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
On Sat, 14 Sep 2002, Lupi, Guy wrote:
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 -----------------+ | Mike Leber Direct Internet Connections Voice 510 580 4100 | | Hurricane Electric Web Hosting Colocation Fax 510 580 4151 | | mleber@he.net http://www.he.net | +-----------------------------------------------------------------------+
On Sat, Sep 14, 2002 at 02:18:15PM -0400, Lupi, Guy wrote:
I was wondering how people tend to generate default routes to customers running bgp.
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 -- Jesper Skriver, jesper(at)skriver(dot)dk - CCIE #5456 Senior network engineer @ AS3292, TDC Tele Danmark One Unix to rule them all, One Resolver to find them, One IP to bring them all and in the zone to bind them.
participants (3)
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Jesper Skriver -
Lupi, Guy -
Mike Leber