IPs , Netmasks and Broadcast.
Grant Peel
gpeel at thenetnow.com
Thu Sep 15 06:11:18 PDT 2005
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:
arplookup xxx.xxx.xxx.xxx failed: host is not on local network
-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.
----- 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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