Brocade Communications Systems Layer 3 Routing Configuration ICX 6650 - Manual (Page 331)

Brocade ICX 6650 Layer 3 Routing Configuration Guide 313
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Optional BGP4 configuration tasks
The next-hop IP address for 192.0.0.1 is not an IGP route, which means the BGP route destination
still cannot be reached through IP. The recursive next-hop lookup feature performs a lookup on
10.0.0.1 next-hop gateway.
This lookup results in an IGP route. In fact, this route is a directly-connected route. As a result, the
BGP route destination is now reachable through IGP, which means the BGP route is eligible for
installation in the IP route table. Here is the BGP route in the IP route table.
This Layer 3 switch can use this route because the Layer 3 switch has an IP route to the next-hop
gateway. Without recursive next-hop lookups, this route would not be in the IP route table.
Enabling recursive next-hop lookups
The recursive next-hop lookups feature is disabled by default. To enable recursive next-hop
lookups, enter the next-hop-recursion command at the BGP configuration level of the CLI.
Brocade(config-bgp-router)#next-hop-recursion
Syntax: [no] next-hop-recursion
Changing administrative distances
BGP4 routers can learn about networks from various protocols, including the EBGP portion of BGP4
and IGPs such as OSPF and RIP. Consequently, the routes to a network may differ depending on the
protocol from which the routes were learned.
To select one route over another based on the source of the route information, the Layer 3 switch
can use the administrative distances assigned to the sources. The administrative distance is a
protocol-independent metric that IP routers use to compare routes from different sources.
The Layer 3 switch re-advertises a learned best BGP4 route to the Layer 3 switch neighbors even
when the software does not also select that route for installation in the IP route table. The best
BGP4 routes is the BGP4 path that the software selects based on comparison of the paths’ BGP4
route parameters. Refer to
“How BGP4 selects a path for a route” on page 283.
Brocade#show ip bgp route 192.168.0.0
Number of BGP Routes matching display condition : 1
Status A:AGGREGATE B:BEST b:NOT-INSTALLED-BEST C:CONFED_EBGP D:DAMPED
H:HISTORY I:IBGP L:LOCAL M:MULTIPATH S:SUPPRESSED
Prefix Next Hop Metric LocPrf Weight Status
1 192.168.0.0/24 10.0.0.1 1 100 0 BI
AS_PATH: 65001 4355 1
Brocade#show ip route 10.0.0.1
Total number of IP routes: 38
Network Address NetMask Gateway Port Cost Type
10.0.0.0 255.255.255.0 0.0.0.0 1/1/1 1 D
AS_PATH: 65001 4355 1
Brocade#show ip route 192.168.0.0/24
Total number of IP routes: 38
Network Address NetMask Gateway Port Cost Type
192.168.0.0 255.255.255.0 10.0.0.1 1/1/1 1 B
AS_PATH: 65001 4355 1