Question regarding load balancing

Barry Margolin barmar at genuity.net
Fri Jun 16 20:54:13 UTC 2000


In article <4.3.2.7.2.20000616152629.00bef720 at 64.20.73.233>,
Forrest Aldrich  <forrie at forrie.com> wrote:
>In the case of using a forwarder, how does this function actually work.  
>For example, we relay a query to our "forwarder" (as defined in
>named.conf), if the forwarder doesn't have a response, what happens at
>this point.  Do we send a query out to the internet ourselves or is the
>forwarder burdened with this task, relaying that response instead of
>what's in its cache.

When you query a forwarder, you set the Recursion Desired flag, so the
forwarder is expected to go out to the Internet.  Consider the most common
use of forwarders: when your server is behind a firewall that prevents it
from going out to the Internet itself.  If the forwarder didn't relay the
query out, how would you ever make an external query?

>In the case where you can define multiple IP addresses for the same DNS
>server, in an effort to load balance, how does this algorithm work.  
>Take for example a situation where you want to have multiple DNS servers
>in all of your edge POPs.  You would want each POP to use a DNS server
>that is closer in proximity.  I don't think the algorithm for load
>balancing really has anything like this.   

We use virtual addresses.  We have servers configured with the IP alias
4.2.2.1 in lots of different POPs, and the upstream router has a static
route for 4.2.2.1 pointing to the machine's real address.  This static
route is redistributed into our OSPF routing protocol, so a customer
querying 4.2.2.1 is automatically forwarded to the closest server.  If a
server is taken out of commission we remove the static route and they get
the next closest server (conceivably we could run gated on the servers and
get rid of the static routes, but our server administrators have chosen not
to do this).

-- 
Barry Margolin, barmar at genuity.net
Genuity, Burlington, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.



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