multiple uplinks from ISP

[mc]

Hi all,

If I have the following on hand...
- 2 FastEthernet uplinks from ISP
- 1 GigabitEthernet port on my switch
- a subset of a /24 allocated by ISP
The gigabit ethernet link should be connecting to my internal network.

Problem: My internal network has been maxing out its 100Mbps limit, but my
ISP doesn't want to give us a gigabit link, though they are willing to
provide another 100Mbps link for us.
Aim: Use 2*100Mbps uplinks in place of a gigabit link.

I was wondering if it was possible to build a FreeBSD box acting as a
router, connecting up my internal network (gigabit interface) and the
uplinks provided by my isp (the two fast ethernet links)? I am expecting
both the incoming traffic from the internet and the outgoing traffic from my
internal network are properly balanced on the two uplinks (don't really need
50%:50% balanced, but I think the setup should be able to fill up both of
the uplinks), and finally, if possible, firewall and some sort of failover
for the two uplinks are desirable.

I have thought about this setup:
fxp0: 10.123.123.100
fxp1: 10.123.123.101
em0: 10.123.123.102
but then thousands of question marks appeared in my head....
1) does freebsd allow assigning ip address in this way? 3 IPs in the same
subnet assigned to 3 different interfaces using the same netmask.
2) should I apply the multipath patch?
3) even if the multipath patch is applied, how should I configure the
default gateway?
4) suppose the gateway problem is solved. how would my isp's router know
which uplink to send the traffic down?

Could anyone spot me where did I get wrong? I have not carried out any
experiment yet, but my intuition tells me this would not work as expected.

Do I need IP addresses from different subnets, and perhaps do I need BGP4
peering with my ISP? Do I need different gateways (in different subnet?)
from my provider? What elses do I need from my ISP? Do I need to make any
changes to the IP address assignments to my existing internal computers?
and...if possible, could anyone pls give me an example in real great details
(at least including all the IP addresses of this router, the internal
computers and the ISP router).?
one thing more. besides getting traffic balanced on the two links, I would
also know if it was possible to add some high availability to the setup....

Thanks all in advance!


off topic: once upon a time when I was still in lab, I think I have tried to
use a cisco router with 3 ethernet interfaces to setup a router as described
above, but I don't remember the exact details (e.g. how did I assign the IPs
to different interfaces).

Sorry I was quite away from networking stuff for a while, pls forgive if
this question sounds stupid to you. :)

cheers,
mc.