14-14
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 14 Configuring MLS
Configuration Guidelines and Restrictions
Maximum Transmission Unit Size
The default maximum transmission unit (MTU) for IP MLS is 1500. To change the MTU on an IP
MLS-enabled interface, enter the ip mtu mtu command.
Restrictions on Using IP Routing Commands with IP MLS Enabled
Enabling certain IP processes on an interface will affect IP MLS on the interface. Table 14-5 shows the
affected commands and the resulting behavior.
IP MMLS
These sections describe the IP MMLS configuration guidelines:
• IP MMLS Supervisor Engine Guidelines and Restrictions, page 14-14
• IP MMLS MSFC Configuration Restrictions, page 14-15
• Unsupported IP MMLS Features, page 14-15
IP MMLS Supervisor Engine Guidelines and Restrictions
This section describes the guidelines and restrictions for configuring Supervisor Engine 1 for IP MMLS:
• Only the ARPA rewrites are supported for the IP multicast packets.
• The Subnetwork Address Protocol (SNAP) rewrites are not supported.
• You must enable one of the multicast services (IGMP snooping or GMRP) on the switch in order to
use IP MMLS.
• The IP multicast flows are not multilayer switched if there is no entry in the Layer 2 multicast
forwarding table (for example, if no Layer 2 multicast services are enabled or the forwarding table
is full). Enter the show multicast group command to check for a Layer 2 entry for a particular IP
multicast destination.
• If a Layer 2 entry is cleared, the corresponding Layer 3 flow information is purged.
• When using two MSFCs that have one or more interfaces in the same VLAN, the switch uses two
reserved VLANs (VLANs 1012 and 1013) internally to forward the multicast flows properly.
• The MSFC will not act as an external router for a Catalyst 5000 family switch that has Layer 3-
switching hardware.
Table 14-5 IP Routing Command Restrictions
Command Behavior
clear ip route Clears all MLS cache entries for all switches performing Layer 3
switching for this MSFC.
ip routing The no form purges all MLS cache entries and disables IP MLS
on this MSFC.
ip security (all forms of this
command)
Disables IP MLS on the interface.
ip tcp compression-connections Disables IP MLS on the interface.
ip tcp header-compression Disables IP MLS on the interface.
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