Chapter 1 - Multi Layer Switch

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CCNA Advance

Chapter 1Multilayer Switch


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EtherChannel


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Describing EtherChannel

• Companies require greater and cheaperbandwidth to run their networks

• Users are becoming more impatient withany latency that occurs.

• Cisco originally developed EtherChannelas a LAN switch-to-switch technique of

inverse multiplexing of multiple Fast orGigabit

• Ethernet switch ports into one logicalchannel.

• It is effectively cheaper than higher speed

media while using existing switch ports.


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EtherChannel Features and Benefits

• Logical aggregation of similar links

• Load balances• Viewed as one logical port

• Redundancy


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Describing PAgP and LACP

• PAgP – Port Aggreagation

Protocol:

– Cisco proprietary

• LACP – Link Aggregation

Control Protocol:

– IEEE 802.3ad


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Configuring Layer 2 EtherChannel


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Configuring Layer 3 EtherChannel


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EtherChannel: Guidelines and

Restrictions


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EtherChannel: Guidelines and Restrictions

(Cont.)


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EtherChannel Configuration Guidelines


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Verifying EtherChannel

• Display port Channel information:


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Verifying EtherChannel (Cont.)


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EtherChannel Load Balancing

- EtherChannel balances traffic

load across the links in a channel.- The default and

load balancing method varies

among the Cisco Catalyst models.


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Explaining Multilayer Switching


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Explaining Multilayer Switching

A multilayer switch:

– Combines the functionality

of a switch and a router into

one device

– Enabling the device to switch

traffic when the source and

destination are in the sameVLAN and to route traffic

when the source and

destination are in different

VLANs (that is, different

subnets).


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Layer 2 Switch Forwarding Process


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Layer 3 Switch Forwarding Process


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Explaining Layer 3 Switch Processing


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Layer 3 Switch Processing (Cont.)

Layer 3 switching can occur at two different locations on the

switch.

– Centralized switching: Switching decisions are made on the

route processor by a central forwarding table. – Distributed switching: Switching decisions can be made on a

port or line-card level.

Layer 3 switching takes place using one of these two methods: – Route caching: A Layer 3 route cache is built in hardware as the

switch sees traffic flow into the switch.

– Topology-based switching: Information from the routing table isused to populate the route cache, regardless of traffic.


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Frame Rewrite


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Layer 3 Switch Virtual Interface

You configure an SVI for a VLAN

for the following reasons:

– To provide a default gateway for

a VLAN so that traffic can berouted between VLANs

– To provide fallback bridging if it

is required for non-routable

protocols

– To provide Layer 3 IP connectivity

to the switch

– To support routing protocol andbridging configurations

Inter-VLAN Routing Using Multilayer


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Inter VLAN Routing Using Multilayer

Switch


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Routed Ports on a Multilayer Switch

Physical switch port with Layer 3

capability

• Not associated with a VLAN

• Requires removal of Layer 2 portfunctionality

• Configure

– ip routing

– interface fa0/1• no switchport

• ip address 10.3.3.1

255.255.255.0

– router eigrp 50 (option)• network 10.0.0.0

CEF B d M l il S i h


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CEF-Based Multilayer Switches

CEF caches routing information in the FIB table and Layer 2

next-hop addresses in the adjacency table.

Multilayer Switch Packet Forwarding


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Multilayer Switch Packet Forwarding

Process

• Some IP packets cannot be processed in hardware.

• If an IP packet cannot be processed in hardware, it is

processed by the Layer 3 engine.

CEF B d MLS L k


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CEF-Based MLS Lookups

1. Layer 3 packets initiate TCAM lookup.2. The longest match returns adjacency with rewrite information.

3. The packet is rewritten per adjacency information and forwarded.

ARP Th ttli


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ARP Throttling

ARP throttling consists of these steps:Step 1: Host A sends a packet to host B.

Step 2:The switch forwards the packet to

the Layer 3 engine based on the

“glean” entry in the FIB. A gleanadjacency entry indicates that a

particular next hop should be directly

connected, but there is no MAC

header rewrite information available.

Step 3:The Layer 3 engine sends an

ARP request for host B and installs

the drop adjacency for host B. At this

point, subsequent frames destined

for host B from host A are dropped(ARP throttling).

Step 4: Host B responds to the ARP

request. The Layer 3 engine installs

an adjacency for host B and removesthe drop adjacency.

CEF B d MLS O ti


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CEF-Based MLS Operation

Configuring and Verifying CEF


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Configuring and Verifying CEF

• Configuring CEF

– ip cef (enabled by default)

– ip route-cache cef (only on VLAN interface)

• Verifying CEF – show ip cef fa 0/1 detail

– show adjacency fa 0/1 detail

Verifying CEF


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Verifying CEF

Common CEF Problems


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Common CEF Problems

– Is ideal switching method (CEF, DCEF) in use?

– Are CEF tables complete and accurate?

Verify Layer 3 Switching


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Verify Layer 3 Switching

Displaying Hardware Layer 3 Switching


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Statistics

Adjacency Information


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Adjacency Information

Debugging CEF Operations


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Debugging CEF Operations

How to Troubleshoot CEF


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How to Troubleshoot CEF

Summary


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Summary

• EtherChannel:

– EtherChannel increases bandwidth and provides redundancy by aggregating

individual links between switches.

– EtherChannel can be dynamically configured between switches using either

PAgP or LACP. – Etherchannel is configured and verified using a variety of show commands.

– Best practices should be followed for EtherChannel configuration.

– EtherChannel load balances traffic over all the links in the bundle.

• Multilayer Switch: – Layer 3 switching is high-performance packet switching in hardware.

– MLS functionality can be implemented through CEF.

– CEF uses tables in hardware to forward packets.

– Specific commands are used to enable and verify CEF operations.

– Commands to enable CEF are platform dependent.

– CEF problems can be matched to specific solutions.

– Specific commands are used to troubleshoot and solve CEF problems.

– Ordered steps assist in troubleshooting CEF-based problems.


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Question ?

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Chapter 1 - Multi Layer Switch