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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Let’s examine each of these tasks, as well as how to disable each of these features in case they are no longer needed on an interface.

Enabling MLSP on an MLS−RP for IP

To enable the MLSP that runs between the MLS−SE and the MLS−RP, enter the following command in Global Configuration mode:

MLS−RP(config) mls rp ip

Disabling MLSP on an MLS−RP for IP

To disable MLSP on an interface, use the following command in Global Configuration mode:

MLS−RP(config) no mls rp ip

Enabling MLSP on an MLS−RP for IPX

If you are using version 12.0 or later of the Cisco IOS, you can also enable MLSP to multilayer−switch IPX packets. To do so, use the following command:

MLS−RP (config) mls rp ipx

Disabling MLSP on an MLS−RP for IPX

To disable MLSP for IPX, use the following command:

MLS−RP (config) no mls rp ipx

Assigning a VLAN ID

To configure a VLAN ID for an external router’s interface, enter the following command:

mls rp vlan−id <vlan−id−num>

For example, here is how to assign VLAN 3 to an interface:

1. Enter the interface for which you want to assign the VLAN ID by using the following command:

Router(config) interface fastethernet 1/1

2. To add the VLAN ID for VLAN 3, use the following command:

Router(config−if) mls rp vlan−id 3

Adding an MLS Interface to a VTP Domain

Enter the following command to add an interface to a VTP domain:

mls rp vtp−domain <domain−name>

Here is an example of how to use this command:

1. Enter the interface for which you want to assign the VLAN ID:

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