When did most larger ISPs start weighting their peer ISP connections?

[derek.small]

I've been a CCIE for over 20 years and have connected a few dozen companies redundantly via BGP to the Internet over that time.  It's been about 5 years since the last time I brought up redundant BGP routed ISP connections, and maybe I didn't do as much checking on looking glass routers the last time, but I'm seeing something I haven't seen (much) in years past.  For this current customer, I'm seeing looking glass routers on most ISPs are now using local-pref to direct traffic through a given peer ISP, regardless of AS path length.  You used to be able to do AS prepends to get traffic to come in more from ISP-A, than from ISP-B.  Now there are very few ISPs that have equal cost local-prefs from peer ISPs so your traffic from ISP-C will ALWAYS use ISP-A to come in.  While ISP-D will always use ISP-B to come in.  I know some smaller ISPs have done this because they didn't have fat connections to all their peer ISPs, but I never used to see this on the back-bone providers.  Anyone know what is driving this?  I'm assuming it's either net-neutrality or a response to massive DDoS attacks, but neither seems to be a good enough reason for this biasing of ISP-to-ISP peering on such a wide scale.

[MHM Cisco World]

Can you more elaborate.

[Harold Ritter]

Hi @derek.small ,

I have been working with service providers for almost 25 years and this has always been a very common practice. Here's the route selection priority they normally apply:

Customers preferred over Peers preferred over Transits.

The rational is the following:

Customers pay for traffic they send and receive.

Peers peering session are normally free (might not be in some cases)

Transits will charge for traffic you send and receive from them.

So, it makes sense from a SP economical standpoint to follow the Customers, Peers, Transits order.

This is the reason AS-Path prepending might not always do the job. Some alternatives are BGP conditional advertisements or advertising a shorter prefix (/23 vs /24 for instance) through the preferred SP.

Regards,