I'll attack these one at a time below
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On 8/6/00 at 7:10 AM Stephane Wantou Siantou wrote:
>I need help with the following exam objectives:
>1) Describe BGP synchronization
The rule of synchronization states that no BGP router will advertise a networks
reachability until all other routers within the same AS have learned about the network
via an IGP (Interior Gateway Routing protocol). Synchronization is designed to ensure
that transit AS's (those that pass traffic that is neither originated from nor
destined to themselves) do not accept traffic in via one router and not be able to
proper route the traffic due to other routers not possessing the same routing
information. Another way of looking at is that IBGP routers do not advertise routes
learned from other IBGP routers to other IBGP routers. What that means is, each IBGP
router must learn about routes directly from a source instead of by way of a third
party within the AS.
>2) Describe the scalabilitity problems associated with internal BGP
In an AS, by default, all IBGP routers need to know about each other via neighbor
statements to ensure route consistency among other things. This is driven by the
above rule stating that IBGP routers will not pass routing information from one to the
next, but must instead speak directly with each source. This is great with a few
routers, but as more are added, the sheer number of neighbor statements and processing
power required to handled the individual relationships becomes overwhelming.
>3)Explain and configure BGP route reflectors
Route Reflectors serve to assist in the above salability issue. Instead of having
every IBGP router peer with every other, certain routers are designated as route
reflectors. These routers are able to pass route information learned from one IBGP
router to others. In this type of configuration, a number of reflector clients can
simply be pointed at designated reflector servers and everything works well.
Here is a sample config.
router bgp 100
neighbor 1.1.1.1 remote-as 100
neighbor 1.1.1.1 route-reflector-client
neighbor 2.2.2.2 remote-as 100
neighbor 2.2.2.2 route-reflector-client
It should be noted that you do not have to configure a router as a route reflector
server, it becomes one automatically when clients point at it.
The following link from Cisco explains all of this 10 times better and in way more
detail.
http://www.cisco.com/univercd/cc/td/doc/cisintwk/idg4/nd2003.htm#13629
Its also been a while since I thought about this stuff so point out where i'm mistaken
if i've misrepresented anything!
Hope this helps!
Peter V
http://www.cisco.com/univercd/cc/td/doc/cisintwk/idg4/nd2003.htm#13629
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