Multihoming/Multi-ISP question

[Lance Westerhoff]

Hi Andrew-

I've been playing with it a bit more, and the odd thing is, I can get  
it to work depending upon which IP address is placed on which NIC  
(always a good sign I know!).

So if I put IP1 on NIC1 and IP2 on NIC2 and then put NIC1 ahead of  
NIC2 on the list in network control panel, it works!  Pings to both  
NICs from an outside source return just fine...

The fun begins when I shift NIC2 ahead of NIC1 on the list...  When I  
do that, pings from the outside are only answered when I ping NIC2  
and any pings to NIC1 are dropped.

Interesting:

NIC1 = Builtin port on old dual-G4

NIC2 = Farralon (sp?) Card

NIC3 = Netgear card

In terms of the default gateway, I thought of that too since I could  
see the pings packets being received on the second NIC, but they  
weren't sending back out correctly.  Unfortunately, I had hoped that  
there was a "quick fix" I could use for the time being.  Thankfully,  
the NIC1/NIC2 ordering I noted above seems to work for now...I only  
really need it for a few days so I can accept the less-then-robust  
status for now I guess....It is weird though!

-Lance



On Sep 7, 2007, at 2:56 PM, Andrew Oliver wrote:

> you're missing the fact that you can only have one default gateway.
>
> ALL non-local traffic (or, at least, traffic that doesn't have a  
> static route defined) will go out through the default router address.
>
> This means that you can not have two active, public IP addresses on  
> a server - traffic may come in on the second link, but it's going  
> to go out of the first link, and that is going to break most models.
>
> In short, what you want can't be done easily without a proper  
> router between your server and the outside world.
> In theory you can use source routing (look at the source of the  
> packet to decide which router address to send it back through), but  
> I haven't heard of any successful implementations on Mac OS X.
>
> Andrew
> :)
>
> On Sep 7, 2007, at 11:22 AM, Lance Westerhoff wrote:
>
>>
>> Hello-
>>
>> We recently switched from one ISP to another, and as our domain  
>> and whatnot are changed over, I was hoping to listen to both IPs  
>> at once.  I have a Mac OS X Server (10.4) with three working  
>> ethernet cards: one for each of the internet connections, and one  
>> for an internal network.  The machine also acts as our DHCP/NAT  
>> box for our small office network.  Again, all of this works except  
>> one thing: I can't listen to both internet connections at once.   
>> Basically, if I set one up in the Network Control Panel as the top  
>> connection, the other internet connection goes down.  I figured  
>> that one of the interfaces is down, but according to ifconfig they  
>> are both up but I haven't been able to use ifconfig to have accept  
>> packets from both.  I must be missing something stupid.  I have  
>> spent hours looking around to no avail.  It doesn't really seem to  
>> be an IPalias situation since technically it isn't an alias to  
>> another interface.  When I try to set up an alias using ifconfig,  
>> no matter what I do (to either interface) seems to do the trick.
>>
>> Unfortunately, this is just a temporary need until everything gets  
>> switched over/tested.  I've set up a similar situation without  
>> trouble on Linux before so I can't imagine OS X Server can't do  
>> the same thing!
>>
>> Thank you for your time and insights!
>>
>> -Lance
>>
>>
>>
>>
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>
>