When you congure maxas-limit in , the behavior of the device changes to rst check the length of the AS paths in the UPDATE
messages and then to apply the inbound policy. If the AS path exceeds the congured 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• Processes the withdrawn NLRIs in the same update message
If a route from a peer exceeds the congured Maximum AS path limit, the device also removes the same route from that peer, if it exists,
from its own RIB.
After a maximum AS path length is congured, the maximum AS path limit applies to all new inbound routes. To update previously
stored routes, you must perform an inbound soft reset for all of the address families activated for that particular BGP neighbor session.
NOTE
If the neighbor soft-reconguration feature is enabled, you must perform a hard reset on the device to impose the maximum
length limit.
NOTE
maxas-limit in is checked against the received AS_PATH and AS4_PATH attributes.
BGP devices check for and, if congured, apply maxas-limit in in the following order:
1. Neighbor value
2. Peer group value
3. Global value
In a case where a neighbor has no maximum AS limit, a peer group has a value of 3 congured, and the system has a value of
9 congured, all of the devices in the peer group will only use the peer group value; the global value will never be used.
Setting a global maximum AS path limit
The syntax for the global maximum AS path limit command is:
Syntax: [no] maxas-limit in num
The maxas-limit keyword species the limit on the AS numbers in the as-path attribute. The in keyword allows the as-path attribute from
any neighbor imposing a limit on AS numbers received. The default maximum length for the global system is 300. The range is 0 - 300.
The no keyword removes the conguration at the global level.
NOTE
The device applies the BGP4 maximum AS path limit on a per virtual device basis.
To congure the global Maximum AS path limit to 15, enter the following command:
device(config-bgp)# maxas-limit in 15
Setting a maximum AS path limit for a peer group or neighbor
To set maximum AS path limit for a peer group or a neighbor, the syntax is:
Syntax: neighbor { ip-addr | peer-group-name } maxas-limit in [ num | disable ]
Specifying a maximum AS path length
FastIron Ethernet Switch Layer 3 Routing
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