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Zorluk: ZorLayer 2 and Layer 3 EtherChannel (LACP)

A network engineer is deploying a point-to-point Layer 3 EtherChannel between two Cisco Catalyst switches, SW-Alpha and SW-Beta.

On SW-Alpha, the engineer issued `no switchport` on physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2, added them to `channel-group 10 mode active`, and then configured `interface Port-channel 10` with `no switchport` and IP address `10.20.30.1 255.255.255.252`.

On SW-Beta, the engineer configured `interface Port-channel 10` with `no switchport` and IP address `10.20.30.2 255.255.255.252`. Next, the physical member interfaces GigabitEthernet0/1 and GigabitEthernet0/2 were assigned to `channel-group 10 mode passive`, but the engineer omitted the `no switchport` command on those physical member interfaces.

Executing `show etherchannel summary` on SW-Beta displays the following output:

text 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 aggregate interface Group Port-channel Protocol Ports ------+-------------+-----------+----------------------------------------------- 10 Po10(SD) LACP Gi0/1(D) Gi0/2(D)

Which configuration oversight on SW-Beta caused Port-channel 10 to exhibit the `SD` (Layer 2, Down) status flags?

  1. The physical member interfaces on SW-Beta were left operating in default Layer 2 switchport mode, preventing them from joining a routed Layer 3 port-channel bundle.Cevap
  2. B
    LACP active mode configured on SW-Alpha is fundamentally incompatible with LACP passive mode configured on SW-Beta.
  3. C
    A native VLAN mismatch exists on the Port-channel 10 trunk interfaces between SW-Alpha and SW-Beta.
  4. D
    The IP address was assigned to the logical Port-channel 10 interface instead of being configured directly on physical interfaces GigabitEthernet0/1 and GigabitEthernet0/2.

Cevap

The physical member interfaces on SW-Beta remained in Layer 2 switchport mode because the 'no switchport' command was omitted on GigabitEthernet0/1 and GigabitEthernet0/2.
For a Layer 3 (routed) EtherChannel to operate correctly, physical member interfaces must be explicitly configured as routed ports using the 'no switchport' command. If physical ports remain in their default Layer 2 switchport state when added to a channel group, they cannot bundle with a routed port-channel interface, resulting in the port-channel defaulting to Layer 2 Down ('SD') status and physical ports marked as Down ('D').

Adım Adım Çözüm

1
Analyze the output flags of 'show etherchannel summary' on SW-Beta.
Port-channel 10 displays flags 'SD', where 'S' indicates Layer 2 (Switchport) and 'D' indicates Down. Member ports Gi0/1 and Gi0/2 are marked with flag 'D' (Down).
Understanding flag meanings allows diagnosing whether the channel is operating as Layer 2 or Layer 3 and identifying port bundling status.
2
Evaluate the configuration differences between SW-Alpha and SW-Beta.
SW-Alpha configured 'no switchport' on both physical member interfaces and the logical port-channel interface. SW-Beta configured 'no switchport' only on the logical Port-channel interface but omitted it on physical member interfaces GigabitEthernet0/1 and GigabitEthernet0/2.
On Cisco Catalyst switches, physical interfaces operate as Layer 2 switchports by default.
3
Determine the operational requirement for Layer 3 EtherChannels.
Physical member interfaces must match the Layer 2/Layer 3 capability of the logical Port-channel interface. When physical ports remain Layer 2 switchports, Cisco IOS prevents them from bundling into a routed Port-channel, driving the Port-channel interface state to Layer 2 Down ('SD').
Applying 'no switchport' to the physical member interfaces before assigning them to the channel group ensures parameter consistency and enables successful LACP bundle establishment.

Anahtar Kavram

Layer 3 EtherChannel Physical Member Interface Requirements
Tahmini Süre:2m 0s
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Konular

Layer 2 and Layer 3 EtherChannel (LACP)

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