Specifications

Page 105 /148
selected manually by network operators or automatically by constraint-based
routing software.
Note that multiple paths can be configured for a particular LSP. If a path is
designated as the primary path, then it will be used first to establish the LSP. If
the primary path fails then a secondary path is chosen. If the primary path
subsequently becomes available then the LSP is moved from the secondary to
the primary.
JUNOS has a rich set of MPLS features which will continue to get enhanced.
Some of the other main features are:
§ BGP shortcuts
§ GP (IS-IS/OSPF) shortcuts
§ Standby Secondary Paths
§ Fast re-route
§ Record-Route
§ Admin Groups (Affinity bits)
§ Adaptive LSPs
§ LSP Priority and Preemption
§ LSP Re-optimization
§ MPLS Class of Service
§ CSPF Load Balancing
§ MPLS TTL Decrement On/Off
§ RSVP Refresh
§ Circuit Cross Connect
o Layer-2 Switching
o LSP Tunneling
o LSP Stitching
§ Tunneling LDP LSPs in RSVP LSPs
More specific details about the MPLS implementation can be found in the JUNOS
manual at :
http://www.juniper.net/techpubs/software/junos41/swconfig-traffic-
eng41/download/swconfig-traffic-eng41.pdf
Also more information about MPLS and RSVP can be found in the following
Juniper white papers:
§ MPLS : Enhancing Routing in the New Public Network
http://www.juniper.net/techcenter/techpapers/200001.html
§ Traffic Engineering for the New Public Network
http://www.juniper.net/techcenter/techpapers/200004.html
§ RSVP Signaling Extensions for MPLS Traffic Engineering
http://www.juniper.net/techcenter/techpapers/200006.html
3.3.1 LDP
In addition to RSVP, Junos also supports the IETF’s Label Distribution Protocol
(LDP). A fundamental concept in MPLS is that two Label Switching Routers
(LSRs) must agree on the meaning of the labels used to forward traffic between
them. LDP supports the general components of the Internet Draft draft-ietf-mpls-
ldp-05.txt along with these optional features listed in the draft specification:
§ Upstream unsolicited label distribution discipline
§ Liberal label retention mode.
§ Neighbor discovery.
There are two primary reasons for supporting LDP. The first is to interoperate
with access devices that support VPNs and use LDP to signal LSPs for tunneling
the VPN traffic between each router; in this situation the access devices would be
from any vendor and the core would be Juniper. The second is to support a core
IP network that does not carry full Internet routes (i.e., the edge routers have full