Anand Buddhdev wrote:
I have a FreeBSD 4.7 system, with 3 ethernet cards. The first two
are recognised as fxp0 and fxp1 and the second as em0 (intel gigabit
card). I configured the em0 with address I then wanted
to configure fxp0 with the address, and also connect it
to the switch so that I can connect to the server via both addresses.
However, FreeBSD's ifconfig command fails, and won't let me add the second
address to the fxp0 interface. I read the manual page about ifconfig,
and read about aliases, where it said that for aliases, I must use the
netmask /32. When I do try to add the second address with a netmask of
/32, it works, but it doesn't make sense to me. How is that interface
going to to know that it is part of a /24 network if I use a /32 netmask?

Would anyone be kind enough to explain why:

1. For aliases, I need the /32 mask
I didn't know that you did.  I've certainly had aliases that weren't /32

2. Adding a second IP to a *different* network card in the same server
does not work if the second IP is within the network of the first one.
Because it breaks routing and the basic concept of IP addys and netmasks.
If you have two NICs on the same network, how is the kernel supposed to
route packets?

If you want this setup as a failover solution, there are other ways.
There's a program in the ports (I can't remember the name, you'll have to
do some research) that will monitor an interface, and if it becomes non-
responsive, run a script of your choosing.  Thus, you can have it start
up the other network card if the first fails.

If failover isn't what you're looking for, then I'd reconsider your
network topology.  It doesn't really make sense to have 2 NICs with the
same network number in one machine.

Bill Moran
Potential Technologies

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