redirecting overseas requests to local servers

[Barry Margolin]

In article <19990907234535.C5150 at space.net>,
Markus Stumpf  <maex-bind-users at Space.Net> wrote:
>On Mon, Sep 06, 1999 at 05:42:40PM -0700, Patrick Greenwell wrote:
>> > > > > UltraDNS provides a service where you can reach the *topologically*
>> > > > > closest server according to BGP. http://www.ultradns.com.
>> Basically: (beware, bad ascii art follows)
>> 
>>                                        
>> +--------+      +-----+       +-----+        +-----+      +------+
>> | client |<---->| IGP |<----->| BGP |<------>| BGP |<---->|server|
>> +--------+      +-----+       +-----+<-      +-----+      +------+
>>                                        \ 
>>                                          \ 
>>                                            \   +-----+      +------+ 
>>                                              ->| BGP |<---->|server| 
>>                                                +-----+      +------+
>> 
>
>Ok, so far so good.
>Routers exchange routes via BGP to get their routing straight, but
>(maybe I am too dumb to understand that ...)
>why for heavens sake, would a DNS SERVER want to know anything about
>routing (if it isn't running on a multihomed machine itself).

So that it can give out different answers depending on proximity in the
network.  Consider the following diagram:

 +--------+      +-----+       +-----+        +-----+      +------+
 | client1|<---->| IGP |<----->| BGP |<------>| BGP |<---->|serv1 |
 +--------+      +-----+       +-----+        +-----+      +------+
                                  ^              ^
                                  |              |
                                  v              v
 +--------+      +-----+       +-----+        +-----+      +------+ 
 | client2|<---->| IGP |<----->| BGP |<------>| BGP |<---->|serv2 | 
 +--------+      +-----+       +-----+        +-----+      +------+
                                      
When client1 looks up www.company.com it should return the address of
serv1, but when client2 looks up www.company.com it should return the
address of serv2.

>To be honest I never really understood what "topology" could be used
>for in a serious way in bind.
>A few days ago I saw an email where someone claimed they had "dramatically"
>increased their DNS answer speed by heavily using the topology feature.
>On the other side I remember a post by Mark Andrews in this forum not to
>long ago where he explained that bind keeps its own statistics on
>reachability and speed of answers (or does this only hold for root DNS
>servers?) and the choosing algorithm is based on this data.
>So, if I do not restart bind every hour or so, why would I want bind
>to know about routing and topology?

BIND can only build up this information dynamically by actually querying
all the servers.  In cases where the server operator knows a priori that
certain networks are much closer than others, he can configure explicit
topology statements.

If you don't feel like using it, you don't have to.

-- 
Barry Margolin, barmar at bbnplanet.com
GTE Internetworking, Powered by BBN, Burlington, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
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