VLAN Discovery using remote
The first step after ZTP
reload is the discovery of a management VLAN between the User-Facing Premise
(UPE) NID Controller,
such as the Cisco ME 3600X Series Ethernet Access Switch, and one or
Cisco ME 1200 NIDs.
In this step, the LLDP-MED is used to acquire the management VLAN
Cisco ME 1200 NID
can be configured to act either as an end-point or a connectivity link. The
default configuration type is an end-point, where all ports are scanned for
received LLDP-MED broadcast. However, only those ports that have received a
network policy with voice application type are considered. These ports are
configured accordingly, and a VLAN interface is created on the defined VLAN.
If If none of the ports
received LLDP-MED TLVs after 60 seconds, or interface on
UPE NID controller is not configured to
allow a specific management VLAN, ZTP process tries to configure a fallback
VLAN as described below. Hence it is better to check configurations and ensure
there is no network connectivity issue while in this step.
VLAN Discovery in
standalone operating mode
If Cisco ME1200 NID is
UPE NID controller or directly
connected switch upstream, which does not support LLDP-MED Network Policy TLV,
a fallback mechanism is used to complete VLAN discovery. This assumes that an
external DHCP server is present on the network, which can support DHCP Option
60 and 43, and allocate IP address to ME1200 (Note: Option 60 unique identifier
string will be of the form "ME1200-00-3A-99-FD-45-34", where 00:3a:99:fd:45:34
is a sample MAC address of the Cisco ME1200.
The fallback VLAN
discovery can be described as follows:
- When ZTP is triggered using
the push button on Cisco ME 1200 NID, a special, default configuration is
loaded , which includes the following commands:
ztp fallback vlan 1-4095 frame-type tagged interface Gi 1/1-6
ztp fallback vlan 1 frame-type untagged interface Gi 1/1-6
This causes DHCP replies coming from an external DHCP server to be
processed by Cisco ME1200 NID.
- If a DHCP OFFER containing a
VLAN tag in the range of 1-4095, or DHCP OFFER on VLAN 1 (untagged) is received
on any one of the ports 1-6, it is used to determine management VLAN.
- To avoid a flood of DHCP
messages from being intercepted by ME1200, only DHCP replies containing DHCP
Option 60 & 43 are intercepted.
The VLAN that is
determined from this fallback mechanism is used in subsequent steps of the ZTP
fallback VLAN configuration can also be modified by user and the modified
configuration allowed to persist across reloads. From the DHCP pool network
range and deployment, user may know
a priori of the
VLAN or range of VLANs from which OFFERs are sent by DHCP server. Hence it is
recommended to modify fallback VLAN configuration from default to a reasonable
If DHCP server is on VLAN 400 and it's connecting port type is
tagged, following configuration change during initial Cisco ME1200 NID
configuration will cause DHCP OFFERs on VLAN 400 to be processed when ZTP is
triggered in standalone mode.
ztp fallback vlan 400 frame-type tagged interface Gi 1/1-6
If DHCP server is directly connected to one of the interfaces
(say, interface 5), this configuration can be modified further as:
ztp fallback vlan 400 frame-type tagged interface Gi 1/5
If DHCP server is on
VLAN 100 and it's connecting port type is untagged, following configuration
change during initial Cisco ME1200 NID configuration causes DHCP OFFERs on VLAN
100 to be processed when ZTP is triggered in standalone mode.
ztp fallback vlan 100 frame-type untagged interface Gi 1/1-6
If user wishes to
disable fallback VLAN configuration, following command can be configured.
Only a single VLAN
can be configured if port-type is untagged.
no ztp fallback vlan
Once configuration is
modified for above steps, user can copy running-config to startup-config prior
to ZTP reset. This will cause modified fallback configuration to be present
when ZTP process is restarted.