Local route
The first routing entry in the IP host node routing table is called the Local Route and
is often generated automatically after the node’s interface is configured with an IP
address and a subnet mask. This IP Prefix is simply the subnet address (IP address
with subnet mask) of the locally attached subnet. This entry says that every packet
generated with destination address of the local subnet will be sent out on the local
LAN. There is no “Next Hop Node”. Instead <Local Subnet> is simply a flag which
says to take the destination IP address from the IP packet and resolve it directly on the
local LAN. Notice this routing entry would be essential in nodes I4 and I5 if they
wished to communicate with each other. There is one Local Route entry for each
interface. These IP Hosts only have a single interface and so only a single Local Route
entry.
Default route
The second routing entry in the IP host node routing table is the IP Prefix 0.0.0.0 / 0,
which is called the Default Route. This prefix will match every destination IP address
and so in effect, this routing entry says that every packet generated will be sent to the
specified next hop. In all cases, the specified next hop is the DSwT node which is
identified by its IP address. Notice that routes for the local subnet also match the
Default Route. Of course this is not the intention so there is another essential rule for
all routing tables, which says that match with the longest prefix route must be selected.
This is fundamental to IP Routing Tables and must be followed in all cases.
Routing table for external routers
For external routers there are two possible hop ports (LAN 1 and LAN 2). The <Local
subnet> routes can be added automatically when the router interfaces are configured
(assigned IP address and subnet mask).
The routing tables for routers C1 and C2, see the previous figure:
External
Routers
Final Destination Next Hop
Port Node
C1 120.2.1.0 / 24
120.1.1.0 / 24
120.1.0.0 / 16
120.3.0.0 / 16
LAN 1
LAN 2
LAN 2
LAN 2
<Local Subnet>
<Local Subnet>
120.1.1.2
120.1.1.2
C2 120.3.4.0 / 24
120.1.4.0 / 24
120.1.0.0 / 16
120.2.0.0 / 16
LAN 1
LAN 2
LAN 2
LAN 2
<Local Subnet>
<Local Subnet>
120.1.4.3
120.1.4.3
Management communication setup
Example of dual stack with tunneling
....................................................................................................................................................................................................................................
4-24
Alcatel-Lucent - Proprietary
See notice on first page
365-312-807R7.2
Issue 4, May 2007
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