[149429] in North American Network Operators' Group
Re: IPv6 dual stacking and route tables
daemon@ATHENA.MIT.EDU (Owen DeLong)
Fri Feb 3 18:05:15 2012
From: Owen DeLong <owen@delong.com>
In-Reply-To: <4F2C3F18.3080804@gmail.com>
Date: Fri, 3 Feb 2012 15:02:23 -0800
To: -Hammer- <bhmccie@gmail.com>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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.
>=20
> "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."
>=20
> 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.
>=20
> Any guidance would be appreciated. Thanks.
>=20
>=20
>=20
>=20
> -Hammer-
>=20
> "I was a normal American nerd"
> -Jack Herer
>=20
>=20
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
