Reference Guide

Layer 3
Border Gateway
Protocol (BGP)
Provides an external gateway protocol that transmits inter-domain routing information within and between
autonomous systems (see BGP Commands).
Equal Cost Multi-
Path (ECMP)
Provides next-hop packet forwarding to a single destination over multiple best paths (see ECMP Commands).
IPv4 Routing Provides forwarding of packets to a destination IP address, based on a routing table. This routing table denes how
packets are routed — dynamically, broadcasted directly to, using proxy ARP, as well as what type of information is
included with the packets (see IPv4 Routing Commands).
IPv6 Routing Provides routing for the IPv6 address space, stateless auto-conguration, header format simplications, and
improved support for options and extensions (see IPv6 Routing Commands).
Open Shortest Path
First (OSPF)
Provides a link-state routing protocol that communicates with all other devices in the same autonomous system
area using link-state advertisements (LSAs). OS10 supports up to 10,000 OSPF routes for OSPFv2 to designate up
to 8,000 routes as external, and up to 2,000 as inter/intra area routes (see OSPF Commands).
Virtual Router
Redundancy
Protocol (VRRP)
Provides a mechanism to eliminate a single point of failure in a statically routed network (see VRRP Commands).
Border gateway protocol
Border gateway protocol (BGP) is an interautonomous system routing protocol that transmits interdomain routing information within and
between autonomous systems (AS). The primary function of BGP is to exchange network reachability information with other BGP systems.
BGP adds reliability to network connections by using multiple paths from one router to another. Unlike most routing protocols, BGP uses
TCP as its transport protocol.
Autonomous systems
BGP autonomous systems are a collection of nodes under a single administration with shared network routing policies. Each AS has a
number, which an Internet authority assigns—you do not assign the BGP number.
The Internet Assigned Numbers Authority (IANA) identies each network with a unique AS number (ASN). The AS numbers 64512 through
65534 are reserved for private purposes. The AS numbers 0 and 65535 cannot be used in a live environment. IANA assigns valid AS
numbers in the range of 1 to 64511.
Multihomed AS
Maintains connections to more than one other AS. This group allows the AS to remain connected to the Internet if
a complete failure occurs to one of their connections. This type of AS does not allow trac from one AS to pass
through on its way to another AS.
Stub AS Connected to only one AS.
Transit AS Provides connections through itself to separate networks. For example, Router 1 uses Router 2—the transit AS, to
connect to Router 4. Internet service providers (ISPs) are always a transit AS because they provide connections
from one network to another. An ISP uses a transit AS to sell transit service to a customer network.
When BGP operates inside an AS - AS1 or AS2, it functions as an internal border gateway protocol (IBGP). When BGP operates between
AS endpoints - AS1 and AS2, it functions as an external border gateway protocol (EBGP). IBGP provides routers inside the AS with the
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