Cisco Systems EA6500 Manual De Usuario
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Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E
78-14099-04
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.
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.
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
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).
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
the second item in the table shown in
). 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.
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.
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