Cisco IE 4000, Software Configuration Manual

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Configuring IP Unicast Routing
Configuring BGP
Nonstop Forwarding Awareness
The BGP NSF Awareness feature is supported for IPv4 in the IP services image. To enable this feature with BGP routing,
you need to enable Graceful Restart. When the neighboring router is NSF-capable, and this feature is enabled, the Layer
3 switch continues to forward packets from the neighboring router during the interval between the primary Route
Processor (RP) in a router failing and the backup RP taking over, or while the primary RP is manually reloaded for a
nondisruptive software upgrade. For more information, see
IP Routing: BGP Configuration Guide, Cisco IOS Release
15M&T .
Enabling BGP Routing
To enable BGP routing, you establish a BGP routing process and define the local network. Because BGP must completely
recognize the relationships with its neighbors, you must also specify a BGP neighbor.
BGP supports two kinds of neighbors: internal and external. Internal neighbors are in the same AS; external neighbors
are in different autonomous systems. External neighbors are usually adjacent to each other and share a subnet, but
internal neighbors can be anywhere in the same AS.
The switch supports the use of private AS numbers, usually assigned by service providers and given to systems whose
routes are not advertised to external neighbors. The private AS numbers are from 64512 to 65535. You can configure
external neighbors to remove private AS numbers from the AS path by using the
neighbor remove-private-as router
configuration command. Then when an update is passed to an external neighbor, if the AS path includes private AS
numbers, these numbers are dropped.
If your AS must pass traffic through it from another AS to a third AS, it is important to be consistent about the routes it
advertises. If BGP advertises a route before all routers in the network learn about the route through the IGP, the AS might
receive traffic that some routers can not yet route. To prevent this from happening, BGP must wait until the IGP has
propagated information across the AS so that BGP is
synchronized with the IGP. Synchronization is enabled by default.
If your AS does not pass traffic from one AS to another AS, or if all routers in your autonomous systems are running BGP,
you can disable synchronization, which allows your network to carry fewer routes in the IGP and allows BGP to converge
more quickly.
BEFORE YOU BEGIN
You should know your network design and how you want traffic to flow through it before configuring BGP. Gather the
network requirements you need, which should include the following:

Whether you need to run IBGP for internal connectivity

External connectivity to the service provider network

Configuration parameters such as neighbor IP addresses and their AS number, and which networks you will advertise
through BGP
Synchronization (BGP and IGP) Enabled.
Table map update Disabled.
Timers Keepalive: 60 seconds; holdtime: 180 seconds.
1. NSF = Nonstop Forwarding
2. BGP NSF Awareness can be enabled for IPv4 on switches with the IP services image by enabling Graceful Restart.
Feature Default Setting