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Routing Engine So
ftware Components
• SNMP and MIB II Processes o n page 26
• Management Process on page 27
• Routing Engine
Kernel on page 27
Routing Protoc
ol Process
The JUNOS software routing protocol process controls the routing protocols that run on the
router. The ro
uting protocol process starts all configured routing protocols and handles all
routing messages. It consolidates the routing information learned from all routing protocols
into common routing tables. From this routing information, the routing protocol process
determines th
e active routes to network destinations and installs these routes into the
Routing Engine’s forwarding table. Finally, the routing protocol process implements the
routing policies you specify, which determine how routing information is transferred between
the routing p
rotocols and the routing table .
This section discusses the following topics:
• IPv4 Routing Protocols on page 22
• IPv6 Routing Protocols on page 24
• Routing and Forwarding Tables on page 24
• Routing Polic
y on page 25
For complete information about routing concepts, see the JUNO S Internet sof tware
configurati
on guides.
IPv4 Routing Protocols
The JUNOS Internet software implements full I P routing functionality, providing support for
IP version 4 (IPv4). The routing protocols are fully interoperable with existing IP routing
protocols and provide the scale and control necessary for the Internet core. The software
provides support for the following routing and traffic engineering protocols:
• Unicast routing protocols
• BGP—Border Gateway Protocol, version 4, is an Exterior Gateway Protocol (EGP)
that guarantees loop-free exchange of routing information between routing
domains (also called autonomous systems). BGP, in conjunction with JUNOS
routing policy, provides a system of administrative checks and balances that can
be used to implement peering and transit agreements.
• ICMP—Internet C ontrol Message Protocol router discovery is a method that
hosts can use to discover the addresses o f operational routers on a subnet.
• IS-IS—Intermediate System-to-Intermediate System is a link-state interior
gateway protocol (IGP) for IP networks that uses the shortest-path-first algorithm
(SPF algorithm, also called t he Dijkstra algorithm) to determine routes.
22 M5 and M10 Internet Routers Hardware Guide