Distributing DNS servers

[Barry Margolin]

In article <37CC7CD7.FC68AF85 at swcp.com>, Bill Larson  <wllarso at swcp.com> wrote:
>I've been following this thread about DNS server failover capability
>and have been quite impressed.
>
>One question though, how quickly can OSPF or BGP routes be switched,
>and what triggers it?  Are you talking about an automatic detection
>process that triggers the routing table changes, or is it performed
>manually?  And, does the routing changes occur in seconds or minutes?

Once a router detects that a route is no longer available, switchover
occurs pretty rapidly.  The detecting router announces the change to its
peers, which recompute their routing tables and announce the changes to
their peers, and so on; this typically floods through an ISP backbone in
seconds (I've seen it take about 10-15 seconds to propagate across our
nationwide backbone).

The part that can be slow, though, is detecting the failure.  If a router
crashes, its peers won't detect that until they notice a timeout when
waiting for its periodic heartbeat messages.  But if something (either an
automated process or a human operator) makes a change to a routing table,
it will be announced immediately.

-- 
Barry Margolin, barmar at bbnplanet.com
GTE Internetworking, Powered by BBN, Burlington, MA
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