[c-nsp] BGP outbound loadsharing

[Alex Balashov]

Gert Doering wrote:
> Hi,
> 
> On Fri, Jan 23, 2009 at 04:58:31PM +0000, Alasdair McWilliam wrote:
>> For example, if you were downloading a full BGP table from both ISPs and
>> assigned local preference to some routes, traffic from a customer could
>> arrive on ISP1 and return traffic be sent via ISP2. Is this generally
>> considered to be acceptable or is it preferential for return traffic to be
>> routed the same ISP from which it came into your network?
> 
> It's generally considered to be pretty much unavoidable.

Yep.  Unless you want to do things that also bias incoming routing to 
ISP1 (whether or not the traffic went out that way), it's pretty much 
unavoidable.

Those things generally consist of AS path manipulation and 
community-based MED propagation (local preference doesn't leave the AS; 
  that's why it's a "local" preference).

The problem is that those things are shotgun solutions;  they weight the 
whole incoming path, not just those for traffic that went out ISP1 or ISP2.

-- Alex

-- 
Alex Balashov
Evariste Systems
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