Figure 53: Lsp Creation, Downstream-On-Demand, Ordered Control - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - BGP AND MPLS CONFIGURATION GUIDE 2010-10-12 Configuration Manual
Software for e series broadband services routers bgp and mpls configuration guide
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JunosE 11.3.x BGP and MPLS Configuration Guide
Figure 53: LSP Creation, Downstream-on-Demand, Ordered Control
228
In Figure 53 on page 228, LSR A sends a label request to LSR C. Before LSR C responds, it
sends its own request to LSR D. LSR D in turn makes a request for a label to LSR F. When
LSR F returns an acceptable label to LSR D, that label is for use only between LSRs D
and F. LSR D sends a label back to LSR C that this pair of LSRs will use. Finally, LSR C
sends back to LSR A the label that they will use. This completes the establishment of
the LSP.
Downstream-unsolicited means that MPLS devices do not wait for a request from an
upstream device before signaling FEC-to-label bindings. As soon as the LSR learns a
route, it sends a binding for that route to all peer LSRs, both upstream and downstream.
Downstream-unsolicited does not conserve labels, because an LSR receives label
mappings from neighbors that might not be the next hop for the destination; it is used
by BGP or LDP when adjacent peers are configured to use the platform label space.
Independent control means that the LSR sending the label acts independently of its
downstream peer. It does not wait for a label from the downstream LSR before it sends
a label to its peers. When an LSR advertises a label to an upstream neighbor before it
has received a label for the FEC from the next-hop neighbor, the LSP is terminated at
the LSR. Traffic for the destination cannot be label-switched all the way to the egress
LSR. If no inner label is present, then the traffic is routed instead of switched.
In Figure 54 on page 229, LSR D learns a route to some prefix. LSR D immediately maps a
label for this destination and sends the label to its peers, LSR B, LSR C, LSR E, and LSR
F. In the topology-driven network, the LSPs are created automatically with each peer
LSR.
Copyright © 2010, Juniper Networks, Inc.
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