User manual

Publication 1783-UM003D-EN-E - December 2009 41
Chapter 2
You can configure an EtherChannel in one of these modes: Port Aggregation
Protocol (PAgP), Link Aggregation Control Protocol (LACP), or On.
Configure both ends of the EtherChannel in the same mode.
• When you configure one end of an EtherChannel in either PAgP or
LACP mode, the system negotiates with the other end of the channel to
determine which ports should become active. Incompatible ports are
suspended. Instead of a suspended state, the local port is put into an
independent state and continues to carry data traffic as would any other
single link. The port configuration does not change, but the port does
not participate in the EtherChannel.
• When you configure an EtherChannel in the On mode, no negotiations
take place. The switch forces all compatible ports to become active in
the EtherChannel. The other end of the channel (on the other switch)
must also be configured in the On mode; otherwise, packet loss can
occur.
If a link within an EtherChannel fails, traffic previously carried over that failed
link moves to the remaining links within the EtherChannel. If traps are
enabled on the switch, a trap is sent for a failure that identifies the switch, the
EtherChannel, and the failed link. Inbound broadcast and multicast packets on
one link in an EtherChannel are blocked from returning on any other link of
the EtherChannel.
DHCP Persistence
Every device in an IP-based network must have a unique IP address. The
Dynamic Host Configuration Protocol (DHCP) automatically assigns IP
address information from a pool of available addresses to newly connected
devices (DHCP clients) in the network. If a device leaves and then re-joins the
network, the device receives the next available IP address, which might or
might not be the same address that it had before.
The switch can be set to operate as a DHCP server to provide DHCP
persistence. With DHCP persistence, you can assign a specific IP address to
each port, ensuring that the device attached to a given port will get the same IP
address.
IMPORTANT
To make sure DHCP persistence works correctly, follow the
application rules. Refer to Configure DHCP Persistence on page
76.