Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 469)

NOTE
Traffic loss on a BGP4 route occurs when a device is advertising preferred BGP4 routes not installed in
the RTM as part of the forwarding path.
Because the BGP4 route 10.12.0.0/24 is not considered as the best BGP4 route, the route is not
advertised to other BGP4 neighbors.
device(config-bgp)# show ip bgp route 10.12.0.0/24
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 Next Hop MED LocPrf Weight Status
1 10.12.0.0/24 10.100.100.4 100 0 E
AS_PATH: 48 1994 65148 21948 6461 1239 4837 4808 17431 18245
Last update to IP routing table: 0h16m2s
No path is selected as BEST route
Syntax: show ip bgp route ip-address/prefix
After enabling the always-propagate command, the BGP4 route is now considered the best BGP4
route, even though the route is not installed in the RTM. Because the rib-route-limit command was
configured to allow for only 300,000 routes in the RTM some preferred BGP4 routes are not installed in
the RTM, and are not advertised to other BGP4 neighbors. By enabling the always-propagate
command, the device is now able to advertise those preferred BGP4 routes to other BGP4 neighbors. In
the following example, the Status field displays "bE" indicating that the route is now considered the best
BGP4 route for forwarding and will be advertised to other BGP4 neighbors.
device(config-bgp)# show ip bgp route 10.12.0.0/24
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 Next Hop MED LocPrf Weight Status
1 10.12.0.0/24 10.100.100.4 100 0 bE
AS_PATH: 48 1994 65148 21948 6461 1239 4837 4808 17431 18245
Last update to IP routing table: 0h12m53s
Route is to be sent to 1 peers:
10.0.0.14(6)
For an explanation of the fields displayed in the output of the show ip bgp route command, refer to
Displaying information for a specific route on page 497.
Specifying a maximum AS path length
You can use the maxas-limit in command to configure a device running BGP4 to discard routes that
exceed a specified AS path limit. This limit can be configured globally, for peer groups, and for BGP
neighbors.
When you configure maxas-limit in , the behavior of the device changes to first check the length of the
AS paths in the UPDATE messages and then to apply the inbound policy. If the AS path exceeds the
configured length, then the device performs the following actions:
• Does not store the route in the RIB and does not forward the NLRIs and attributes contained in the
UPDATE message for that route
• Logs an error
• Processes the withdrawn NLRIs in the same update message
Specifying a maximum AS path length
FastIron Ethernet Switch Layer 3 Routing Configuration Guide 469
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