link-local address via ifconfig

link-local address via ifconfig

[Anand Kumria]

Hi,

There are plenty of people who still use ifconfig to list the addresses
assigned to their network interfaces (I know, ifconfig is broken) and
who then parse the output.

However the kernel puts link-local scoped address first if the address
list of an interface, so an interface like:

eve:[~]% ip addr show wlan0
3: wlan0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:12:f0:03:d9:e7 brd ff:ff:ff:ff:ff:ff
    inet 169.254.182.108/16 brd 169.254.255.255 scope link wlan0
    inet 192.168.2.2/24 brd 192.168.2.255 scope global wlan0
    inet6 fe80::212:f0ff:fe03:d9e7/64 scope link
       valid_lft forever preferred_lft forever

appears as:
eve:[~]% ifconfig wlan0
wlan0     Link encap:Ethernet  HWaddr 00:12:F0:03:D9:E7
          inet addr:169.254.182.108  Bcast:169.254.255.255 Mask:255.255.0.0
          inet6 addr: fe80::212:f0ff:fe03:d9e7/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
	  [... elided ...]

Is there any reason to put the link-local address first in the list?

I've had a number of bugreports (or outright panic attacks) where the 
problem turned out to be that ifconfig was reporting the link-local 
address first, rather than the global/site one.

Thanks,
Anand

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Re: link-local address via ifconfig

[Herbert Xu]

Anand Kumria <wildfire@progsoc.uts.edu.au> wrote:
> 
> There are plenty of people who still use ifconfig to list the addresses
> assigned to their network interfaces (I know, ifconfig is broken) and
> who then parse the output.

If people insist on using hammers on screws, the answer is not to improve
the hammer.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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Re: link-local address via ifconfig

[Ingo Oeser]

Hi Anand,

Anand Kumria wrote:
> There are plenty of people who still use ifconfig to list the addresses
> assigned to their network interfaces (I know, ifconfig is broken) and
> who then parse the output.
> 
> However the kernel puts link-local scoped address first if the address
> list of an interface, so an interface like:

> Is there any reason to put the link-local address first in the list?
> 
> I've had a number of bugreports (or outright panic attacks) where the 
> problem turned out to be that ifconfig was reporting the link-local 
> address first, rather than the global/site one.

This can be worked around by defining an "alias interface" this way
"ip address add 169.254.182.108/16 brd 169.254.255.255 scope link dev eth0 label eth0:0"
(see: "label eth0:0" is appended)

So in reality this is no problem for users.


Regards

Ingo Oeser