Design Review Template - NETS

Hierarchical (MultiLayer) Network Design
By default UDLD is disabled globally, and enabled in readiness on fiber ports. As UDLD is an
infrastructure protocol needed between switches only, it is disabled by default on copper ports as these
tend to be used for host access.
Set udld enable
Set udld enable
! once globally enabled, all FE and
GE fibre ports have UDLD enabled
by default.
! for additional specific ports and
copper media if needed.
Set udld aggressive-mode enable ! all point to point links
Enabling UDLD ‘aggressive-mode’ provides additional benefits:
This feature provides enhanced protection against dangerous unidirectional link conditions in the
following situations, and includes attempts to re-establish a connection with the neighbor upon failure
detection:
- One side of a link has a port stuck (either Tx and Rx).
- One side of a link remains up while the other side of the link has gone down. This reduces the
reliance on Layer 1 FEFI mechanisms
- After eight failed retries, the port is transitioned to an ErrDisable state and a syslog message
logged
- In these cases, UDLD aggressive mode will ErrDisable both of the ports on the link and stops the
black-holing of traffic
Aggressive mode UDLD also allows the possibility to manually configure the UDLD probe/echo
message interval between values ranging from 7-90 seconds, the default interval being 15 seconds.
EtherChannel (PAgP)
EtherChannel technologies allow the inverse multiplexing of multiple (up to eight on Cat6k) channels into
a single logical link, and although each platform differs from the next in implementation, it is important to
understand the common requirement
- An algorithm to statistically multiplex frames over multiple channels
- Creation of a logical port so that a single instance of STP can be run An algorithm to statistically
multiplex frames over multiple channels
- A channel management protocol. PAgP is a management protocol that will check for parameter
consistency at either end of the link, and assist the channel in adapting to link failure or addition
- PAgP requires that all ports in the channel belong to the same VLAN or are configured as trunk
ports. (Because dynamic VLANs can force the change of a port into a different VLAN, they are
not included in EtherChannel participation.)
- When a bundle already exists and a VLAN of a port is modified, all ports in the bundle are
modified to match that VLAN
- PAgP does not group ports that operate at different speeds or port duplex. If speed and duplex are
changed when a bundle exists, PAgP changes the port speed and duplex for all ports in the bundle
Configuration Options: EtherChannels can be configured in different modes, summarized in the table
below:
Mode
On
Configurable Options:
PAgP not in operation. The port is channeling regardless of how the
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