On Feb 3, 2012, at 12:10 PM, -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.
> 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 reasoning was that DNS could potentially introduce some
> latency.
>
> "If you have a specific route to a AAAA record but a less specific route to
> an A record the potential is for the trip to take longer."
>
> That was the premise of the thread. I swear I googled it for 20 minutes to
> link before giving up. Anyway, can anyone who's been thru this provide any
> opinions on why or why not it is important to accept the full IPv6 table AND
> the full IPv4 table? I have the hardware to handle it I'm just not sure long
> term what the reasoning would be for or against. Again, I'm an end customer.
> Not a carrier. So my concern is (A) my Internet facing applications and (B)
> my users who eventually will surf IPv6.
>
> Any guidance would be appreciated. Thanks.
>
>
>
>
> -Hammer-
>
> "I was a normal American nerd"
> -Jack Herer
>
>
On a purely theoretical level, mores specific routes are always better than
default.
So, on a purely theoretical level:
IDEAL: Full routes, both protocols
Advantage: Most information available, theoretically best decisions
possible.
Disadvantage: Router cost rivals national debt of third-world country.
Second best: Full routes IPv6, default or partial routes IPv4
Advantage: Lots of information available, theoretically best IPv6
decisions.
Disadvantage: IPv6 might outperform IPv4 (not really a problem in most
cases)
Bigger disadvantage: Some IPv4 destinations might get blackholed from
time to time.
Third choice: Default both protocols
Advantage: At least you're still dual-stacked.
Disadvantage: All the disadvantages applied to IPv4 above now apply to
IPv6, too.
Worst choice: Don't implement IPv6
Advantage: Absolutely none.
Disadvantage: You can reach progressively less and less of the internet
over time.
However, the real answer is more complex than that. Sometimes the route that
looks the best in BGP might not actually be the best and so in some cases with
full tables you might send to the provider with the less effective path even
though default would have had you going via the more effective path. These
circumstances are rare, however, but, BGP has lots of knobs and depending on
how well you and your upstreams set those knobs, your experience can be
radically better or worse as a result.
If your trip to the A destination via default takes longer than your trip to
the AAAA destination via specifics, I'm not seeing a problem. Clients that have
IPv6 capability will get a better user experience and clients that don't have
IPv6 will get the same experience they got with default-based IPv4 prior to you
implementing IPv6.
Owen
