Client-To-Server Data Forwarding - Cisco WS-X6066-SLB-APC - Content Switching Module Software Manual

Understanding How ASLB Works

Client-to-Server Data Forwarding

Figure 42-2
events, and
These sections describe the client-to-server data-forwarding paths:
•
•
•
•
Path 1
The first packet from the router has a destination MAC address of the LocalDirector and is on VLAN 10.
The MAC address has an Xtag value of 14 in the Layer 2 table. This value indicates that it requires a
Layer 3 lookup, and the SYN flag is set so the frame goes to port P
In addition to forwarding the frame to port P
Layer 3 forwarding table. This entry is updated later by an "enabler" frame to become a full ASLB
Multilayer Switching (MLS) entry.
Path 2
After receiving the frame from port P
forwards the frame to port P
appropriate server. When this frame enters the switch, it is considered an "enabler" frame. The switch
hardware does a lookup in the Layer 3 table and searches for the entry created by the previous candidate
packet (the packet forwarded through the LocalDirector). If the search was successful, a "hit" occurs in
the Layer 3 table.
Path 3—N
The ASLB MLS entry has been created and the next and subsequent frames from the router with a
destination MAC address of the LocalDirector MAC will be Layer 3 switched unless the packet has
SYN, FIN, or RST flags set or the packet is fragmented.
Path N + 1, N + 2...
On the last frame of a connection, either the FIN or RST flags will be set in the TCP header causing the
packet to go to the LocalDirector. The LocalDirector must then forward the frame back to the switch
after modifying the destination MAC address to be that of the appropriate server. This redirected frame
takes the same path as the first frame of the flow. The FIN packet is used by the LocalDirector as an
indication that the connection with the server has been terminated, and by the ASLB to purge the affected
ASLB MLS entry.
Catalyst 6000 Family Software Configuration Guide—Releases 6.3 and 6.4
42-4
shows how data is forwarded from the router to the servers.
Table 42-3 lists the Layer 3 table entries.
Path 1, page 42-4
Path 2, page 42-4
Path 3—N, page 42-4
Path N + 1, N + 2..., page 42-4
B.
, the switch hardware creates a "candidate" entry in the
A
the LocalDirector makes its standard load-balancing decision and
A,
The LocalDirector changes the destination MAC address to that of the
Chapter 42 Configuring ASLB
Table 42-2 lists the sequence of
.
A
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