Re: [gentoo-user] What happened to my 2nd eth0?

[Tom H]

On Sat, Feb 21, 2015 at 11:52 PM, Walter Dnes <waltdnes@××××××××.org> wrote:


> My DSL router modem is at 192.168.123.254. I have an HDHomerun
> network TV tuner that insists on coming up somewhere in the 169.254.X.Y
> block. Up until upgrading from 32 to 64 bits, I was able to see a 2nd
> eth0 (i.e. eth0:1) using the following /etc/conf.d/net setup...
>
> config_eth0="
> 192.168.123.251/29 broadcast 192.168.123.255
> 169.254.1.1/16 broadcast 169.254.255.255"
> routes_eth0="
> default via 192.168.123.254 metric 20
> 192.168.123.248/29 via 192.168.123.254 metric 0
> 169.254.0.0/16 via 169.254.1.1 metric 0"
>
> The 2nd interface is no longer being set up. As amatter of fact, it
> appears to be totally unavailable. E.g....
>
> [d531][root][~] /etc/init.d/net.eth0 stop
>  * Unmounting network filesystems ...                                     [ ok ]
>  * Bringing down interface eth0
> [d531][root][~] ifconfig eth0:0 192.168.123.251/29 broadcast 192.168.123.255
> SIOCSIFNETMASK: Cannot assign requested address

You cannot bring up an ip alias if the "base" ip address isn't set.


> [d531][root][~] ifconfig eth0 192.168.123.251/29 broadcast 192.168.123.255
> [d531][root][~]
>
> So my system doesn't support even the concept of an alias for eth0.
> Looking at the ifconfig manpage...
>
> interface
>        The  name  of the interface.  This is usually a driver name fol-
>        lowed by a unit number, for example eth0 for the first  Ethernet
>        interface.  If  your  kernel  supports alias interfaces, you can
>        specify them with eth0:0 for the first alias of  eth0.  You  can
>        use  them  to assign a second address. To delete an alias inter-
>        face use ifconfig eth0:0 down.  Note: for every scope (i.e. same
>        net  with  address/netmask combination) all aliases are deleted,
>        if you delete the first (primary).
>
> I see "If  your  kernel  supports alias interfaces". During the
> upgrade, I built the kernel from square 1. I already ran into problems
> with not enabling FUSE in the new kernel, which killed MTP until I
> enabled it. I wouldn't be surprised if I've disabled some kernel
> parameter which is required to enable interface aliases. I didn't see
> anything obvious in "make menuconfig". A Google search turned up a
> gazillion examples of "how to create an alias using ifconfig". That's
> not what I want. I want the kernel setting that allows creating alias
> interfaces.

CONFIG_IP_ALIAS was dropped with v2.4

From 2.2 alias.txt:

For IP aliasing you must have IP_ALIAS support included by static
linking.

From 2.4 alias.txt:

IP-aliases are additional IP-adresses/masks hooked up to a base
interface by adding a colon and a string when running ifconfig.
This string is usually numeric, but this is not a must.

IP-Aliases are avail if CONFIG_INET (`standard' IPv4 networking)
is configured in the kernel.

From 3.19 alias.txt:

IP-aliases are an obsolete way to manage multiple IP-addresses/masks
per interface. Newer tools such as iproute2 support multiple
address/prefixes per interface, but aliases are still supported
for backwards compatibility.