Alcatel-Lucent 1643 AMS User's Operation Manual page 111

Management communication setup
Final destination
This column of the Routing Table is a list of all the final destination nodes. When a
packet is received at this node, then the destination address in that packet is checked
against the list of destinations in the destination column of the routing table. If there is
no entry in the table for the packet destination, then the node will not know how to
route the packet and will execute the error procedure (which involves discarding the
packet and trying to send an error message packet back to the source). If a match is
found, the next hop towards the destination can be looked up in the "Next Hop"
column.
IP prefixes
An IP Prefix is a mechanism of identifying a collection of IP addresses with some
common root. The general principle is to choose a mask which identifies a suitable
first part of the IP address which summarizes a number of addresses. For example, the
addresses 120.10.2.1, 120.10.2.5 and 120.10.2.13 can be summarized by the IP Prefix:
120.10.2.0 / 24. The 24 identifies the first 24 bits of the address. Summarizing IP
addresses is a very powerful way to reduce the number of entries in a Routing Table.
Next hop
Two pieces of information are needed in order to identify the next hop node:
• on which subnetwork (for example on which exit port) is the next hop node,
• which node on that subnetwork is the next hop.
This is shown in the figure below.
To send a packet to the destination Dest, the Source must identify the node Next Hop.
This is identified by the subnetwork (on Port 2 of Source) and then the node on that
subnetwork (identified by B). In OSI terminology the address B is known as a
Subnetwork Point of Attachment (SNPA), which is the point that the node is attached
to the subnetwork.
The second column in the Routing Table is the next hop and is divided into two parts:
• the Next Hop Subnetwork
• the Next Hop Node.
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365-312-807R7.2
Issue 4, May 2007
Alcatel-Lucent - Proprietary
See notice on first page
Dual stack with tunneling (DSwT)
4-21