Newbies Question: Do I really need to sacrifice Prefix-aggregation to do BGP Load-sharing? (the case of Multi-homed + Multi-routers + Multi-upstreams)

Jay Hennigan jay at
Wed Oct 19 18:32:29 UTC 2022

On 10/18/22 23:27, Pirawat WATANAPONGSE via NANOG wrote:
> Dear Guru(s),
> My apologies if these questions have already been asked;
> in that case, please kindly point me to the answer(s).
> I hope the following information sufficiently describes my current 
> "context":
> - Single customer: ourselves
> - One big IPv4 block + one big IPv6 block
> - Native Dual-Stack, Non-tunneling
> - Non-transit (actually, a “multi-homed Stub”)
> - “All-green” IRR & RPKI registered (based on IRRexplorer report)
> - Fully-aggregated route announcement (based on CIDR report)
> - Two (Cisco) gateway routers on our side
> - Two upstreams (See the following lines), fully cross-connected to our 
> gateways
> - One (pure) commercial ISP
> - One academic consortium ISP (who actually uses the above-mentioned 
> commercial ISP as one of its upstreams as well)
> My current “situation”:
> - All inbounds “flock” in through the commercial ISP, overflowing the 
> bandwidth;
> since (my guess) the academic ISP also uses that commercial ISP as its 
> upstream, there is no way for its path to be shorter.

Many of the commercial ISPs will accept communities allowing you to 
fine-tune how your advertisements are propagated, some of which are 
quite granular. This is the best method to do so. Prepending can help 
but your commercial upstream will by default prefer your route as a 
direct customer regardless of prepending. used to have a comprehensive listing of many transit 
providers and the communities they accept but it's returning 403 
forbidden now. Ask your upstream for the communities they accept.

Jay Hennigan - jay at
Network Engineering - CCIE #7880
503 897-8550 - WB6RDV

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