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NHRP in a Pure LAN Emulation Environment
In the LAN emulation case, routers use the IBM extensions to provide NBMA
information for devices on their ELANs. When Device1 receives traffic from host A
destined to host B, it originates a Next Hop Resolution Request and sends it on the
routed path. Device2 replies to the request with NBMA information about host B,
one of the stations that it serves because they are on the same ELAN. Device1
then can establish a data direct VCC to host B even though host B does not
participate in or support the NHRP exchanges. Note that this VCC would be used
only for traffic in the direction from A to B. Similarly when host B sends traffic to
host A, Device2 generates a Next Hop Resolution Request, Device1 replies with
addressing information about host A, and Device2 establishes a data direct VCC to
A for traffic from B to A.
The LECs in this example are standard-compliant devices with no NHRP support.
They must satisfy the LEC requirements described in “NHRP Implementation” on
page 352 ).
Nothing special has to be configured in these devices or in the NHRP servers. The
NHRP traffic flows over the ELAN subnet with no additional VCs.
NHRP in a LAN Emulation Environment with LAN Switches
In this example, the source and destination stations are attached to legacy LANs
and do not connect to the ATM net work. LAN switches operating as LAN Emulation
Clients give ATM connectivity to the legacy LAN devices. The enhancements to
NHRP and the IBM extensions allow the same kind of “one-hop routing” in this
environment as described in the previous example. With the enhancements, the
servers exchange the actual MAC addresses and routing information for the
legacy-LAN devices. The 2210s can then establish data direct VCCs with the
switches and pass the traffic directly. There is only one router “hop” in the path,
although the traffic passes through two LAN switches.
Figure 30. NHRP in an ELAN Environment
Using NHRP
Chapter 11. Using NHRP 349