Administrator Guide

maximum-paths {ebgp | ibgp} number
Configure the following parameters:
• ebgp: Enable multipath support for external BGP routes.
• ibgp: Enable multipath support for internal BGP routes.
• number: Maximum number of parallel paths. The range is from 2 to 64.
DellEMC# configure terminal
DellEMC(conf)# router bgp 400
DellEMC(conf-router_bgp)# maximum-paths ibgp 5
DellEMC(conf-router_bgp)# exit
In the above example configuration, the maximum number of parallel internal BGP routes is set to 5, so that only 5 routes can be installed
in a routing table.
The show ip bgp network command includes multipath information for that network.
Route Reflectors
Route reflectors reorganize the iBGP core into a hierarchy and allow some route advertisement rules.
NOTE: Do not use route reflectors (RRs) in the forwarding path. In iBGP, hierarchal RRs maintaining forwarding plane
RRs could create routing loops.
Route reflection divides iBGP peers into two groups: client peers and nonclient peers. A route reflector and its client peers form a route
reflection cluster. Because BGP speakers announce only the best route for a given prefix, route reflector rules are applied after the router
makes its best path decision.
• If a route was received from a nonclient peer, reflect the route to all client peers.
• If the route was received from a client peer, reflect the route to all nonclient and all client peers.
To illustrate how these rules affect routing, refer to the following illustration and the following steps. Routers B, C, D, E, and G are
members of the same AS (AS100). These routers are also in the same Route Reflection Cluster, where Router D is the Route Reflector.
Router E and H are client peers of Router D; Routers B and C and nonclient peers of Router D.
Figure 25. BGP Router Rules
1. Router B receives an advertisement from Router A through eBGP. Because the route is learned through eBGP, Router B advertises it
to all its iBGP peers: Routers C and D.
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.
Border Gateway Protocol (BGP)
203