Tag Archives: SWITCH 300-115 1.5a

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 1.5 Configure and verify EtherChannels

1.5.a LACP, PAgP, manual


For CCNP Switch it is advisable to get some switches. Two should be enough to get you through. 3560 minimum, (and so cheap on ebay) which will support everything you need.

Make redundant links between your switches as in the diagram.

set up etherchannel between the 4 switches. I chose on mode to begin; config below:


the mode is “on”, f0/11 and 12 are bundled layer 2 and up. to prove that, if you mismatch link configurations between ports, see below suspended port f0/11:


adding storm-control suspended f0/11. So make them the same on both sides and be especially careful in production if you are not using negotiation or etherchannel guard.

Make a PAGP etherchannel between a different set of links:

sw2(config)#int range f0/11 – 12
sw2(config-if-range)#no channel-g 1 mode on
sw2(config-if-range)#channel-g 1 mode desir


make another set of links an LACP channel (note the wait below):

sw1(config)#int rang f0/7 – 8
sw1(config-if-range)#channel-g 2 mode act
sw1(config-if-range)#do sh etherchann summ | b G
Group  Port-channel  Protocol    Ports
1      Po1(SU)         PAgP      Fa0/11(P)   Fa0/12(P)
2      Po2(SU)         LACP      Fa0/7(w)    Fa0/8(w)
3      Po3(SU)          –             Fa0/9(P)    Fa0/10(P)

sw1(config-if-range)#do sh ether summ
Flags:  D – down        P – bundled 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

M – not in use, minimum links not met
u – unsuitable for bundling
w – waiting to be aggregated
d – default port

Number of channel-groups in use: 3
Number of aggregators:           3

Group  Port-channel  Protocol    Ports
1      Po1(SU)         PAgP      Fa0/11(P)   Fa0/12(P)
2      Po2(SU)         LACP      Fa0/7(P)    Fa0/8(P)
3      Po3(SU)          –             Fa0/9(P)    Fa0/10(P)

i made them both desirable, and active on both ends, but you could choose desirable/auto active/passive between the two pair, just not auto/auto nor passive/passive…

but you knew that…

try the command show etherchannel port…