I was wondering how people tend to generate default routes to customers
running bgp. Is it from the aggregation router that customers are directly
connected to, or from one or more core/border routers? If one is using a
default route to null 0 on aggregation routers that maintain a full bgp
table (assuming that the full table represents all destinations on the
Internet, and therefore dumping traffic to a destination not in that table),
and assuming Cisco routers using the default-information originate command,
then as long as the router is up and it's bgp sessions with peers are up, it
is going to send the default route regardless of it's ability to forward
traffic to external destinations. The same goes for the default route
announced by a core/border router, if it's default is generated by the null
route. Is an assumption made that with a good network design, no router
will every be without valid routing information, with the exception of a
complete failure of the router?
Guy H. Lupi
I was wondering how people tend to generate default routes to customers
running bgp.
Typically you would only originate default via BGP to a customer that
isn't taking a full view.
neighbor 10.10.10.2 default-originate
neighbor 10.10.10.2 filter-list 9 out
ip as-path access-list 9 deny ^.*$
Is it from the aggregation router that customers are directly
connected to, or from one or more core/border routers?
In the example above the default originate is done via a specific BGP
session, so it isn't router wide on either core or border routers.
If one is using a default route to null 0...
I'll leave the rest of this for somebody else to answer.
Mike.
+----------------- H U R R I C A N E - E L E C T R I C -----------------+
Short answer: don't
Longer answer: To solve the exact problems you mention below,
only advertise a aggregate block of your own to this customer,
say x.x.0.0/16, then the customer will configure his device
something like
ip route 0.0.0.0 0.0.0.0 x.x.0.0
or
set routing-options static route 0.0.0.0/0 next-hop x.x.0.0 resolve
This will ensure that if the border router get's isolated, it will no
longer advertise x.x.0.0/16 to the customer, and the customer router can
choose a backup path.
/Jesper