[c-nsp] Fwd: Load Balancing two different ISP's

[Tim Franklin]

In respect of comments like:

> > Your sourcing packets with an IP address assigned from
> > ISP #1, out the interface to ISP#2.  Whereupon they will
> > get 1 hop then be killed by ISP #2's anti-spoof filter.

And:

> Gah! You're right, when working pretty much with only BGP folks all
> day I forgot that fact, just took it for granted.  However, if they
> have a /24 or larger space from ISP #1 they could get  ISP #2 to
> announce it for them and still wouldn't have to run BGP.  But your
> point is well made.

Are people missing:

> > > > We'll presume that the customer is running NAT of course....

?

If the OP has two publicly-addressed WAN links from two different providers,
two different NAT outside interfaces on the two WANs, and two corresponding
NAT overload / PAT configs, they can quite happily send traffic out of both
interfaces.

When it's going to ISP1, it'll be NAT'd to have an ISP1 source, likewise for
ISP2.

It doesn't give you a lot of options for balancing incoming traffic, beyond
putting both addresses in DNS and hoping, but you can get *something* out of
it.

Obviously ASN / address block / BGP gives much more control, but it's not
always an option, particularly if one or more of the ISPs you're trying to
connect to has you in the "residential" category.

Regards,
Tim.


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