[Pool] Pool server monitoring 12ms offset
des at des.no
Tue Jun 8 18:11:42 UTC 2010
Chuck Swiger <cswiger at mac.com> writes:
> "hot potato" is a nice term, although RFC-2328 uses a fancier phrase,
> "Open Shortest Path First". :-) Although, in point of fact, OSPF is
> mostly used internally on large networks (within a single AS), and BGP
> is used for communication between different internetworks.
With my BGP admin hat on -
OSPF and BGP are different protocols with different purposes (OSPF is
used within an AS, BGP between ASes) based on different principles.
OSPF routers construct a complete graph of the network and and compute
the shortest path to every other node in the network, so they *do* make
globally-optimal rather than locally-optimal routing decisions which
*do* result in symmetric routes, provided that the connections between
routers are symmetric.
If, for instance, you have four OSPF routers arranged like this:
A --> B
D <-- C
where each connection is assymetric, with higher bandwidth / lower
latency in the direction of the arrow, a packet from A to C will be
routed through B, but a packet from C to A will be routed through D.
If, on the other hand, all connections are symmetric, it does not matter
whether a packet from A to C (or from C to A) is routed through B or D.
The latency will be the same both ways, regardless of whether the
response is routed through the same nodes as the request.
Still marginally on topic, since routing affects NTP performance (both
qualitative and quantitative).
Dag-Erling Smørgrav - des at des.no
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