mailing list archives
Re: Disaster recovery using as-prepend?
From: Warren Kumari <warren () kumari net>
Date: Thu, 16 Feb 2006 12:29:29 -0800
Part of the question is how bad it is for you if you DO get any
traffic to your backup datacenter, the connectivity between the
datacenters and the datacenters connectivity to the rest of the world.
Assuming that you do not have good connectivity between datacenters
and that the datacenters have different connectivity to the outside
While pre-pending should get almost all of your traffic away from
your backup DC, you cannot guarantee that it will not get any traffic
while the primary is still up.
If your primary is connected to ISP_A and the backup is connected to
ISP_B, customers connected to ISP_B MAY still flow to your backup DC
(ISP_B will probably set local preference on all customer routes -
you should be able to override this behavior with communities but not
all providers support this (or honor it 100% of the time!))
Announcing a more specific from the primary is likely to work
basically all the time (assuming a) your announcement is not too long
to be listened to, b) ISP_A and ISP_B don't lose connectivity between
themselves). This is not particularly polite however...
Another option is just not to announce the backup datacenter until
the primary one goes away - see if you can do something like BGP
Conditional Advertisement (or your vendor's version of the same).
Depending on just how bad having request arrive at the backup
datacenter will drive just how paranoid you ned to be - if having
your backup get traffic is going to make databases unhappy, etc then
you MIGHT even want to consider a manual only failover - if your
primary datacenter has a 20 second blip, the pain of dealing with
requests that hit the backup during those 20 seconds MAY be greater
than just being unavailable for 20 seconds... It all depends on your
business, applications, etc, but prepending alone might not be the
way to go.
On Feb 16, 2006, at 6:56 AM, Christopher J. Pilkington wrote:
My apologies if this question doesn't belong here.
We have a PI /24 we'd like to advertise out of our primary data center
for production use. (Well, actually, we'll be advertising a more
specific from our /21 assignment, so already not too friendly... but I
We have a disaster recovery site which will have a clone of the myriad
production servers. We'd like to fail over to that site
I'm thinking advertising the same prefix and just doing several
as-prepends. However, now I'm not sure if this is a polite thing to
do or not.
Someone mentioned to me something with MEDs, but as soon as that term
was used, I started twitching, and couldn't follow the conversation.
Would a "good netizen" use the as-prepend method? Or am I missing a
simpler/more polite solution?