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List:       linux-ha
Subject:    re: High-Availability on the network level
From:       Greg Freemyer <freemyer () NorcrossGroup ! com>
Date:       2002-02-04 19:16:14
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Alex,

I've read all the various responses to your e-mail, and I suspect they are all flawed \
when it comes to the real world.

BGP is the only real answer as far as I know, and you have to have a /18 subnet block \
to get that to work "in the real world".  

(i.e. a /18 is a block of 64 consecutive Class-C subnets.  Most backbone providers \
ignore BGP requests for smaller BGP updates!!!!  There is a handfull of standalone \
Class-Cs that they do support BGP updates on, but I understand that these class-Cs \
are very expensive to get your hands on and ARIN is definitely NOT still providing \
them.)

I have investigated this issue in the past.  There is even a $15K commercial product \
specifically made to handle this issue (http://www.fatpipeinc.com).

I talked to their technical people last summer.  They use a short TTL (Time To Live) \
in a DNS record, just as you propose.

Per the engineer there, it works okay for a lot of situations, but if the end-user of \
your service is connecting thru an ISP that ignores short TTLs, there is nothing you \
can do about.

AOL ignores all TTLs less than 48 hours.  Now AOL is huge part of the market, so if \
any of your end-users connect via them, the short TTL solution does NOT work.

For my customers that want to be able to do this, I recommend that put their servers \
into a high-quality co-location facility.  That facility should in turn have multiple \
feeds and participate in the BGP process.

I have worked with Level-3, Inflow, and E-DeltaComm to setup solutions like you want. \
They all claim to do this.  Inflow even has 3 feeds for each of their data centers \
and claims to test the BGP re-routing on a regular basis.  

The trouble is that they are all expensive, but prices have dropped drastically since \
2 years ago.  The most cost effective solution I know of today is E-DeltaComm (50 \
miles north of Atlanta).  They have a state of the art facility and will rent \
rackspace by the 1U, half-rack, full-rack, or the square foot if you need a bigger \
space.  Of course they all also charge for Internet access, and the smallest amount \
of bandwidth they will sell is 1Mbit.

BTW: If your interested in doing this in the Atlanta area, I can help you evaluate \
which co-location facility you might want to use.   That is part of what my company \
does for a living.

Greg Freemyer
Internet Engineer
Deployment and Integration Specialist
The Norcross Group
www.NorcrossGroup.com




 >>  Hi.

 >>  While usually this list receives question of high-availability regarging
 >>  redundant server configurations, i would like to ask about something else
 >>  :
 >>  after i made sure i have redundant server config, how do i make sure they
 >>  will always be accessible from the internet by the same dns name,
 >>  providing
 >>  i have 2 of more different internet connections, without using BGP ?

 >>  let's assume, that i have 2 ip ranges from my isp providers, 1.1.1.1/24
 >>  and
 >>  2.2.2.2/24, and the active server will always be accessible by 1.1.1.10
 >>  and
 >>  2.2.2.10. what when the 1.1.1.1 provider is up, the dns will point to
 >>  1.1.1.10 as my.server.com. when the 1.1.1.1 link goes down, i want the dns
 >>  to point to 2.2.2.10 as my.server.com

 >>  I assume i could use some dynamic dns service, like dyndns.org, to update
 >>  my
 >>  dns record - they have 1 minute expiration time on dns records, or i could
 >>  setup 2 dns servers serving my "server.com" zone, one will sit on 1.1.1.11
 >>  and the other on 2.2.2.11. my isp will always try to replicate dns zones
 >>  from the primay dns server 1.1.1.11, which will tell him that the address
 >>  of
 >>  my.server.com is 1.1.1.10, and if the isp is unable to get to 1.1.1.11 it
 >>  will go to the secondary server, 2.2.2.11, and it will tell him that
 >>  my.server.com address is 2.2.2.10

 >>  is there a better way to do that ?

 >>  Thanks.
 >>  Alex.


 >>  --------------------------------------------------------------------------
 >>  ----
 >>  Linux HA Web Site:
 >>  http://linux-ha.org/
 >>  Linux HA HOWTO:
 >>  
 >>  http://metalab.unc.edu/pub/Linux/ALPHA/linux-ha/High-Availability-HOWTO.h
 >>  tml
 >>  --------------------------------------------------------------------------
 >>  ----







------------------------------------------------------------------------------
Linux HA Web Site:
  http://linux-ha.org/
Linux HA HOWTO:
  http://metalab.unc.edu/pub/Linux/ALPHA/linux-ha/High-Availability-HOWTO.html
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