Brocade FastIron Ethernet Switch Layer 3 Routing Configura Manual de usuario descargar pdf (Pagina 420)

When selecting a route from among different sources (BGP4, OSPF, RIP, static routes, and so on),

the software compares the routes on the basis of the administrative distance for each route. If the

administrative distance of the paths is lower than the administrative distance of paths from other

sources (such as static IP routes, RIP, or OSPF), the BGP4 paths are installed in the IP route table.

The default administrative distances on the device are:

• Directly connected - 0 (this value is not configurable)

• Static - 1 is the default and applies to all static routes, including default routes. This can be assigned

a different value.

• EBGP - 20

• OSPF - 110

• RIP - 120

• IBGP - 200

• Local BGP4 - 200

• Unknown - 255 (the device will not use this route)

Lower administrative distances are preferred over higher distances. For example, if the device

receives routes for the same network from OSPF and from RIP, the device will prefer the OSPF route

by default. The administrative distances are configured in different places in the software. The device

re-advertises a learned best BGP4 route to neighbors by default, regardless of whether the

administrative distance for the route is lower than the administrative distances of other routes from

different route sources to the same destination:

• To change the EBGP, IBGP, and Local BGP4 default administrative distances, refer to the

instructions in this section.

• To change the default administrative distance for OSPF, RIP, refer to Configuring a static BGP4

network on page 472.

• To change the administrative distance for static routes, refer to the instructions in this section.

To change the default administrative distances for EBGP, IBGP, and Local BGP4, enter a command

such as the following.

device(config-/jointfilesconvert/1441084/bgp-router)# distance 200 200 200

Syntax: [no] distance external-distance internal-distance local-distance

The external-distance sets the EBGP distance and can be a value from 1 through 255.

The internal-distance sets the IBGP distance and can be a value from 1 through 255.

The local-distance sets the Local BGP4 distance and can be a value from 1 through 255.

Requiring the first AS to be the neighbor AS

By default, the Brocade device does not require the first AS listed in the AS_SEQUENCE field of an

AS path update message from EBGP neighbors to be the AS of the neighbor that sent the update.

However, you can enable the Brocade device to have this requirement. You can enable this

requirement globally for the device, or for a specific neighbor or peer group. This section describes

how to enable this requirement.

When you configure the device to require that the AS an EBGP neighbor is in be the same as the first

AS in the AS_SEQUENCE field of an update from the neighbor, the device accepts the update only if

the AS numbers match. If the AS numbers do not match, the Brocade device sends a notification

message to the neighbor and closes the session. The requirement applies to all updates received from

EBGP neighbors.

The hierarchy for enforcement of this feature is: a neighbor will try to use the enforce-first-as value if

one is configured; if none is configured, the neighbor will try to use the configured value for a peer

Requiring the first AS to be the neighbor AS

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