Etherchannel: 3550-1

Etherchannel: 3550-1

by Cyrus Lok on Saturday, May 29, 2010 at 2:55am

I have attempted to bundle fa0/1, fa0/3 and fa0/5 to be etherchannel group 1

There should have an increase in bandwidth, however it does not seem to be the case.

fa0/3 and fa0/5 are suspended due to incompatibility with fa0/1 and hence even if bundled up po1 is still having a value of 19 which means it is still 100mbps….

3550-1#sh spanning-tree vlan 1

VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 000b.be08.f480
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 4097 (priority 4096 sys-id-ext 1)
Address 000b.be08.f480
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 15

Interface Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
Po1 Desg FWD 19 128.65 P2p

Interface status command shows fa0/3 and fa0/5 were suspended:
3550-1#sh int status

Port Name Status Vlan Duplex Speed Type
Fa0/1 connected trunk a-full a-100 10/100BaseTX
Fa0/2 notconnect 1 auto auto 10/100BaseTX
Fa0/3 suspended 1 a-full a-100 10/100BaseTX
Fa0/4 notconnect 1 auto auto 10/100BaseTX
Fa0/5 suspended 1 a-full a-100 10/100BaseTX

This is because by default 3550 have trunk encapsulation set to ISL, 2950 switch only supports dot1q, so I will need to remedy this in fa0/3 and fa0/5

3550-1(config)#int fa0/3
3550-1(config-if)#switchport trunk encapsulation dot1q

Check the status of fa0/3 again:
3550-1(config-if)#do sh int status

Port Name Status Vlan Duplex Speed Type
Fa0/1 connected trunk a-full a-100 10/100BaseTX
Fa0/2 notconnect 1 auto auto 10/100BaseTX
Fa0/3 connected trunk a-full a-100 10/100BaseTX
Fa0/4 notconnect 1 auto auto 10/100BaseTX
Fa0/5 suspended 1 a-full a-100 10/100BaseTX

as shown in the command, fa0/3 is connected.

3550-1(config-if)#do sh ether 1 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: 1
Number of aggregators: 1

Group Port-channel Protocol Ports
——+————-+———–+———————————————–
1 Po1(SU) LACP Fa0/1(P) Fa0/3(P) Fa0/5(s)

Ok, from this summary fa0/5 is shown to be suspended.

3550-1#sh spanning-tree vlan 1

VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 000b.be08.f480
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 4097 (priority 4096 sys-id-ext 1)
Address 000b.be08.f480
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300

Interface Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
Po1 Desg FWD 12 128.65 P2p

The cost value has been reduced! Which is correct, because fa0/1 and fa0/3 are bundled up together successfully and hence more bandwidth.

Cisco’s warning is really very clear, sweet.

3550-1(config-if)#switchport trunk encapsulation dot
3550-1(config-if)#
*Mar 1 00:17:06.891: %EC-5-CANNOT_BUNDLE2: Fa0/5 is not compatible with Fa0/1 and will be suspended (trunk mode of Fa0/5 is access, Fa0/1 is trunk)

3550-1#sh int fa0/5 switchport
Name: Fa0/5
Switchport: Enabled
Administrative Mode: dynamic desirable
Operational Mode: down (suspended member of bundle Po1)
Administrative Trunking Encapsulation: dot1q
Negotiation of Trunking: On

fa0/5 is in dynamic desirable… strange.. it should be a trunk, because fa0/3 of 2950 has set to nonegotiate hence fa0/5 cannot be negotiated to be a trunk.

3550-1(config-if)#switchport mode trunk
3550-1(config-if)#
*Mar 1 00:18:52.127: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/5, changed state to up

Now fa0/5 is a trunk and encapsulation is dot1q, all works fine. Let’s verify again.
3550-1#sh etherchannel 1 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: 1
Number of aggregators: 1

Group Port-channel Protocol Ports
——+————-+———–+———————————————–
1 Po1(SU) LACP Fa0/1(P) Fa0/3(P) Fa0/5(P)

No more suspended interface!

3550-1#sh spanning-tree vlan 1

VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 000b.be08.f480
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 4097 (priority 4096 sys-id-ext 1)
Address 000b.be08.f480
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300

Interface Role Sts Cost Prio.Nbr Type
——————- —- — ——— ——– ——————————–
Po1 Desg FWD 9 128.65 P2p

3550-1#

Cost value has been reduced to 9, this means all ports have been bundled successfully and yields a bandwidth of up to 300mbps.

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