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MLS Cache Fast Aging Time
The processing of the MLS cache entries can cause performance problems on your switch. To keep this
situation under control, it’s good practice to monitor the IP cache and make sure it remains well under the
maximum size of 128K. Doing so will prevent cache entries from being dropped continuously.
You can keep the size of the cache more manageable by having the MLS cache prune entries that are no
longer needed. This type of pruning is known as fast aging time. This method configures a timer that checks
for a certain number of packets to be sent for a flow during the configured amount of time. If the flow has not
sent at least the configured number of packets during the configured time, the entries for the flow are dropped.
Fast aging time is good for one−time−use entries, such as those used for DNS lookups and Trivial File
Transfer Protocol (TFTP) transfers.
VLAN ID
MLS requires that inter−VLAN routing and packet−forwarding decisions be based on which VLANs have
been configured on the ports. The internal route processors (such as the MSM, MSFC, RSM, and RSFC) use
only VLAN IDs to identify their interfaces—it is not necessary to configure a VLAN ID for them.
An external route processor has no knowledge about VLANs, because these devices are configured using
subnets. A VLAN ID must be assigned to them, if they are to participate in MLS. The interface on the
external route processor must be an Ethernet or Fast Ethernet interface. You cannot configure the VLAN ID
on a sub−interface.
VTP Domain
While configuring MLS, it is important to determine which of the MLS−RP interfaces will be MLS interfaces,
and to add them to the VTP domain of which your other MLS switches are members. Remember, a switch can
be a member of only one domain, and any interfaces participating in MLS on the switch or router must be
configured members of that domain.
Management Interfaces
Only one interface on an MLS−RP needs to be configured to provide MLS management. The MLS
management interface advertises MLSP hello messages, route changes, VLAN information, and MAC
addresses. You must specify one of the MLS−RP’s interfaces as a management interface, or MLSP packets
will not be sent or received.
The management interface can be any MLS interface connected to the MLS switch. More than one
management interface can be configured; however, doing so is unnecessary and only adds to the management
overhead for the MLS−RP.
Configuring an External MLS Route Processor
Configuring the MLS−RP for MLS involves the following tasks:
Enabling MLSP on an MLS−RP•
Adding the VLAN ID to the router interface•
Adding the MLS interface to the VTP domain•
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