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Is It Routing or Is It Layer 3 Switching? YES! Learn It and Use It

Is It Routing or Is It Layer 3 Switching? YES! Learn It and Use It Pete Anderson Steve Stiles Assistant Professor Instructor Davenport University James A Rhodes State College. Agenda. Introductions – 5 minutes What is Layer 3 Switching?– 5 minutes

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Is It Routing or Is It Layer 3 Switching? YES! Learn It and Use It

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  1. Is It Routing or Is It Layer 3 Switching? YES! • Learn It and Use It • Pete Anderson Steve Stiles • Assistant Professor Instructor • Davenport University James A Rhodes State College

  2. Agenda • Introductions – 5 minutes • What is Layer 3 Switching?– 5minutes • How does it relate to Network Design? – 5 minutes • Comparison Routers/L3 Switches – 5 minutes • Technologies – 35 minutes • Hands-On Labs - 35 minutes

  3. Introductions

  4. What is Layer 3 Switching?

  5. Multilayer Switches in Campus Networks • Layer 3 switching speeds approximate that of Layer 2 switches • Hardware-based routing using Application-Specific Integrated Circuits (ASICs) • Make use of TCAM (Ternary Content Addressable Memory) for routing, ACL lookups, policy etc. • Make use of CEF (Cisco Express Forwarding) • RIP, OSPF, and EIGRP are supported • Future: Pure Layer 3 environment leveraging inexpensive L3 access layer switches • Layer 4 switching enables load balancing based on Layer 4 port number • Layer 7 switching uses Network-Based Application Recognition (NBAR) to permit or deny traffic based on data passed by an application

  6. CEF Processing CEF uses special strategies to switch data packets to their destinations expediently. It caches the information generated by the Layer 3 routing engine even before the switch encounters any data flows. CEF caches routing information in one table (FIB) and caches Layer 2 next-hop addresses and frame header rewrite information for all FIB entries in another table, called the adjacency table (AT).

  7. How does it relate to Network Design?

  8. Design Comparisons L2 & L3 • Layer 3 switches usually have packet-switching throughputs in the millions of packets per second (pps) • Traditional general-purpose routers provide packet switching in the range of 100,000 pps to over 1 million pps

  9. Core Layer • Aggregates distribution layer switches. • Implements scalable protocols and technologies and load balancing. • High-speed layer 3 switching using 10-Gigabit Ethernet. • Uses redundant L3 links. For small networks, a core layer is not needed. In this case, the distribution layer switches need to be fully meshed. Recommended practice is to deploy a dedicated core layer to connect 3 or more physical segments or 4 or more pairs of building distribution switches.

  10. Distribution Layer • High availability, fast path recovery, load balancing, QoS, and security • Route summarization and packet manipulation • Redistribution point between routing domains • Packet filtering and policy routing to implement policy-based connectivity • Terminate VLANs • First Hop Redundancy Protocol

  11. Access Layer • Convergence – provides inline Power over Ethernet (PoE) to support IP telephony and wireless access points. • Security – includes port security, DHCP snooping, Dynamic ARP inspection, IP source guard.

  12. Comparison Routers/L3 Switches

  13. Comparison of Routers and L3 Switches Similarities Differences Both routers and multilayer switches use routing protocols or static routes to maintain information about reachability and direction to network destinations (prefixes) and record this information in a routing table. • Routers connect heterogeneous networks and support a wide variety of media and interfaces. Multilayer switches typically connect homogenous networks. Nowadays LAN switches are mostly Ethernet only.

  14. Comparison of Routers and L3 Switches Similarities Differences Perform the same functional packet switching actions: 1. Receive a frame and strip off the Layer 2 header. 2. Perform a Layer 3 lookup to determine the outbound interface and next hop. 3. Encapsulate the packet in a new Layer 2 frame and transmit the frame. • Multilayer switches use specialized hardware to achieve wire-speed Ethernet-to-Ethernet packet switching. • Low- to mid-range routers use multipurpose hardware to perform the packet-switching process. • On average, the packet-switching throughput of routers is lower than the packet-switching throughput of multilayer switches.

  15. Comparison of Routers and L3 Switches Similarities Differences • Routers usually support a wider range of features, mainly because switches need specialized hardware to be able to support certain data plane features or protocols. On routers, you can often add features through a software update.

  16. Technologies

  17. Switched Virtual Interfaces (SVIs) and Routed Ports A Logical Demonstration of a Multilayer Switch:

  18. SVIs Switched Virtual Interfaces

  19. Switch Virtual Interfaces (SVI’s) • Configured on multilayer switches, one per VLAN. • The management interface on an L2 switch is an SVI, but an L2 switch is limited to one active SVI. • An SVI associates with an L2 VLAN – a switch must have an active L2 instance of a VLAN in order for an (L3) SVI to function.

  20. SVI-Based Inter-VLAN Routing Example Switch(config)# ip routing Switch(config)# router rip Switch(config-router)# network 10.0.0.0 Switch(config)# interface vlan 10 Switch(config-if)# ip address 10.10.1.1 255.0.0.0 Switch(config-if)# no shutdown Switch(config-if)# interface vlan 20 Switch(config-if)# ip address 10.20.1.1 255.255.255.0 Switch(config-if)# no shutdown

  21. Layer 2 Etherchannels

  22. EtherChannel Technology • Up to 8 physical links can be bundled into a single logical EtherChannel link. • Usually EtherChannel is used for trunk links. • Configuration applied to port channel interface affects all physical interfaces assigned to the port channel. • Load balancing takes place between the physical links in an EtherChannel.

  23. EtherChannel Management Protocols • Port Aggregation Protocol (PAgP) is a Cisco-proprietary protocol that aids in the automatic creation of Fast EtherChannel links. • Link Aggregation Control Protocol (LACP) is part of an IEEE specification (802.3ad) that also enables several physical ports to be bundled together to form an EtherChannel.

  24. PAgP Modes

  25. LACP Modes

  26. Example: EtherChannel Configuration Switch(config)# interface fastethernet 0/23 Switch(config-if)# channel-group 2 mode active Switch(config)# interface fastethernet 0/24 Switch(config-if)# channel-group 2 mode active Switch(config)# interface port-channel 2 Switch(config-if)# switchport mode trunk Switch(config-if)# switchport trunk native VLAN 99 Switch(config-if)# switchport trunk allowed VLAN 2,3,99 Remote Switch configuration RSwitch(config)# interface fastethernet 0/23 RSwitch(config-if)# channel-group 5 mode on RSwitch(config)# interface fastethernet 0/24 RSwitch(config-if)# channel-group 5 mode on RSwitch(config)# interface port-channel 5 RSwitch(config-if)# switchport mode trunk RSwitch(config-if)# switchport trunk native VLAN 99

  27. Verifying EtherChannel • When several port-channel interfaces are configured on the same device, the show etherchannel summarycommand is useful for displaying one-line information per port-channel. • Layer 2 EtherChannelsare all in use (SU next to the port-channel number). Switch# show etherchannel summary Flags: D - down P - bundled in port-channel I - stand-alone s - suspended H - Hot-standby (LACP only) R - Layer3 S - Layer2 U - in use f - failed to allocate aggregator M - not in use, minimum links not met u - unsuitable for bundling w - waiting to be aggregated d - default port Number of channel-groups in use: 2 Number of aggregators: 2 Group Port-channel Protocol Ports ------+-------------+-----------+-------------------------------------------- 2 Po2(SU) LACP g0/49(P) g0/50(P) g0/51(P) g0/52(P) 7 Po7(SU)LACP g0/47(P) g0/48(P) 9 Po9(SU) PAgP g0/8(P) g0/9(P)

  28. Routed Ports

  29. Routed Ports • Use the no switchportcommand to configure a physical switch port as a routed port. (3560) • Routed ports are used in conjunction with SVI’s. • Routed ports connect point-to-point (L3) links between distribution layer and core layer switches. • A 48-port L3 switch can be configured as a 48-port router.

  30. Routed Port Example Switch(config)# interface GigabitEthernet 1/1 Switch(config-if)# no switchport Switch(config-if)# ip address 10.10.1.1 255.255.255.252 Switch(config-if)# exit ** Switch will let us know when we get forgetful ** Switch(config)# interface GigabitEthernet 1/2 Switch(config-if)# ip address 10.20.1.254 255.255.255.252 % IP addresses may not be configured on L2 links. Switch(config-if)# no switchport Switch(config-if)# ip address 10.20.1.254 255.255.255.252

  31. Layer 3 Etherchannels

  32. L3 EtherChannels • Just as with physical interfaces on multilayer switches, bundles of interfaces (port channels) can be configured as routed ports. • Port channels configured as routed ports are called L3 EtherChannels. • L2 EtherChannels are normally used only when connecting from an access layer switch.

  33. Layer 3 EtherChannel Example

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