[76606] in North American Network Operators' Group
Re: Anycast 101
daemon@ATHENA.MIT.EDU (William Allen Simpson)
Fri Dec 17 09:29:34 2004
Date: Fri, 17 Dec 2004 09:27:25 -0500
From: William Allen Simpson <wsimpson@greendragon.com>
To: NANOG list <nanog@nanog.org>
In-Reply-To: <03ABCE4F-5024-11D9-B673-000A95CD987A@muada.com>
Errors-To: owner-nanog-outgoing@merit.edu
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
Key fingerprint = 17 40 5E 67 15 6F 31 26 DD 0D B9 9B 6A 15 2C 32
