Enabling Bgp Routing; Nonstop Forwarding Awareness - Cisco ME 3400 Software Configuration Manual

Configuring BGP

Nonstop Forwarding Awareness

The BGP NSF Awareness feature is supported for IPv4 in the metro IP access 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 the BGP Nonstop Forwarding (NSF) Awareness Feature Guide at this URL:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a008015fede.
html

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.
Beginning in privileged EXEC mode, follow these steps to enable BGP routing, establish a BGP routing
process, and specify a neighbor:
Command
Step 1
configure terminal
Step 2
ip routing
Step 3 router bgp autonomous-system
Step 4 network network-number [mask network-mask]
[route-map route-map-name]
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
35-46
Chapter 35
Purpose
Enter global configuration mode.
Enable IP routing (required only if IP routing is disabled).
Enable a BGP routing process, assign it an AS number, and
enter router configuration mode. The AS number can be from
1 to 65535, with 64512 to 65535 designated as private
autonomous numbers.
Configure a network as local to this AS, and enter it in the BGP
table.
Configuring IP Unicast Routing
OL-9639-07