[28809] in North American Network Operators' Group
Re: IGPs and services?
daemon@ATHENA.MIT.EDU (ww@shadowfax.styx.org)
Wed May 17 01:40:04 2000
From: ww@shadowfax.styx.org
To: nicholas harteau <nrh@ikami.com>
Cc: nanog@merit.edu
In-Reply-To: Your message of "Wed, 17 May 2000 00:09:23 CDT."
<20000517000923.C8187@execpc.com>
Date: Wed, 17 May 2000 01:34:10 -0400
Message-Id: <20000517053411.3F00D7469@shadowfax>
Errors-To: owner-nanog-outgoing@merit.edu
>>>>> "nicholas" == nicholas harteau <nrh@ikami.com> writes:
nicholas> I'm looking for some advice on IGP tricks such that we
nicholas> can give out the same IPs for a specific service
nicholas> (say...DNS) to all of our customers despite geography
nicholas> and have my IGP route those packets to a regional
nicholas> server, thus accomplishing some inherent level of load
nicholas> balancing, and even eventually returning data based on
nicholas> client geography.
Assign a unique (or several uniqe...) address that the customers will
use, say 1.1.1.1. Configure this address onto the loopback interface
of each of the servers as a secondary address. Have the host run a
routing protocol (OSPF lends itself to this nicely since the area
construct us usefull) and have it inject 1.1.1.1/32 into the IGP.
Then arrange so that the IGP will direct all traffic to the server
within the the same area as the source of the traffic. There are
several ways to do this:
- filter routing updates for 1.1.1.1/32 at the area border
routers. This is not so good as it would probably be good to redirect
traffic to a server in another area should the local one go down for
some reason.
- with OSPF, configure the cost parameter on inter area links to a
value larger than that associated with any intra area path -- this
will make sure that a routes from one area are always preferred over
inter area routes. In fact I'm pretty sure OSPF does this automatially
anyways, but it's nice to have things explicitly configured like this
-- your "serving" area needn't necessarily correspond with an OSPF
area in this case (a single OSPF area may be divided into two
"serving areas" , for example).
You can achieve load balancing in a more fault tolerant manner in this
way too -- say you want to load balance across two web servers, but
you want one to take over all of the load should the other
fail. Configure the dns to round robin on 1.1.1.2 and 1.1.1.3, say and
configure both of these addresses as aliases on the loopback
interfaces of both servers. The first server advertises the first
address with a lower cost than the second and the second does the
reverse. The difference in cost should be greater than the cost
associated with the best path between the servers.
What is the general feeling about running routing protocols on
web/dns/mail servers?
Cheers,
-w
--
Will Waites \________
ww@shadowfax.styx.org\____________________________
Idiosyntactix Ministry of Research and Development\
