[c-nsp] BGP vs PepLink / AT&T metrics on BGP

[Jay Hennigan]

Rogelio wrote:
> For a campus environment, I've got two WAN connections, one through 
> Charter (30Mbps) and one through AT&T (50 Mbps). For load balancing, I 
> am evaluating whether or not to use BGP or some sort of load sharing 
> device, like PepLink.
> 
> With BGP, I am told that my AT&T pipe may get saturated quicker, as 
> their metrics are better.  Anyone else have problem?  Or does anyone 
> have any suggestions for someone who is new to BGP in this sort of 
> situation?

BGP requires more clue on your part and more care.  It also requires 
that you have IP space that both providers are able and willing to 
advertise.  Best is space allocated to you by your RIR, and that you 
obtain an AS number from your RIR.  Justifying IP space can be an issue 
for smaller networks.  As people multi-home with BGP, the burden they 
place on the rest of the Internet increases.  The rest of the world will 
now need to allocate memory and CPU cycles to keep track of how to reach 
you, not just how to reach AT&T and Charter.

BGP has a big advantage in terms of control and simplifies the setup of 
resources on your end that must be available should either provider 
fail, as the same IP addresses are reachable through either provider. 
Routing will be more optimal with BGP than with other load sharing 
devices if it is set up and maintained properly.

With BGP, it is far easier to control how traffic leaves your network 
than how it arrives, so if your goal is to avoid saturating either pipe 
outbound, this isn't usually an issue if you have a relatively good 
diversity of remote endpoints.  Controlling traffic inbound is more of 
an art, but achieving a relatively good balance according to your pipe 
sizes is usually quite doable, especially if your upstreams accept 
communities from you to influence your traffic leaving their networks. 
(AT&T does, not sure about Charter).

Obviously, if either pipe goes down and your traffic exceeds the 
bandwidth of the remaining one, you'll get congestion regardless of the 
method used to load-share.

--
Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
Impulse Internet Service  -  http://www.impulse.net/
Your local telephone and internet company - 805 884-6323 - WB6RDV