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Catalyst 6000 Family Software Configuration Guide—Releases 6.3 and 6.4
78-13315-02
Chapter 14 Configuring MLS
Understanding How Layer 3 Switching Works
Figure 14-1 IP MLS Example Topology
Figure 14-2
shows a simple 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 B, an IPX MLS entry for this flow is created (this entry is
the first item in the table shown in
Figure 14-1
). The PFC stores the MAC addresses of the MSFC and
Host B in the IPX MLS entry when the MSFC forwards the first packet from Host A through the switch
to Host B. The PFC uses this information to rewrite subsequent packets from Host A to Host B.
Similarly, a separate IPX MLS entry is created in the MLS cache for the traffic from Host A to Host C,
and for the traffic from Host C 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.
Source IP
Address
171.59.1.2
171.59.1.2
Host A
171.59.1.2
Host B
171.59.3.1
Host C
171.59.2.2
171.59.2.2
171.59.1.2: 2000
Data
171.59.3.1
171.59.2.2
171.59.1.2
FTP
HTTP
HTTP
Dd:Bb
Dd:Cc
Dd:Aa
Marketing
Engineering
Sales
Destination
IP Address
Application
Rewrite Src/Dst
MAC Address
Destination
VLAN
MSFC
Subnet 1/Sales
MAC = Aa
MAC = Dd
MAC = Bb
MAC = Cc
Subnet 3/Marketing
Subnet 2/Engineering
Aa:Dd
171.59.1.2: 2000
Data
Dd:Cc
25481
