BCMSN Lab - Etherchannel Configuration [CCNP]

(1) Layer 2 Etherchannel: Configuration

Method 1 - If you want to use a negotiation protocol, use the following command:

(a) PAGP

S2#conf t
S2(c0nfig)#int range fa0/3 - fa0/4
S2(config-if)#channel-protocol pagp
S2(config-if)#channel-group [group-no] mode [desirable/auto] (use desirable on at-least 1 side for establishing an etherchannel link)

S4#conf t
S4(config)#int range fa0/3 - fa0/4
S4(config-if)#channel-protocol pagp
S4(config-if)#channel-group [group-no] mode [desirable/auto] (now, we could be either auto or desirable and it would negotiate a link. Let's go 'auto' to have a desirable-auto match here)

Note: It is essential that the same settings are used on both end-to-end switches, i.e: same group-no.

If you do a 'show ip int brief' now you should see 'Port-channel[group-no]' come 'up' (might take a moment or so) at this stage. You can further do the following show Etherchannel commands:

S4#show etherchannel
S4#show etherchannel detail
S4#show etherchannel summary
S4#show etherchannel brief

Alternatively you can choose to implement LACP in the same manner:

(b) LACP

S2#conf t
S2(c0nfig)#int range fa0/3 - fa0/4
S2(config-if)#channel-protocol lacp
S2(config-if)#channel-group [group-no] mode [active/passive] (use active on at-least 1 side for establishing an etherchannel link)

S4#conf t
S4(config)#int range fa0/3 - fa0/4
S4(config-if)#channel-protocol lacp
S4(config-if)#channel-group [group-no] mode [active/passive] (now, we could be either active or passive and it would negotiate a link. Let's go 'passive' to have an active-passive match here)

Note: Again, it is essential that the same settings are used on both end-to-end switches, i.e: same group-no.

and in this way using method 1 you can either:
(a) implement PAGP for negotiating Etherchannel links (on Cisco platform)
or you can:
(b) implement LACP for negotiating Etherchannel links (on cross-compatible platforms)

Method 2 - If you want to hardcode the ports for etherchannel (which is what I personally prefer), you CANNOT use the above 'channel-protocol' command from Method 1. It won't work.

S2#conf t
S2(c0nfig)#int range fa0/3 - fa0/4
S2(config-if)#channel-group [group-no] mode on (notice: on does not have a protocol)

S4#conf t
S4(config)#int range fa0/3 - fa0/4
S4(config-if)#channel-group [group-no] mode on

This hardcodes it as anetherchannel link without using any negotiation (PAGP or LACP).

(2) Layer 3 Etherchannel: Configuration

There is not too much to the config than layer 2.

In layer 3 Etherchannel, we assign an ip-address to the port-channel interface (not the indivitual interfaces) that we created above.

Step 1 is to disable the channel-group extablished on L2 domain. In step 3 we'll re-enable it after we convert port-channel interface in Step 2.

Step 1: Disable channel-group and convert physical interfaces to routed ports.

S2#conf t
S2(config)# int range fa0/3 - fa0/4
S2(config-if)#no channel-group [grp-no]
S2(config-if)#no switchport

Step 2: Convert port-channel interface to routed port and set ip-address.

S2(config-if)#int port-channel[grp-no] (to configure the port-channel[grp-no] interface)
S2(config-if)#? (notice, dhcp snooping and multicast support are only available.-> we'll dig into both of em' later. So, to get more options we conver this port into a routed port using the following cmd:)
S2(config-if)#no switchport (turns of L2 capabilities of the switchport & makes it a L3 interface)
S2(config-if)#ip address 10.1.1.1 255.255.255.0 (assign an ip to the port-channel)

Step 3: Re-enable channel-group (on physical-interfaces)

S2(config-if)#int range fa0/3 - fa0/4
S2(config-if)#channel-group 1 mode [on |active/passive for lacp or|desirable/auto for pagp]

and the same 3 steps are performed on the connected layer 3 switch...

Tip - Servers as of late have started supporting etherchannel too. You can get servers from Dell and order them with multiple network cards that can be 'LACP compliant', meaning we can have a bundled channel, like maybe a 2Gbps interface coming from the server interface to the switch and really having a high bandwidth connection.

Etherchannel: Best practises

-All ports must use same speed and duplex (hard code!)
-Interfaces in a bundle are redundant (If one link goes down, others will still work)
-No interfaces in a bundle can be span ports (span = switchport analyser, which is used to sniff on a switch. This featue cannot be used with etherchannel.)
-Interfaces in bundle must be in the same VLAN or configured as a trunk.
-Any changes to port-channel affects all bundled ports (If we change the configuration under the 'port-channel[grp-no]' interface, it is the umbrella that applies to every single physical interface underneath. But...)
-Any changes to indivitual ports affect only that port (It's not like the port-channel inherits what the configuration is of the physical interface, so suppose if you change the VLAN config of an interface that can't affect the whole bundle by dropping that interface out since it doesn't inherit that into the etherchannel/port-channel interface.)

...and that is the concept of Etherchannel.