Specifications

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Cisco IGX 8400 Series Provisioning Guide, Release 9.3.3 and Later Releases
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Chapter 10 Cisco IGX 8400 Series IP Service
IP Service Provisioning
Figure 10-18 shows the MPLS label swapping process. This process might take place during the
transportation of the IP packets, in the form of ATM cells across the network on the LVC1 and LVC2
virtual circuits:
1. An unlabeled IP packet with destination 204.133.44.129 arrives at edge label switching router
(LSR-A).
2. Edge LSR-A checks its label forwarding information base (LFIB) and matches the destination with
prefix 204.133.44.0/8.
3. Edge LSR-A converts the AAL5 frame to cells and sends the frame out as a sequence of cells on
1/VCI 50.
4. ATM-LSR-1 (a Cisco IGX 8410, 8420, or 8430 label switch router), controlled by a routing engine,
performs a normal switching operation by checking its LFIB and switching incoming cells on
interface 2/VCI 50 to outgoing interface 0/VCI 42.
5. ATM-LSR-2 checks its LFIB and switches incoming cells on interface 2/VCI 42 to outgoing
interface 0/VCI 90.
6. Edge LSR-C receives the incoming cells on incoming interface 1/VCI 90, checks its LFIB, converts
the ATM cells back to an AAL5 frame, and an IP packet, and then sends the outgoing packet to its
LAN destination 204.133.44.129.