Transporting Packets Across an IP Backbone with MPLS
As described in the previous section, PE 1 and PE 2 exchange routing information, including
MPLS labels for their customer sites, by means of a BGP session established between
them across the service provider core.
NOTE: To better understand MPLS before you read this section, see “Configuring MPLS”
on page 275.
Labels are employed in both the BGP control plane and the MPLS data plane. In the
control plane, BGP advertises a route with an in label; this in label is also the label needed
when MPLS traffic is received. BGP receives routes with an associated out label; the out
label is the label sent with MPLS traffic.
Consider the network shown in Figure 73 on page 394. If you display the in label on PE 1,
you see that MP-BGP advertises a labeled VPN-IPv4 prefix of 10.12.0.0/16 with an in label
of 24 (and an RD of 777:1, as shown in the illustration).
host1:pe1#show ip bgp vpn all field in-label
Prefix In-label
10.12.0.0/16 24
10.24.0.0/16 none
Figure 73: BGP/MPLS VPN Route Exchange
If you display the in label on PE 2, you see that MP-BGP advertises a labeled VPN-IPv4
prefix of 10.24.0.0/16 with an in label of 16 (and an RD of 777:5, as shown in the
illustration).
host2:pe2#show ip bgp vpn all field in-label
Prefix In-label
10.12.0.0/16 none
10.24.0.0/16 16
Copyright © 2010, Juniper Networks, Inc.394
JunosE 11.2.x BGP and MPLS Configuration Guide
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