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Date: Tue, 16 Sep 2008 09:45:29 +0700 (ICT)
Message-Id: <200809160245.m8G2jTMe088981@banyan.cs.ait.ac.th>
From: Olivier Nicole <on@cs.ait.ac.th>
To: a.smith@ukgrid.net
In-reply-to: <041601c91751$6d518a60$6600a8c0@computer> (a.smith@ukgrid.net)
References: <041601c91751$6d518a60$6600a8c0@computer>
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Cc: freebsd-questions@freebsd.org
Subject: Re: 2 logical interfaces in same subnet, problems...
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>   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.
> fxp0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>         options=8<VLAN_MTU>
>         inet 10.10.10.1 netmask 0xffffff00 broadcast 10.10.10.255
> fxp0.1: flags=8842<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>         inet6 fe80::203:47ff:fe71:21e7%fxp0.1 prefixlen 64 scopeid 0x8
>         inet 10.10.10.2 netmask 0xffffffff broadcast 10.10.10.255

I am not sure how you configured your interface, here ifconfig would
show:

em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        options=1b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING>
        inet6 fe80::20e:cff:fe5c:3228%em0 prefixlen 64 scopeid 0x1 
        inet 192.41.170.14 netmask 0xffffff00 broadcast 192.41.170.255
        inet 192.41.170.40 netmask 0xffffffff broadcast 192.41.170.40
        inet 192.41.170.41 netmask 0xffffffff broadcast 192.41.170.41

etc. I have only one interface with many IPs. I configure it in
/etc/rc.conf with:

ifconfig_em0="inet 192.41.170.14  netmask 255.255.255.0"
ifconfig_em0_alias0="inet 192.41.170.40/32"
ifconfig_em0_alias1="inet 192.41.170.41/32"

Olivier