Cisco WS-X6066-SLB-APC - Content Switching Module Software Manual page 223

Chapter 13 Configuring CEF for PFC2
In IP unicast and IP multicast traffic, the switch decrements the Layer 3 TTL value by 1 and recomputes
the Layer 3 packet checksum. In IPX traffic, the switch increments the Layer 3 Transport Control value
by 1 and recomputes the Layer 3 packet checksum. The switch recomputes the Layer 2 frame checksum
and forwards (or for multicast packets, replicates as necessary) the rewritten packet to Destination B's
VLAN.
These sections describe how the packets are rewritten:
•
•
•
Understanding IP Unicast Rewrite
Received IP unicast packets are (conceptually) formatted as follows:
Layer 2 Frame Header
Destination
MSFC2 MAC Source A MAC
After the switch rewrites an IP unicast packet, it is (conceptually) formatted as follows:
Layer 2 Frame Header
Destination
Destination B MAC MSFC2
Understanding IPX Unicast Rewrite
Received IPX packets are (conceptually) formatted as follows:
Layer 2 Frame Header
Destination
MSFC2 MAC
After the switch rewrites an IPX packet, it is (conceptually) formatted as follows:
Layer 2 Frame Header
Destination
Destination B
MAC
78-13315-02
Understanding IP Unicast Rewrite, page 13-3
Understanding IPX Unicast Rewrite, page 13-3
Understanding IP Multicast Rewrite, page 13-4
Source
Source
MAC
Source
Source A MAC
Source
MSFC2 MAC
Layer 3 IP Header
Destination Source
Destination B IP Source A IP
Layer 3 IP Header
Destination Source
Destination B IP Source A IP n-1
Layer 3 IPX Header
Checksum/ Destination Net/
IPX Length/ Node/
Transport Control Socket
n Destination B IPX
Layer 3 IPX Header
Checksum/ Destination Net/
IPX Length/ Node/
Transport Control Socket
n+1 Destination B IPX
Catalyst 6000 Family Software Configuration Guide—Releases 6.3 and 6.4
Understanding How Layer 3 Switching Works
TTL Checksum
n calculation1
TTL Checksum
calculation2
Source Net/
Node/
Socket
Source A IPX
Data FCS
Source Net/
Node/
Socket
Source A IPX
Data FCS
Data FCS
Data FCS
13-3