Port aggregation protocol (PAgP) is a Cisco-proprietary protocol for managing EtherChannels. If a VSS MEC terminates to a Cisco switch, you can run PAgP protocol on the MEC. If PAgP is running on the MECs between the VSS and an upstream or downstream switch, the VSS can use PAgP to detect a dual-active scenario. The MEC must have at least one port on each switch of the VSS.
In virtual switch mode, PAgP messages include a new type length value (TLV) which contains the ID of the VSS active switch. Only switches in virtual switch mode send the new TLV.
For dual-active detection to operate successfully, one or more of the connected switches must be able to process the new TLV. Catalyst 4500, Catalyst 4500-X, and Catalyst 49xx series switches have this capability. For a list of other Cisco products that support enhanced PAgP, refer to Release Notes for Cisco IOS Release at this URL:
When the VSS standby switch detects VSL failure, it initiates SSO and becomes VSS active. Subsequent PAgP messages to the connected switch from the newly VSS active switch contain the new VSS active ID. The connected switch sends PAgP messages with the new VSS active ID to both VSS switches.
If the formerly VSS active switch is still operational, it detects the dual-active scenario because the VSS active ID in the PAgP messages changes. This switch initiates recovery actions as described in the "Recovery Actions" section.
An VSS active switch that detects a dual-active condition shuts down (by err-disabling) all of its non-VSL interfaces to remove itself from the network, and waits in recovery mode until the VSL links have recovered. You might need to intervene directly to fix the VSL failure. When the shut down switch detects that VSL is operational again, the switch reloads and returns to service as the VSS standby switch.
Loopback interfaces are also shut down in recovery mode. The loopback interfaces are operationally down and not err-disabled.
This is actually a pretty cool feature, i didn't even know it existed until I was looking for a solution to advertise a subnet (prefix in BGP talk), only if a certain condition existed. This is exactly what conditional advertisements does
j ai une question j ai achete un routeur cisco 887VA-k9 , je le configuré avec la configuration ci- dessous
si je le lier avec mon pc portable sur l un de ses ports directement ça marche toute est bien ( la connexion internet + m...
Attached policy provides CLI access to the Cisco 4G router over text messaging. Two files are in the attached .tar file:
2. PDF with instructions on how to load and use the .tcl file.