On 2012-02-03 21:10 , -Hammer- wrote:
So, we are preparing to add IPv6 to our multi-homed (separate routers and carriers with IBGP) multi-site business. Starting off with a lab of course.
Dear "Hammer", Welcome to the 21th century. 2012 is going to "the year" (they claim, again ;) of IPv6 thus it is better to start before the big launch event that is this year, (of which there was also one back in in 2004: http://www.global-ipv6.org/ for the folks who have IPv6 for some time now ;) Better late than never some would say.
Circuits and hardware are a few months away. I'm doing the initial designs and having some delivery questions with the carrier(s). One interesting question came up. There was a thread I found (and have since lost) regarding what routes to accept. Currently, in IPv4, we accept a default route only from both carriers at both sites. Works fine. Optimal? No. Significantly negative impact? No. In IPv6, I have heard some folks say that in a multi-homed environment it is better to get the full IPv6 table fed into both of your edge routers. Ok. Fine. Then, The thread I was referring to said that it is also advisable to have the entire IPv4 table fed in parallel. Ok. I understand we are talking about completely separate protocols. So it's not a layer 3 issue.
The only advantage of more routes, in both IPv4 and IPv6 is that the path selection can be better. An end-host does not make this decision where packets flow, thus having a full route or not should not matter much, except that the route might be more optimal. No DNS involvement here yet. The trick comes with Happy-Eyeballs alike setups (especially Mac OSX Lion and up which does not follow that spec and in which it cannot be turned off either, which is awesome when you are debugging things...) Due to HE (Happy-Eyeballs) setups, which can differ per OS and per tool. Chrome has it's own HE implementation, thus if you run Chrome on a Mac you will have sometimes one sometimes another connect depending on if you are using Safari or Chrome for instance as Safari does use the system provided things. Ping will pick another again etc. It will be quite random all the time. The fun with the Mac OS X implementation is that it keeps a local cache of per-destination latency/speed information. If you thus have two default routes, be that IPv4 or IPv6, and your routers are swapping paths between either and thus don't have a stable outgoing path those latencies will vary and thus the pretty HE algorithms will be very confused. This is likely why your "source" recommended to have a full path, as per sub-prefix the path will become more stable and established than if you are doing hot-potato with two defaults. Greets, Jeroen