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I would argue that one can generally safely add
information to his or her router's RIB (such as adding a
local preference, weight, or advertising with prepends to
direct traffic toward a better performing, less utilized,
or lower cost peer), but that removing information from a
router's RIB always comes at some cost (and some may find
this cost perfectly acceptable).<br>
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<div>One needs to remember that removing information from RIB
is how BGP works. If you have the common setup of two BGP
edge routers, each with a directly connected transit
provider link, the routers will only tell the other one
about the routes it actually uses. Neither router has a
complete view.</div>
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I manage a network like you describe: Two BGP edge routers, both
routers accept a full eBGP feed from transit, both share routing
information via iBGP. Both edge routers in my network have a
complete view. If one transit provider is down or there is an
upstream peering change, both still have a complete view. The only
time they wouldn't have a complete view is during convergence or
when there is a simultaneous outage of both transit providers at
different physical facilities. <br>
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I could certainly use a default route (configured statically or
received via BGP) instead, but that reduces my network's ability to
make informed decisions. When one of my upstream transit providers
is performing maintenance and loses a peer, I want that to be
reflected in my routing so that traffic can be directed via the
shortest path. When my transit provider's edge router loses upstream
connectivity, but maintains connectivity to my equipment, I want
that reflected in my routing so that traffic doesn't go towards the
path that leads to the bit bucket. I can't detect those conditions
and route around them if my router only has a default route.<br>
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