Brocade Communications Systems Layer 3 Routing Configuration ICX 6650 - Manual (Page 335)

Brocade ICX 6650 Layer 3 Routing Configuration Guide 317
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Optional BGP4 configuration tasks
Brocade(config-bgp-router)#med-missing-as-worst
Syntax: [no] med-missing-as-worst
NOTE
This command affects route selection only when route paths are selected based on MED
comparison. It is still possible for a route path that is missing its MED to be selected based on other
criteria. For example, a route path with no MED can be selected if its weight is larger than the weights
of the other route paths.
Route reflection parameter configuration
Normally, all the BGP routers within an AS are fully meshed. Each of the routers has an IBGP
session with each of the other BGP routers in the AS. Each IBGP router thus has a route for each of
its IBGP neighbors. For large autonomous systems containing many IBGP routers, the IBGP route
information in each of the fully-meshed IBGP routers can introduce too much administrative
overhead.
To avoid this problem, you can hierarchically organize your IGP routers into clusters:
• A cluster is a group of IGP routers organized into route reflectors and route reflector clients. You
configure the cluster by assigning a cluster ID on the route reflector and identifying the IGP
neighbors that are members of that cluster. All the configuration for route reflection takes
place on the route reflectors. The clients are unaware that they are members of a route
reflection cluster. All members of the cluster must be in the same AS. The cluster ID can be any
number from 0 through 4294967295. The default is the router ID, expressed as a 32-bit
number.
NOTE
If the cluster contains more than one route reflector, you need to configure the same cluster ID
on all the route reflectors in the cluster. The cluster ID helps route reflectors avoid loops within
the cluster.
• A route reflector is an IGP router configured to send BGP route information to all the clients
(other BGP4 routers) within the cluster. Route reflection is enabled on all Brocade BGP4
routers by default but does not take effect unless you add route reflector clients to the router.
• A route reflector client is an IGP router identified as a member of a cluster. You identify a router
as a route reflector client on the router that is the route reflector, not on the client. The client
itself requires no additional configuration. In fact, the client does not know that it is a route
reflector client. The client just knows that it receives updates from its neighbors and does not
know whether one or more of those neighbors are route reflectors.
NOTE
Route reflection applies only among IBGP routers within the same AS. You cannot configure a cluster
that spans multiple autonomous systems.
Figure 26 shows an example of a route reflector configuration. In this example, two Layer 3
switches are configured as route reflectors for the same cluster. The route reflectors provide
redundancy in case one of the reflectors becomes unavailable. Without redundancy, if a route
reflector becomes unavailable, its clients are cut off from BGP4 updates.