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Old 12-19-2008, 12:26 PM   #1
sharkhuang
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Mutil IP issue


What is the different between multi IP on one real interface and multi IP on one true interface and alias interface. For example:

Both 10.0.0.1 and 10.0.0.2 IP attach on eth0
IP addr add 10.0.0.1/24 dev eth0
IP addr add 10.0.0.2/24 dev eth0

VS

10.0.0.1 on eth0
10.0.0.2 on eth0:1

ifconfig eth0 up 10.0.0.1
ifconfig eth0:1 up 10.0.0.2

Last edited by sharkhuang; 12-19-2008 at 12:48 PM.
 
Old 12-19-2008, 12:32 PM   #2
eco
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Hi,

You simply can't have multiple IPs on one interface without using aliases (ethx:x).

So to use 10.0.0.1 and 10.0.0.2 use eth0, you need to have:

eth0 - 10.0.0.1
eth0:0 - 10.0.0.2

Hope this helps
 
Old 12-19-2008, 12:36 PM   #3
sharkhuang
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Quote:
Originally Posted by eco View Post
Hi,

You simply can't have multiple IPs on one interface without using aliases (ethx:x).

So to use 10.0.0.1 and 10.0.0.2 use eth0, you need to have:

eth0 - 10.0.0.1
eth0:0 - 10.0.0.2

Hope this helps
No! I can if I use the IP addr add xxxx command.
 
Old 12-19-2008, 12:53 PM   #4
eco
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?
Please explain with an example.
Thanks
 
Old 12-20-2008, 05:52 AM   #5
sharkhuang
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Quote:
Originally Posted by eco View Post
?
Please explain with an example.
Thanks
Both 10.0.0.1 and 10.0.0.2 IP attach on eth0
IP addr add 10.0.0.1/24 dev eth0
IP addr add 10.0.0.2/24 dev eth0

VS

10.0.0.1 on eth0
10.0.0.2 on eth0:1

ifconfig eth0 up 10.0.0.1
ifconfig eth0:1 up 10.0.0.2
 
Old 12-20-2008, 06:32 AM   #6
eco
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I men, what command would you use to set two IPs on the same interface without using an alias?

I'd guess the second command would nullify the first.

Still, if that where possible, the alias permits you to route through a device rather than an IP I supose.
 
Old 12-20-2008, 06:56 AM   #7
sharkhuang
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Quote:
Originally Posted by eco View Post
I men, what command would you use to set two IPs on the same interface without using an alias?

>> ip addr add

I'd guess the second command would nullify the first.

Still, if that where possible, the alias permits you to route through a device rather than an IP I supose.

I got some answer:

> Just wondering what the differences between using "ip addr add ..."
> and defining an interface alias with "ifconfig eth0:0 ..." are.
Aliases have been in use in times before Christ - they define different
interfaces (so different routing rules, tc, firewall...).
ip addr is reasonable approach to 'one if, several addresses' problem.
Use the latter only or mess with inconvenient problems that arise.

> Any (dis)advantages in either method?
> Any experiences?
As I wrote above.
 
Old 12-20-2008, 07:02 AM   #8
sharkhuang
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Other answer

Damian 'legion' Szuberski a écrit :
> On 2007-04-10, kianusch@gmail.com wrote:
>
>>Just wondering what the differences between using "ip addr add ..."
>>and defining an interface alias with "ifconfig eth0:0 ..." are.
>
> Aliases have been in use in times before Christ - they define different
> interfaces (so different routing rules, tc, firewall...).

No they don't - at list on Linux. The eth0:0 thing is not an interface
but only a kind of label associated to the address. The label does not
exist for kernel networking functions such as routing, packet filtering
and so on. Only the real interface and its addresses (including the
aliases) exist.

Once created, I have not seen any operational difference between aliases
created by ifconfig and addresses added by "ip addr". Both add addresses
and direct routes to network interfaces. However addresses created by
"ip addr" without an explicit label (default label is the interface
name) do no show in ifconfig (but it works the same). Also, alias
handling in ifconfig is somehow inconsistant : you set the label DOWN
(like an interface, which it is not) to delete it.

Note that you can also add an IP address to an interface (and create an
alias) with "ifconfig ethX add...".
 
  


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