Information Technology Reference
In-Depth Information
Figure23-7 TheThreeEssentialsThatMustBeCompleted(UsingMLSP)foraShortcuttoBeCreated:
the Candidate, Enabler, and Caching Steps
Candidate
packet
Enable
packet
Layer 3 switched
A
B
By using the flowmask (essentially an access list), the administrator can adjust the degree of similarity
of these packets, and thus adjust the scope of the flows: destination address; destination and source
addresses; or destination, source, and Layer 4 information. Note that the first packet of a flow always
passes through the router; from then on it is locally switched. Each flow is
unidirectional—communication between PCs, for example, requires the setup and use of
two
shortcuts.
The main purpose of MLSP is to set up, create, and maintain these shortcuts.
These three components (the MLS-RP, the MLS-SE, and the MLSP) free up vital router resources by
allowing other network components to take on some of its functions. Depending on the topology and
configuration, MLS provides a simple and highly effective method of increasing network performance
in the LAN.
Troubleshooting IP MLS Technology
Figure 23-8 is a flow diagram for basic IP MLS troubleshooting. It is derived from the most common
types of MLS-IP cases opened with the Technical Assistance Center (TAC) and faced by our customers
and TAC engineers, up to the time that this document was created. MLS is a robust feature, and you
should have no problems with it. However, if an issue does arise, the following should help you to resolve
the types of IP MLS problems that you might likely face. A few essential assumptions have been made:
•
That you are familiar with the basic configuration steps required to enable IP MLS on the router and
switches, and that you have completed these steps. See the resources listed at the end of this
document for excellent material.
•
That IP routing is enabled on the MLS-RP (it is on by default). If the command
no ip routing
appears in the global configuration of a
show run
, it has been turned off, and IP MLS will not
function.
•
That IP connectivity exists between the MLS-RP and MLS-SE. You can
ping
the IP addresses of the
router from the switch and look for exclamation points (called “bangs”) to be displayed in return.
•
That the MLS-RP interfaces are in an “up/up” state on the router. Type
show ip interface brief
on
the router to confirm this.
Warning
Whenever making configuration changes to a router intended to be permanent,
remember to save those changes with a copy running-config starting-config (shortened
versions of this command include copy run start and wr mem). Any configuration
modifications will be lost if the router reloads or is reset. The RSM, RSFC, and MSFC are
routers, not switches. In contrast, changes made at the switch prompt of a Catalyst 5xxx
or 6xxx family member are automatically saved.
