Ip Mls Operation - Cisco 6500 Series Software Configuration Manual

Chapter 19 Configuring IP Unicast Layer 3 Switching on Supervisor Engine 1
After the PFC performs the packet rewrite, the packet is formatted (conceptually) as follows:
Frame Header
Destination
Host B MAC

IP MLS Operation

Figure 19-1
(IP subnet 171.59.1.0), Host B is on the Marketing VLAN (IP subnet 171.59.3.0), and Host C is on the
Engineering VLAN (IP subnet 171.59.2.0).
When Host A initiates an HTTP file transfer to Host C, an MLS entry for this flow is created (this entry
is the second item in the MLS cache shown in
MSFC and Host C in the 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 Host A to Host C.
Figure 19-1 IP MLS Example Topology
Source IP
Address
171.59.1.2
171.59.1.2
171.59.2.2
MAC = Aa
Host A
171.59.1.2
78-14099-04
Source
MSFC MAC
shows a simple IP MLS network topology. In this example, Host A is on the Sales VLAN
Destination
Application
IP Address
171.59.3.1
171.59.2.2
171.59.1.2
Subnet 1/Sales
Data 171.59.1.2: 2000 Aa:Dd
Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E
IP Header
Destination Source TTL Checksum
Host B IP Host A IP n-1
Figure 19-1). The PFC stores the MAC addresses of the
Rewrite Src/Dst
MAC Address
FTP Dd:Bb
HTTP Dd:Cc
HTTP Dd:Aa
MAC = Dd
MSFC
Data
Understanding How IP MLS Works
Payload
Data
calculation2
Destination
VLAN
Marketing
Engineering
Sales
MAC = Bb
Host B
171.59.3.1
MAC = Cc
Host C
171.59.2.2
171.59.1.2: 2000 Dd:Cc
Checksum
19-5