[afnog] IP transit and Load Balancing

[Andy Davidson]

> On 9 Jun 2015, at 17:25, Joey ESQUIBAL <jesquibal at isoceltelecom.com> wrote:
> 
> May I ask your opinion and or best practice about having multiple IP transit to 4 different IPLC’s.
[…]
> I’m thinking of having two IP transit (which I think should be good already) and advertise specific prefix(es) on each peer.

Hi, Joey —

Since you are discussing inbound traffic engineering, I am assuming that you are trying to load balance for a heavy inbound network (actually, I know from our previous conversations that you are heavy inbound, but it is worth pointing out for people using this thread to learn about TE in the future).  Things like local preference alteration as mentioned in this thread do NOT help heavy inbound networks balance their traffic since local preference affects inbound prefixes and outbound traffic.

I have a strong recommendation to NOT announce difference prefixes to different transit providers, because doing so doubles the risk of failure.  If you have a provider failure on transit A *or* B, you suffer an outage given you are proposing not to announce your prefixes to both ISPs.

If you announce covering aggregates to both providers but longer prefixes to individual providers then this will make it hard to get traffic to flow to you via the shortest path (so you swap paying for bandwidth with paying for support calls and complaints!).

My advice is to try to understand, using Netflow or similar, who your largest inflows of traffic come from.  In my experience, heavy inbound networks have well over half of their traffic from under ten peer-ASNs.  Once these are understood and mitigated, it’s much simpler to deal with traffic engineering, as balancing for those larger senders will essentially wrap up the majority of your traffic.  My understanding of this reality is quite European slanted but I’d be really happy to take a look and send some advice about your top traffic originators either on list or off-list - and wearing no hats.

With best wishes,
Andy Davidson