Router Ids; Autonomous Systems - Cisco Nexus 3000 Series Configuration Manual

Chapter 1 Overview
S e n d d o c u m e n t c o m m e n t s t o n e x u s 3 k - d o c f e e d b a c k @ c i s c o . c o m

Router IDs

Each routing process has an associated
system. If you do not configure the router ID, Cisco NX-OS selects the router ID based on the following
criteria:
•
•
•

Autonomous Systems

An
Autonomous systems divide global external networks into individual routing domains, where local
routing policies are applied. This organization simplifies routing domain administration and simplifies
consistent policy configuration.
Each autonomous system can support multiple interior routing protocols that dynamically exchange
routing information through route redistribution. The Regional Internet Registries assign a unique
number to each public autonomous system that directly connects to the Internet. This autonomous
system number (AS number) identifies both the routing process and the autonomous system.
Cisco NX-OS supports 4-byte AS numbers.
Table 1-1
2-Byte Numbers
1 to 64511
64512 to 65534 0.64512 to 0.65534 64512 to 65534
65535
N/A
1. RIR=Regional Internet Registries
Private autonomous system numbers are used for internal routing domains but must be translated by the
router for traffic that is routed out to the Internet. You should not configure routing protocols to advertise
private autonomous system numbers to external networks. By default, Cisco NX-OS does not remove
private autonomous system numbers from routing updates.
Cisco NX-OS prefers loopback0 over any other interface. If loopback0 does not exist, then Cisco
NX-OS prefers the first loopback interface over any other interface type.
If you have not configured no loopback interfaces, Cisco NX-OS uses the first interface in the
configuration file as the router ID. If you configure any loopback interface after Cisco NX-OS
selects the router ID, the loopback interface becomes the router ID. If the loopback interface is not
loopback0 and you configure loopback0 later with an IP address, the router ID changes to the IP
address of loopback0.
If the interface that the router ID is based on changes, that new IP address becomes the router ID. If
any other interface changes its IP address, there is no router ID change.
(AS) is a network controlled by a single technical administration entity.
autonomous system
AS Numbers
4-Byte Numbers in
AS.dot Notation
0.1 to 0.64511
0.65535
1.0 to 65535.65535 65536 to
Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, NX-OS Release 5.0(3)U1(1)
ID. You can configure the router ID to any interface in the
router
Table 1-1 lists the AS number ranges.
4-Byte Numbers in
plaintext Notation Purpose
1 to 64511 Public AS (assigned by RIR)
Private AS (assigned by local
administrator)
65535 Reserved
Public AS (assigned by RIR)
4294967295
Information About Layer 3 Unicast Routing
1
1-5