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9.3 | ![]() |
Configuring BGP | |
9.3.7 | ![]() |
BGP continuity inside an AS |
BGP does not advertise routes learned by way of IBGP peers to other
IBGP peers. If BGP did, BGP routing inside the AS would present a
dangerous potential for routing loops. For IBGP routers to learn about
all BGP routes inside the AS, they must connect to every other IBGP
router in a full IBGP mesh. This full mesh needs to be only logical,
not physical. In other words, as long as the IBGP peers can connect to
each other using TCP/IP, a logical full mesh can be created even if
the routers are not directly connected.
Figure However, routing in this scenario is not complete. EBGP routes
learned by way of San Jose will not be given to Los Angeles, and EBGP
routes learned by way of Los Angeles will not be given to San Jose.
This is because the San Francisco router will not advertise IBGP
routes between San Jose and Los Angeles. What is needed is an
additional IBGP connection between San Jose and Los Angeles. This
connection is shown as a dotted line.
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