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

[Paul Stewart]

Thanks again to everyone for your replies.... We're going to setup a
test link and see where it goes.  BGP is not an option... This concept
is driven by a customer who wants a connection via  us (as the ISP) and
also via another ISP for redundancy.....

All the best!

Paul
 

-----Original Message-----

> >

I wouldn't enable per-packet load-balancing on the interfaces, this can
sometimes foul up voip calls and video stuffs.  Especially since your
going out 2 different providers as one path will inevitably be longer
than the other and you'll get lots of of out of order packets.
With just 2 static routes it should use per-session or a hash-based
source ordering.  Where one session or source/dest pair will use one
link the next one will use the other link.  If you're just going to nail
up a single VPN session outbound you won't get any balancing but if you
have lots of destinations outbound you'll have better balancing.

Also note that after you get things up and running for a bit, if one
circuit goes down it can take a bit to come back to a balance as your
CEF cache gets re-ordered.  But hey, auto-failover is a heckuva lot
better than doing it manually!

Also, if you do end up with a BGP peer to each provider you can then
tweak your incoming traffic a bit better, as Frances said.  If you don't
use BGP then if both providers are roughly the same Tier level (ugh I
hate to mention tiers, I don't wanna start that discussion) your traffic
should somewhat even out over time.  Day to day you may see large
differences but over time it should be somewhat close.  The other side
of that is if you peer with say AT&T on one link and a customer of a
customer of a customer of UUnet/MCI/Verizon on the other you may see
traffic heavily favoring your ATT link inbound without some judicious
use of communities and prepends.  You'll just have to dive in and work
with it until you've gotten things somewhat close.

--chip

--
Just my $.02, your mileage may vary,  batteries not included, etc....