Cisco 7609 User Manual

20-4
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
78-14064-04
Chapter 20 Configuring IPX Unicast Layer 3 Switching on Supervisor Engine 1
Understanding How IPX MLS Works
Received IPX packets are formatted (conceptually) as follows:
The PFC rewrites the Layer 2 frame header, changing the destination MAC address to the MAC address
of Host B and the source MAC address to the MAC address of the MSFC (these MAC addresses are
stored in the IPX MLS cache entry for this flow). The Layer 3 IPX addresses remain the same. The PFC
rewrites the switched Layer 3 packets so that they appear to have been routed by a router.
The PFC forwards the rewritten packet to Host B’s VLAN (the destination VLAN is saved in the IPX
MLS cache entry) and Host B receives the packet.
After the switch rewrites an IPX packet, it is formatted (conceptually) as follows:
IPX MLS Operation
Figure 20-1 displays a conceptual IPX MLS network topology. In this example, Host A is on the Sales
VLAN (IPX address 01.Aa), Host B is on the Marketing VLAN (IPX address 03.Bb), and Host C is on
the Engineering VLAN (IPX address 02.Cc).
When Host A initiates a file transfer to Host C, an IPX MLS entry for this flow is created (this entry is
the second item in the table shown in Figure 20-1). The PFC stores the MAC addresses of the MSFC and
Host C in the IPX MLS entry when the MSFC forwards the first packet from Host A through the switch
to Host C. The PFC uses this information to rewrite subsequent packets from Station A to Station C.
Similarly, a separate IPX MLS entry is created in the MLS cache for the traffic from Host A to Host B,
and for the traffic from Host B to Host A. The destination VLAN is stored as part of each IPX MLS entry
so that the correct VLAN identifier is used when encapsulating traffic on trunk links.
Layer 2 Frame Header Layer 3 IPX Header Data FCS
Destination Source Checksum/
IPX Length/
Transport Control
Destination Net/
Node/
Socket
Source Net/
Node/
Socket
MSFC MAC Source A MAC n Destination B IPX Source A IPX
Layer 2 Frame Header Layer 3 IPX Header Data FCS
Destination Source Checksum/
IPX Length/
Transport Control
Destination Net/
Node/
Socket
Source Net/
Node/
Socket
Destination B
MAC
MSFC MAC n+1 Destination B IPX Source A IPX

Cisco 7609 Specifications

General

Brand	Cisco
Model	7609
Category	Network Router
Language	English