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Cisco IOS to CatOS Etherchannel Configuration

James — Mon, 29 Oct 2007 19:02:43 +0000

Here are the relevant parts of the configuration to setup an etherchannel between an IOS device and a CatOS device. First lets start with the CatOS device, in this case a 6509. We will be using ports 3/9 and 3/10.

We first need to set the ports we want to use to be a trunk. Here we are forcing dot1q.

6509#set trunk 3/1-2 nonegotiate dot1q

Now we need to setup the port channels. These channels will be used as 1 and aggregate bandwidth between them.

6509#set port channel 3/9-10

Note: There is an option at the end of this command to specify the admin group. This is how the CatOS groups the ports. If you do not specify the admin group, the CatOS will automatically assign one. This is something to watch out for if you set each port separately.

Now, turn the port channel on.

6509#set port channel 3/9-10 mode on

That is it for the CatOS. The config for the IOS is quite a bit different. First, create a port channel interface and make it a trunk.

3750(config)#interface port-channel 1
3750(config-if)#switchport trunk encapsulation dot1q
3750(config-if)#switchport mode trunk

Assign ports to the port channel group.

3750(config)#interface GigabitEthernet1/0/1
3750(config-if)#channel-group 1 mode on
3750(config-if)#interface GigabitEthernet1/0/2
3750(config-if)#channel-group 1 mode on

Just connect the ports and everything should come up. To check on the CatOS.

6509#show port channel
Port Status Channel Admin Ch Mode Group Id
—– ———- ——————– —– —–
3/9 connected on 746 1734
3/10 connected on 746 1734

Port Device-ID Port-ID Platform
—– ——————————- ————————- —————-
3/9 3750 GigabitEthernet1/0/1 cisco WS-C3750-48P
3/10 3750 GigabitEthernet1/0/2 cisco WS-C3750-48P

Here, both ports 3/9 and 3/10 show as connected and on the same admin channel.

And for the IOS.

3750#show etherchannel summary
Flags: D – down P – 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
u – unsuitable for bundling
w – waiting to be aggregated
d – default port

Number of channel-groups in use: 1
Number of aggregators: 1

Group Port-channel Protocol Ports
——+————-+———–+———————————————–
1 Po1(SU) – Gi1/0/1(P) Gi2/0/1(P)

The last line is the important one. Notice that is shows both ports are in port channel 1.

To configure and IOS to IOS etherchannel, just repeat the exact steps for the IOS on the second switch.
That’s all there is to it.

Adding a Cisco switch to a VTP domain

James — Wed, 17 Oct 2007 05:09:27 +0000

Adding a switch to a VTP domain is fairly easy to do, but done incorrectly, can bring down a whole network. Fortunatly I have not had this happen to me, but I have heard horror stories. There are a few simple steps to take to make sure everything stays running smoothly.

The very first step to complete as soon as you are ready to put a new switch on a network and join it to the domain, is to make sure that the vtp mode is set to transparent. Setting the mode to transparent ensures that the “Configuration Revision” is set to 0. If the switch has been used in a lab and has vlans configured and a configuration revision that is higher than the domain server, even if the switch being added is in client mode, it will overwrite the server and propagate all of it’s vlans across the network.

This is directly taken from Cisco’s website:

A recently added switch can cause problems in the network. It can be a switch that was previously used in the lab, and a good VTP domain name was entered. The switch was configured as a VTP client and was connected to the rest of the network. Then, you brought the trunk link up to the rest of the network. In just a few seconds, the whole network can go down.

If the configuration revision number of the switch that you inserted is higher than the configuration revision number of the VTP domain, it propagates its VLAN database through the VTP domain.

This occurs whether the switch is a VTP client or a VTP server. A VTP client can erase VLAN information on a VTP server. You can tell this has occurred when many of the ports in your network go into the Inactive state but continue to assign to a nonexistent VLAN.

To make sure this does not happen, before you connect the switch to the network, make sure to set the vtp mode to transparent.

C3750-Client(config)#vtp mode transparent
C3750-Client(config)#exit
C3750-Client#show vtp status
C3750-Client#sh vtp status
VTP Version : 2
Configuration Revision : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs : 7
VTP Operating Mode : Transparent
VTP Domain Name :
VTP Pruning Mode : Disabled
VTP V2 Mode : Disabled
VTP Traps Generation : Disabled
MD5 digest : 0×18 0×17 0xE9 0×22 0×49 0×96 0×0C 0×7E
Configuration last modified by 10.10.10.20 at 3-1-93 00:03:25

Now that this switch won’t overwrite the server, configure the vtp domain and password, and then change the mode to client.

C3750-Client(config)#vtp domain Test
Changing VTP domain name from NULL to Test
C3750-Client(config)#vtp password Testpassword
C3750-Client(config)#vtp mode client
Setting device to VTP CLIENT mode

Show the vtp status to confirm.

C3750-Client#show vtp status
VTP Version : 2
Configuration Revision : 62
Maximum VLANs supported locally : 1005
Number of existing VLANs : 38
VTP Operating Mode : Client
VTP Domain Name : Test
VTP Pruning Mode : Enabled
VTP V2 Mode : Enabled
VTP Traps Generation : Disabled
MD5 digest : 0xCD 0×9D 0xFF 0xC3 0×6F 0×63 0×5F 0xF5
Configuration last modified by 10.10.10.2 at 10-16-07 22:16:43

And then a show vlan and check the output to make sure all the vlans have propagated.

C3750-Client#show vlan

The only rule you really need when adding switches is to make sure the switch is in TRANSPARENT mode first.

Configuring a VTP domain on Cisco switches

James — Wed, 17 Oct 2007 04:45:00 +0000

VTP domains allow you to manage all of your vlans from a central switch. This can be a great tool if you are dealing with a large number of vlans spread out over multiple switches. There are a couple of issues that you must be careful of when you implement a vtp domain, which I will go over shortly.

The first requirement is to make sure that your trunks between switches are up and working.

C3750-Payment#show interface trunk

And the output should look something like:

C3750-Payment#sh int trunk
Port Mode Encapsulation Status Native vlan
Fa2/0/48 on 802.1q trunking 1

Port Vlans allowed on trunk
Fa2/0/48 1-4094

Port Vlans allowed and active in management domain
Fa2/0/48 1-2,4,6,8,10,12,16-37,102-103,256-258

Port Vlans in spanning tree forwarding state and not pruned
Fa2/0/48 1-2,4,6,8,10,12,16-37,102-103,256-258

If there are not any ports listed as a trunk, that needs to be fixed before proceeding. Now that we know the switches are communicating, we can proceed to look at the current vtp configuration.

C3750-Payment#show vtp status

And you should get:

C3750-Payment#sh vtp status
VTP Version : 2
Configuration Revision : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs : 7
VTP Operating Mode : Transparent
VTP Domain Name :
VTP Pruning Mode : Disabled
VTP V2 Mode : Disabled
VTP Traps Generation : Disabled
MD5 digest : 0×18 0×17 0xE9 0×22 0×49 0×96 0×0C 0×7E
Configuration last modified by 10.10.10.20 at 3-1-93 00:03:25

If the VTP Operating Mode is not “Transparent” on all of the switches, it needs to be set to transparent to prevent problems later.

C3750-Payment(config)#vpt mode transparent

This will reset the Configuration Revision to 0. It is very important that all switches have the configuration revision reset!

Now, on the switch that you want to be the vtp server; set the domain, password, and then change it to server mode.

C3750-Payment(config)#vtp domain Test
VTP domain Test modified
C3750-Payment(config)#vtp password Testpassword
C3750-Payment(config)#vtp mode server
Setting the device to VTP SERVER mode

Make sure all of the vlans that you need are on this switch. Once they are, setup the other switches as clients.

C3750-Client(config)#vtp domain Test
Changing VTP domain name from NULL to Test
C3750-Client(config)#vtp password Testpassword
C3750-Client(config)#vtp mode client
Setting device to VTP CLIENT mode

Check the VTP status on the client to confirm the vtp status has changed and the vlans have been configured.

C3750-Client#show vlan

Everything is now configured. Vlan additions can now be made on the switch that is in server mode and they will be propagated down to all of the clients.

Adding a switch to an already established vtp domain is basically the same, just make sure to set the switch to transparent mode first. For more details, check Adding a Cisco switch to a vtp domain.

IOS DST Changes Workaround

James — Thu, 22 Feb 2007 14:43:18 +0000

As we all know, 2007 brings a change to the daylight savings time rules. DST will now start on the second Sunday in March and continue until the first Sunday in November. Unfortunatley, using NTP does not resolve this issue because NTP does not carry time zone or summertime information. So to facilitate this change, and to make sure times on network devices remain correct, changes have to be made. On a Cisco device with IOS, there are 2 ways to do this. The first one is to download the patch from Cisco and upgrade the OS. This can be a pain, but there is a simpler way to accomplish this, the clock summer-time command.

Log into the IOS device and enable.

IOSDevice# config t
IOSDevice(config)# clock summer-time CDT recurring 2 Sunday March 02:00 1 Sunday November 02:00 60
IOSDevice(config)# exit

Check the results.

IOSDevice# sh clock detail

Output:

IOSDevice# sh clock detail
12:57:35.142 CST Thu Feb 22 2007
Time source is NTP
Summer time starts 02:00:00 CST Sun Mar 11 2007
Summer time ends 02:00:00 CDT Sun Nov 4 2007

Now everything is ready for the DST change!