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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 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 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.
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
Optional BGP4 configuration tasks
Brocade FastIron Layer 3 Routing Configuration Guide
53-1003903-04
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Содержание ICX 7250 series
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