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Product Bulletin
© 2008 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information.
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also provide multicast services to customers for which the Cisco Catalyst 4500 acts as a router
running Open Shortest Path First (OSPF) inside the service provider network on separate VLANs.
In addition, service providers have their own control traffic from infrastructure routing and internal
services to maintain and manage network connectivity. This model seems to be common among
service providers. The Cisco Catalyst 4500 model of capturing control traffic using static content
addressable memory (CAM) brings up the various problems related to snooping unwanted control
traffic which wastes precious CPU cycles in addition to doing Layer 2 bridging in software (affects
throughput). The packet could have been bridged in hardware had it not been sent to the CPU.
Per-VLAN CTI addresses this problem by providing a selective per-VLAN path managed mode of
capturing control traffic which can be enabled with global configuration. The corresponding static
CAM entries in the input feature ternary content addressable memory (TCAM) are invalidated in
the new mode. Control packets are captured by feature-specific ACLs attached to VLANs on which
snooping or routing features are enabled.
Auto-MDIX enable/disable CLI:
Auto-MDIX is a feature on 10/100 copper ports that allow the switch to automatically detect the
signaling on the cable from the connected device and operates as either an MDI or MDIX port.
Currently with auto-MDIX, which is enabled permanently or by default on interfaces of some switch
line cards as well as end station network interface cards (NICs), a user can run into problems
when the Ethernet connections at both ends try to do auto-MDIX and neither end is able to decide
which one should be the cross port.
This feature addresses the above problem by introducing a CLI to enable/disable the auto-MDIX
feature on line cards that are auto-MDIX capable. The CLI used to disable this is—“no mdix
auto”, an interface-specific command.
Remote SPAN (RSPAN):
SPAN is a feature that enables the user to analyze network traffic passing through the ports in a
switched network using an RMON probe attached to a switch port. This is done by copying packets
to destination ports as they pass through a source port. In local SPAN, the source ports and
destination ports must exist on the same physical switch. Remote SPAN allows the source ports
and the destination port(s) to be distributed across multiple switches in the network. This is done in
the following manner:
●
A special VLAN called the RSPAN VLAN is set up in the network. Host learning is disabled
in this VLAN to make sure that traffic is flooded to all ports it contains.
●
Traffic from the source ports on a given switch is copied and switched onto the RSPAN
VLAN.
●
The switch(es) with destination ports are configured to copy the traffic on the RSPAN VLAN
out the destination port(s) on the switch(es).
RSPAN, like local SPAN, does not affect the switching of network traffic for any of the source
ports. The RSPAN feature is implemented in hardware and configured by software using the CLI.
ARP QoS:
ARP QoS provides protection of high-priority ARP packets going to a Cisco Catalyst 4500
Supervisor Engine 6-E. This feature is required to help bring up high-priority services such as VoIP
under oversubscribed conditions.