Administrator Guide

Enabling Multipath
By default, the software allows one path to a destination. You can enable multipath to allow up to 64 parallel paths to a
destination.
You can configure the maximum number of parallel routes (multipath support) to a destination in BGP.
NOTE: Dell EMC Networking recommends not using multipath and add path simultaneously in a route reflector.
To allow more than one path, use the following command.
● Enable multiple parallel paths.
CONFIG-ROUTER-BGP mode
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.
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Border Gateway Protocol (BGP)