Brocade Multi-Service IronWare Routing Configuration Guide (Supporting R05.6.00) - Manual (Page 50)

22 Multi-Service IronWare Routing Configuration Guide
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BGP router reflector
However, in certain configurations it is possible that the total number of preferred BGP4 routes may
exceed the RTM route table size limit. Therefore, some preferred BGP4 routes may not be installed
in the RTM, and the BGP router is not able to forward traffic correctly for those BGP4 routes. Those
BGP4 routes are not considered as the best BGP4 routes, and are not advertised to other BGP4
neighbors because traffic miss-forwarding or packet drop can occur.
When a BGP router is configured as only a route reflector server, and is not placed directly in the
forwarding path, it is possible to mark all preferred BGP4 routes as the best routes to be advertised
to other BGP4 neighbors even if the routes are not installed in the RTM. To support the behavior of
a BGP router as a route reflector server in such a scenario, use the always-propagate command
and the rib-route-limit command. The following section,
“Configuring BGP router reflector” describes
these commands in more detail.
NOTE
The always-propagate command and the rib-route-limit command are supported on Brocade MLX
series, Brocade NetIron XMR, Brocade NetIron CER, and Brocade NetIron CES devices.
Configuring BGP router reflector
The always-propagate command enables a router to mark a preferred BGP4 route not installed in
the RTM as the best route, and advertise the route to other BGP4 neighbors. The same process for
outbound route policy continues to apply to all best BGP4 routes. The rib-route-limit command
limits the number of BGP4 Routing Information Base (RIB) routes that can be installed in the RTM.
The RTM must be able to reserve enough entries for Interior Gateway Protocol (IGP) routes because
the IGP routes are required by BGP4 to resolve BGP4 next-hop entries. If the RTM is not able to
reserve enough entries for IGP routes, BGP4 RIB routes can fill the entire RTM with only BGP4 route
entries. The rib-route-limit command enables IGP and BGP4 route entries to be installed in the
RTM.
NOTE
The always-propagate command and the rib-route-limit command are configurable in any order
under the BGP4 address family configuration level.
Perform the following steps to advertise a preferred BGP4 route not installed in the RTM.
1. Configure a BGP4 unicast route. Enter a command such as the following.
Brocade(config-bgp)#address-family ipv4 unicast
Syntax: address-family ipv4 unicast [vrf vrf-name]| ipv4 multicast | ipv6 unicast | ipv6
multicast
NOTE
To configure a BGP4 unicast route for a specified VRF instance, use the vrf vrf-name
parameter. The vrf vrf-name parameter allows you to create a VPN routing or forwarding
instance specified by the vrf-name variable. The vrf-name variable specifies the name of the
VRF instance you want to create.
2. Enter the always-propagate command to enable a preferred BGP4 route (not installed in the
RTM) to be advertised to other BGP4 neighbors.
Brocade(config-bgp)#always-propagate
Syntax: always-propagate