Brocade Communications Systems FastIron SX 800 Configuration Manual page 384

Optional BGP4 configuration tasks
Since the route to the next-hop gateway is a BGP4 route, and not an IGP route, it cannot be used to reach 10.0.0.0/24. In this case, the
device tries to use the default route, if present, to reach the subnet that contains the BGP4 route next-hop gateway.
device# show ip route 10.0.0.0/24
Total number of IP routes: 37
Network Address
0.0.0.0
Example when recursive route lookups are enabled
When recursive next-hop lookups are enabled, the device continues to look up the next-hop gateways along the route until the device
finds an IGP route to the BGP4 route destination.
device# show ip bgp route
Total number of BGP Routes: 5
Status A:AGGREGATE B:BEST b:NOT-INSTALLED-BEST C:CONFED_EBGP D:DAMPED
E:EBGP H:HISTORY I:IBGP L:LOCAL M:MULTIPATH m:NOT-INSTALLED-MULTIPATH
S:SUPPRESSED F:FILTERED s:STALE
Prefix
1 0.0.0.0/0
AS_PATH: 65001 4355 701 80
2 10.10.0.0/24
AS_PATH: 65001 4355 1
3 10.40.0.0/24
AS_PATH: 65001 4355 701 1 189
4 10.0.0.0/24
AS_PATH: 65001 4355 3356 7170 1455
5 10.25.0.0/24
AS_PATH: 65001 4355 701
The first lookup results in an IBGP route, to network 10.0.0.0/24.
device# show ip route 10.0.0.1
Total number of IP routes: 38
Network Address
10.0.0.0
AS_PATH: 65001 4355 1
Since the route to 10.0.0.1/24 is not an IGP route, the device cannot reach the next hop through IP, and so cannot use the BGP4 route.
In this case, since recursive next-hop lookups are enabled, the device next performs a lookup for the next-hop gateway to 10.0.0.1's
next-hop gateway, 10.0.0.1.
device# show ip bgp route 10.0.0.0
Number of BGP Routes matching display condition : 1
Status A:AGGREGATE B:BEST b:NOT-INSTALLED-BEST C:CONFED_EBGP D:DAMPED
E:EBGP H:HISTORY I:IBGP L:LOCAL M:MULTIPATH m:NOT-INSTALLED-MULTIPATH
S:SUPPRESSED F:FILTERED s:STALE
Prefix
1 10.0.0.0/24
AS_PATH: 65001 4355 1
The next-hop IP address for 10.0.0.1 is not an IGP route, which means the BGP4 route destination still cannot be reached through IP.
The recursive next-hop lookup feature performs a lookup on the next-hop gateway for 10.0.0.1
device# show ip route 10.0.0.1
Total number of IP routes: 38
Network Address
10.0.0.0
AS_PATH: 65001 4355 1 1
384
NetMask Gateway
0.0.0.0 10.0.0.202
Next Hop MED
10.1.0.2 0
10.0.0.1 1
10.1.0.2 0
10.0.0.1 1
10.157.24.1 1
NetMask Gateway
255.255.255.0 10.0.0.1
Next Hop Metric
10.0.0.1 1
NetMask Gateway
255.255.255.0 0.0.0.0
Port Cost Type
1/1 1 S
LocPrf Weight Status
100 0
100 0
100 0
100 0 BI
100 0
Port Cost Type
1/1 1 B
LocPrf Weight Status
100 0 BI
Port Cost Type
1/1 1 D
BI
BI
BI
I
FastIron Ethernet Switch Layer 3 Routing
53-1003627-04