2 logical interfaces in same subnet, problems...

Derek Ragona derek at computinginnovations.com
Tue Sep 16 00:18:29 UTC 2008

At 11:38 AM 9/15/2008, Andy Smith wrote:
>   I would like to configure a second sub/cloned interface on a FreeBSD 
> 5.3 system. I have read various bits
>and pieces on the subject but I cannot ping (from another server) the 
>second IP which I have configured.
>The steps I took to achieve this are:
>kldload if_vlan
>ifconfig fxp0.1 create
># then add the IP to fxp0.1
># after which my interfaces look something like:
>         options=8<VLAN_MTU>
>         inet netmask 0xffffff00 broadcast
>         inet6 fe80::203:47ff:fe71:21e7%fxp0 prefixlen 64 scopeid 0x1
>         ether 00:03:47:71:21:e7
>         media: Ethernet autoselect (100baseTX <full-duplex>)
>         status: active
>fxp0.1: flags=8842<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>         inet6 fe80::203:47ff:fe71:21e7%fxp0.1 prefixlen 64 scopeid 0x8
>         inet netmask 0xffffffff broadcast
>         ether 00:03:47:71:21:e7
>         media: Ethernet autoselect (100baseTX <full-duplex>)
>         status: active
>         vlan: 1 parent interface: fxp0
> >From this server itself I can ping the second IP, but from 
> other systems I can only ping
>Im most familiar with Solaris and this type of config works no probs with 
>Solaris, is there something else I
>have to configure on FreeBSD? For example I found it wouldnt let me use 
>the normal subnet and I then read
>that for a second IP on the same subnet it should be set to -1
>Any ideas? thanks for any help,


You are doing this the wrong way for FreeBSD.  The method you used I've 
seen in Redhat.

Just add a line like this to /etc/rc.conf:
ifconfig_fxp0_alias1=" netmask 0xffffffff"

You can also do it at the command line:
ifconfig fxp0 alias netmask 0xffffffff

You don't need anything else.  No kernel mods.  You will just have another 
IP stack running on your NIC.


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