and
>> >> > you
>> >> > would make them all use your gateway box as the default route.
>> >> >
>> >> > As you can see, a 255.255.255.255 netmask (/32) is only one host:
>> >> > sysjo at hades:~$ ipcalc 192.168.254.34/32
>> >> > Address: 192.168.254.34 11000000.10101000.11111110.00100010
>> >> > Netmask: 255.255.255.255 = 32 11111111.11111111.11111111.11111111
>> >> > Wildcard: 0.0.0.0 00000000.00000000.00000000.00000000
>> >> > =>
>> >> > Hostroute: 192.168.254.34 11000000.10101000.11111110.00100010
>> >> > Hosts/Net: 1 Class C, Private Internet
>> >> >
>> >> >
>> >> > What you need to do is use IP calc to see what the network and
>> >> > broadcast
>> >> > are and set those, although on FreeBSD 4.X (I think anyway, someone
>> >> > correct me if I am wrong) you can just put in your /etc/rc.conf
>> >> > ifconfig_bge0="inet 192.168.254.32/25"
>> >> > or
>> >> > ifconfig_bge0="inet 192.168.254.32 netmask 255.255.255.128"
>> >> >
>> >> > And FreeBSD will work out the network and broadcast for you.
>> >> >
>> >> >> Today, I was in this exact position where I was tring to add an
>> >> >> (the
>> >> >> first
>> >> >> one one THAT machine, from that block) IP from a block that is
>> >> >> almost
>> >> >> completely used up on another server, and the one I was adding it
>> >> >> to
>> >> >> would
>> >> >> not take it. When I tried adding it with a 255.255.255.255 netmask,
>> >> >> and a
>> >> >> broadcast eaqual to the amount of IPs from that block - it worked.
>> >> >
>> >> > Like I said before, there is only 1 IP in a /32 block, and the
>> >> > broadcast
>> >> > will be either a.b.c.127 or a.b.c.255 depending whether you have the
>> >> > first or second subnet inside that class C.
>> >> >
>> >> > Hope this helps
>> >> >
>> >> > -John
>> >> >
>> >> >
>> >>
>> >>
>> >> _______________________________________________
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>> >>
>> >
>> >
>> >
>>
>>
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