Administrator Guide
2. Router C receives the advertisement but does not advertise it to any peer because its only other peer is Router D, an iBGP
peer, and Router D has already learned it through iBGP from Router B.
3. Router D does not advertise the route to Router C because Router C is a nonclient peer and the route advertisement came
from Router B who is also a nonclient peer.
4. Router D does reflect the advertisement to Routers E and G because they are client peers of Router D.
5. Routers E and G then advertise this iBGP learned route to their eBGP peers Routers F and H.
Configuring BGP Route Reflectors
BGP route reflectors are intended for ASs with a large mesh; they reduce the amount of BGP control traffic.
NOTE: Dell EMC Networking recommends not using multipath and add path simultaneously in a route reflector.
With route reflection configured properly, IBGP routers are not fully meshed within a cluster but all receive routing information.
Configure clusters of routers where one router is a concentration router and the others are clients who receive their updates
from the concentration router.
To configure a route reflector, use the following commands.
● Assign a cluster ID or an IP address to a router reflector cluster.
CONFIG-ROUTER-BGP mode
bgp cluster-id ip-address | number
○ ip-address: IP address as the route reflector cluster ID.
○ number: A route reflector cluster ID as a number from 1 to 4294967295.
You can have multiple clusters in an AS. When a BGP cluster contains only one route reflector, the cluster ID is the route
reflector’s router ID. For redundancy, a BGP cluster may contain two or more route reflectors. Without a cluster ID, the
route reflector cannot recognize route updates from the other routes reflector within the cluster.
● Configure the local router as a route reflector and the specified neighbors or peer group as members of the cluster.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | ipv6-address | peer-group-name} route-reflector-client
When you enter this command for the first time, the router configures as a route reflector and the specified BGP neighbors
configure as clients in the route reflector cluster. When you remove all clients of a route reflector using the no neighbor
route-reflector-client command, the router no longer functions as a route reflector. When you enable a route reflector,
Dell EMC Networking OS automatically enables route reflection to all clients. To disable route reflection between all clients in
this reflector, use the no bgp client-to-client reflection command in CONFIGURATION ROUTER BGP mode. All
clients must be fully meshed before you disable route reflection.
To view a route reflector configuration, use the show config command in CONFIGURATION ROUTER BGP mode or the
show running-config bgp in EXEC Privilege mode.
Enabling Route Flap Dampening
When EBGP routes become unavailable, they “flap” and the router issues both WITHDRAWN and UPDATE notices.
A flap is when a route:
● is withdrawn
● is readvertised after being withdrawn
● has an attribute change
The constant router reaction to the WITHDRAWN and UPDATE notices causes instability in the BGP process. To minimize this
instability, you may configure penalties (a numeric value) for routes that flap. When that penalty value reaches a configured
limit, the route is not advertised, even if the route is up. In Dell EMC Networking OS, that penalty value is 1024. As time passes
and the route does not flap, the penalty value decrements or is decayed. However, if the route flaps again, it is assigned another
penalty.
The penalty value is cumulative and penalty is added under following cases:
● Withdraw
● Readvertise
Border Gateway Protocol (BGP)
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