Category Archives: 02) SWITCH 300-115

SWITCH 300-115 1.5 Configure and verify EtherChannels

1.5.a LACP, PAgP, manual
Etherchannel comes in three flavors, on, my preference often called static or manual,  whereby there is no negotiation of the channel and thus, no extra protocol traffic, PAGP or port aggregation protocol which is Cisco proprietary, and LACP or link aggregation protocol which is the open standard 802.3ad. It is interesting to note that PAGP is not supported on Cisco’s Nexus OS line and that LACP is the preferred method of aggregation from the data center side of the house.
They all have one thing in common, however, and that is to bundle together a group of ports on a switch with the net effect of increasing bandwidth between two connected switches. For instance switches will support 2 to  8 active members on each side of a connection; so considering they are 100 Meg each, a total of 1600 Meg bandwidth can be achieved between them.

Another 8 ports may be used as backup but only 8 may be active at one time. The aggregated ports of a channel must be setup on the individual switch but the ports do not have to be contiguous, and they can cross modules in the event of a chassis type switch or a stack. Also the channel numbers on either side do not have to match, but I advise making it a practice of matching the sides as it makes for easier documentation, and more intuitive troubleshooting.

Another inherent benefit is lessening the impact of Spanning-tree on the network. The etherchannel or port-channel is treated as a single link by STP, therefore there can be no blocking of individual links within the channel, although multiple redundant channels between switches would still be governed by spanning-tree.
A caveat in the creation of a channel is that both sides port configurations need to be exactly the same or the channel will not form. This is one reason why care should be taken when using on or manual mode because without negotiation, there will be no warning in the event of misconfiguration. Another thing to keep in mind is that there is no mixing of channel protocols. For instance, PAGP can use desirable/auto, desirable/desirable, but not auto/auto, similar to DTP. LACP can be act/passive, active/active but not passive/passive. On mode is simply on for both sides.

SWITCH 300-115 1.4 Configure and verify trunking

1.4.a VTPv1, VTPv2, VTPv3, VTP pruning

1.4.d Manual pruning

Before I get to manual pruning, VTP version 3 deserves a mention.

VTP version 3 comes with a bit of an upgrade that sets itself apart from earlier versions, to wit:

Version 3 now supports extended range vlans and private vlans.
The vtp database can support other formats, ie, MST.
Precautions against database hijacking, ie, inserting a switch with a higher revision number
   can’t whack the existing database because only the primary vtp domain server may make
Hidden and secret passwords are available, not just plain text
Version 3 can be configured per port instead of only globally as in earlier versions.

Version 3  offers optimized resource handling and more efficient information transfer, whatever that means. (Sounds like marketing)

Let’s look at vtp version 3.

From enable mode make the vtp server the primary vtp server. See below:
Then continue as for the earlier versions, except for the password. Hidden and secret are now
SW1(config)#vtp password ccie secret
VTP secret has to be 32 characters in length
SW1(config)#vtp password ccie hidden
Setting device VTP password
As discussed earlier in the VTP section, VTP pruning in my estimation is about the only good thing to come from the whole VTP mess.
Manual pruning is what it says; manual. If you are not using VTP pruning to limit unnecessary broadcasts then you will want to prune vlans that are not in use, by hand.

SWITCH 300-115 1.4 Configure and verify trunking

1.4.d Manual pruning

from switch flg pg 66

On trunk links, it is recommended to manually prune the VLANs that are not used.
You can use VTP pruning if VTP is in use, but manual pruning (using a switch-
port trunk allowed VLAN) is a secure way of allowing only those VLANs that are
expected and allowed on the link. In addition to this, it is also a good practice to
have an unused VLAN as a native VLAN on the trunk links to prevent DTP spoof-