Re: Anycast 101

[William Allen Simpson <wsimpson () greendragon com>]

Iljitsch van Beijnum wrote:

> On 17-dec-04, at 3:06, Steve Gibbard wrote:
>
> > > under some very
> > > specific circumstances it can also happen with per packet load
> > > balancing.
>
> > You're misunderstanding how per-packet load balancing is generally used.
>
>
> I wasn't saying anything about how per packet load balancing is 
> generaly used, the point is that it's possible that subsequent packets 
> end up at different anycast instances when a number of specific 
> prerequesites exists. In short: a customer must pplb across two 
> routers at the same ISP, and each of those routers must have different 
> preferred paths to different anycast instances. This isn't going to 
> happen often, but it's not impossible, and it's not bad engineering on 
> the customer's or ISP's part if it does, IMO.
You're wrong.  That's VERY bad engineering!

PPLB requires 2 routers, one at each end of the link bundle. 

More than 1 router at any end will lead to a lot more problems than
anycast, including multicast and any stateful protocol (like TCP).

For one thing, the load balancing will be only in 1 direction, and will
lead to congestion in the reverse path....  Self defeating.

--
William Allen Simpson
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