On most Cisco switches it is possible to create logical connections that are made-up off different physical interface. It is required that these interfaces share the same speed.
Most Cisco switches support a maximum of 64 EtherChannels. These interfaces do not need to be contiguous, or even within the same module. Each channel must be made up of a minimum of 2, and a maximum of 8 interfaces. Best practice is to use groups of 2, 4 or 8 interfaces. This will provide optimum load-balancing.
The load-balancing can be bases on layer 2, 3 or 4 information. Having different load-balancing methods for different EtherChannels on a single switch is not permitted. Changes to the load-balancing method are applicable for all EtherChannels.
The load-balancing method can be:
The objective of this lab is to understand and learn to configure EtherChannel, Link Aggregation Control Protocol (LACP), and Port Aggregation Protocol (PAgP). In this lab we will use Cisco’s Packet Tracer to configure multiple EtherChannels and implement LACP and PAgA between four Cisco Catalyst switches.
Link aggregation is a computer networking term to describe various methods of combining (aggregating) multiple network connections in parallel to increase throughput beyond what a single connection could sustain, and to provide redundancy in case one of the links fails.
Link aggregation addresses two problems with Ethernet connections: bandwidth limitations and lack of resilience.
With regard to the first issue: bandwidth requirements do not scale linearly. Ethernet bandwidths historically have increased by an order of magnitude each generation: 10 Megabit/s, 100 Mbit/s, 1000 Mbit/s, 10,000 Mbit/s. If one started to bump into bandwidth ceilings, then the only option was to move to the next generation which could be cost prohibitive. An alternative solution, introduced by many of the network manufacturers in the early 1990s, is to combine two physical Ethernet links into one logical link via channel bonding. Most of these solutions required manual configuration and identical equipment on both sides of the aggregation.
The second problem involves the three single points of failure in a typical port-cable-port connection. In either the usual computer-to-switch or in a switch-to-switch configuration, the cable itself or either of the ports the cable is plugged into can fail. Multiple physical connections can be made, but many of the higher level protocols were not designed to failover completely seamlessly.
Port Aggregation Protocol (PAgP) is a Cisco Systems proprietary networking protocol, which is used for the automated, logical aggregation of Ethernet switch ports, known as an EtherChannels. This means it can only be used between Cisco switches and/or switches from licensed vendors. A similar purpose protocol known as LACP, released by the IEEE known as 802.3ad, is an industry standard and is not tied to any specific vendor.
PAgP can be configured on a Cisco switch to operate in three different modes.
- auto: Passive negotiation of the channel.
- desirable: Active negotiation of the channel.
- on: No protocols are used, it assumes the other side has also enabled link aggregation.
PAgP aids in the automatic creation of EtherChannel links. PAgP packets are sent between EtherChannel-capable ports in order to negotiate the formation of a channel. Some restrictions are deliberately introduced into PAgP. The restrictions are:
PAgP does not form a bundle on ports that are configured for dynamic VLANs. PAgP requires that all ports in the channel belong to the same VLAN or are configured as trunk ports. When a bundle already exists and a VLAN of a port is modified, all ports in the bundle are modified to match that VLAN.
PAgP does not group ports that operate at different speeds or port duplex. If speed and duplex change when a bundle exists, PAgP changes the port speed and duplex for all ports in the bundle.
PAgP modes are off, auto, desirable, and on. Only the combinations auto-desirable, desirable-desirable, and on-on allow the formation of a channel. The device on the other side must have PAgP set to on if a device on one side of the channel does not support PAgP, such as a router.
PAgP Configuration Example:
- Switch# configure terminal
- Switch(config)# interface range fastethernet 0/4 – 5 (Note: Spaces are mandatory.)
- Switch(config-if)# no switchport
- Switch(config-if)# no IP address
- Switch(config-if)# channel-group 1 mode [auto/desirable/on]
- Switch(config-if)# end
Perform Basic Router Configuration as follows:
- Configure the hostname on all routers and switched as shown in the network diagram.
- Configure no ip domain-lookup on all routers and switches.
- Configure the enable secret password as cisco on all routers and switches.
- Configure the console and vty password as sanfran on all routers and switches.
- Configure the exec-timeout command to the console and virtual terminal lines.
- Save the running configuration to the NVRAM.
- Configure all switches to be part of the VTP domain “CCNP” with the password of “cisco”.
- Configure all switches to run VTP version 2.
- Configure switches DSW1 and DSW2 as VTP servers.
- Configure switches ASW1 and ASW2 as VTP clients.
Configure EtherChannel trunks on the switches as shown in the network diagram. Only switches DSW1 and DSW2 should actively initiate channel establishment; switches ASW1 and ASW2 should be configured as passive links that should not actively attempt to establish an EtherChannel. The EtherChannels should be configured as follows:
- The two ports between DSW1 and DSW2 belong to channel group 1 and use mode on.
- The two ports between DSW1 and ASW1 belong to channel group 2 and use LACP.
- The two ports between DSW1 and ASW2 belong to channel group 3 and use PAgP.
- The two ports between DSW2 and ASW1 belong to channel group 4 and use LACP.
- The two ports between DSW2 and ASW2 belong to channel group 5 and use PAgP.
- On DSW1 VLANs 10, 20, 30, and 40.
- Confirm that the above VLANs have propagated to all switches.
- Assign port connecting PCs and Servers to VLANs as shown in the network diagram.
Spanning Tree Configuration:
- Configure DSW1 as the primary Root Bridge for all VLANs.
- Configure DSW2 as the secondary Root Bridge for all VLANs.
Download this lab now: Configuring PortChannel (330.4 KiB, 1,377 hits)
Configuring PortChannel (330.4 KiB, 1,377 hits)