What's the point of prepend communities?

Jason Lixfeld jason+nanog at lixfeld.ca
Thu Oct 26 17:58:32 CST 2017


Of all the ISPs that I am familiar with that have a BGP community structure usable by their peering partners and/or downstream customers, among other things, they allow the customer to signal the ISP to prepend their own AS to the as-path of a particular prefix announcement.

What functionality does a provider prepend support that is otherwise lost in the absence of such a feature, but all the while, the customer would be able to prepend their own AS to the same prefix announcement anyway?

Is this a relic from before ISPs allowed for local preference adjustment, or is there actually a use case for this?


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