The algorithms used to forward packets in IP networks are, for
example, documented in RFC 1812 and the various routing protocols that may be used
to populate the forwarding tables (such as OSPF and BGP) are documented in other
IETF RFCs.
422 Chapter 14
In a connection-orientated network, however, packets are forwarded along predefined
connections from the source to the destination. Forwarding is again based on running
an algorithm using the packet header and a forwarding database as inputs, but in this
case, the information encoded in the packet header is simply a connection identifier (or
???label???), which is generally assigned locally by the router and swapped to the identifier
assigned by the next hop router (i.e., the next router in the path toward the destination)
before forwarding to that router. The forwarding database consists simply of a list
of labels??”each associated with an egress interface and next hop router and, if labels
are locally assigned, the label assigned by that next hop router. Connections (in MPLS
these are called Label Switched Paths or LSPs) may be established either by manual
configuration or by using a signaling protocol.
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