IPv6 dual stacking and route tables

Cameron Byrne cb.list6 at gmail.com
Fri Feb 3 20:28:01 UTC 2012

On Fri, Feb 3, 2012 at 12:10 PM, -Hammer- <bhmccie at gmail.com> 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.

Well.  I don't really follow the above text.

But, the principle is the same for IPv4 or IPv6.  If you take a full
or partial table, your router can make a better choice than just
getting default  (only maybe, BGP is never guaranteeing anything about

That said, in v6, it is a little bit more important, IMHO, to take the
ISP routes instead of just a default since the v6 peering is not as
robust out on the Internet.  There are still turf wars going on or
some SPs are still not peering IPv6 in all the places they peer for
IPv4.  Less peering = longer latency. But, this situation has improved
dramatically in the last 12 months.

In the end, my guidance is to take "provider routes" or "customer
route" + default.  This helps your router make an educated guess
without absorbing all the churn and gunk that a full BGP feed hits
your router with.  Make the SP trim those routes on their side so you
don't see it.

> -Hammer-
> "I was a normal American nerd"
> -Jack Herer

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