Wednesday, October 20, 2004

cisco port chanelling / Trunking how-to

Here's how i channeled 2 ports of a 2950G and 2970G.

The hostname is same as the model number.

Some theory for thrunking before we proceed ahead.

A point-to-point link configured on a single Fast-Ethernet, Gigabit Ethernet, or Fast- or Gigabit EtherChannel bundle and another network device, such as a router or second switch. Trunks transport the packets of multiple VLANs over a single network link.

The available trunking encapsulation types for Ethernet are:

Inter-Switch Link (ISL) - a Cisco-proprietary trunking encapsulation that adds a 26-byte header and 4-byte trailer to the frame.
IEEE 802.1Q (dot1q)- an industry-standard trunking encapsulation that does not change the size of the frame. Because multiple vendors support dot1q, it is becoming more common in newer switched networks.
Negotiate - The port negotiates with its neighbor port to mirror its encapsulation configuration, either ISL (preferred) or 802.1Q trunk. This configuration option is only available in switch software release 4.2 and later.
There are five trunking modes:

On - Forces the port to become a trunk port, even if the neighboring port does not agree to the change.
Off – Forces the port to become non-trunking, even if the neighboring port does not agree to the change.
Desirable - Causes the port to actively seek to convert the link to a trunk. The port becomes trunked if the neighboring port is set to either “on”, “desirable”, or “auto” modes.
Auto - Makes the port available to serve as a trunk link. The port becomes a trunk port if the neighboring port is set to either “on” or “desirable” modes. This is the default mode for both Fast- and Gigabit Ethernet ports.
Nonegotiate - Puts the port into permanent trunking mode but the neighboring port must be manually configured as a trunk port in order to establish a trunk.
Trunking Facts:

For trunking to be auto-negotiated on Fast Ethernet and Gigabit Ethernet ports, the ports must be in the same VTP domain.
Not all switches support all encapsulation methods; for instance the Cat2948G and Cat4000 series switches support only 802.1Q encapsulation. In order to determine whether a switch supports trunking, and what trunking encapsulations are supported, look to the hardware documentation or use the "show port capabilities" command.
For trunking to be enabled on EtherChannel bundles the speed and duplex settings must be configured the same on all links. If part of an EtherChannel bundle fails, traffic will still be passed, but at a slower rate.

The Blow 2 Commands would do the trick.

The 2950G supports only dot1q and willnot give you an option.

Before you do anything Just in cable on one of the ports and very the switches can talk to each other and check the

2950G# show cdp neighbour detail

This should show the other 2970G as the neighbour along with other information.

On the 2950G enter the commands below going to the ports you need to channel

2950G(config-if)# switchport mode trunk

On the 2970G enter the commands below going to the ports you need to channel

2970G(config-if)# switchport trunk encapsulation dot1q (you can use isl too if the other switch supports it)
2970G(config-if)# switchport mode trunk

Just Plug in the second cable on the ports configured and within some time it will bring up the channel. If you feel that the channel has not come up and its causing a packet storm then you can pull off one of the cable and you are back to normal.

The command to verify that the channel is up is :

2950G# show trunk
2970G# Show trunk

Soon would be putting on how to channel in enhanced IOS switches like 2948 and how to channel router interface and switch ports.

Manage you growing bandwidth the smart way. Nitin :)

3 Comments:

At 10/25/2009 09:18:00 PM, Blogger Adi said...

Thank you for sharing.
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