Enabling recursive next-hop lookups, Example when recursive route lookups are disabled, Example when recursive route lookups are enabled – Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide User Manual

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Enabling recursive next-hop lookups

The recursive next-hop lookups feature is disabled by default. To enable recursive next-hop lookups,
enter the following command at the BGP4 configuration level of the CLI.

device(config-bgp-router)# next-hop-recursion

Syntax: [no] next-hop-recursion

Example when recursive route lookups are disabled

The output here shows the results of an unsuccessful next-hop lookup for a BGP4 route. In this case,
next-hop recursive lookups are disabled. This example is for the BGP4 route to network 10.0.0.0/24.

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 Next Hop MED LocPrf Weight Status

1 0.0.0.0/0 10.1.0.2 0 100 0 BI

AS_PATH: 65001 4355 701 80

2 10.10.0.0/24 10.0.0.1 1 100 0 BI

AS_PATH: 65001 4355 1

3 10.40.0.0/24 10.1.0.2 0 100 0 BI

AS_PATH: 65001 4355 701 1 189

4 10.0.0.0/24 10.0.0.1 1 100 0 I

AS_PATH: 65001 4355 3356 7170 1455

5 10.25.0.0/24 10.157.24.1 1 100 0 I

AS_PATH: 65001 4355 701

In this example, the device cannot reach 10.0.0.0/24, because the next-hop IP address for the route is
an IBGP route instead of an IGP route, and is considered unreachable by the device. The IP route
table entry for the next-hop gateway for the BGP4 route’s next-hop gateway (10.0.0.1/24) is shown
here.

device#show ip route 10.0.0.1

Total number of IP routes: 37

Network Address NetMask Gateway Port Cost Type

10.0.0.0 10.255.255.255 10.0.0.1 1/1 1 B

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 NetMask Gateway Port Cost Type

0.0.0.0 0.0.0.0 10.0.0.202 1/1 1 S

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.