CCNP Switching Exam Notes: Server Load Balancing, Express Forwarding, And Etherchannel.
46.0 Server Load Balancing (SLB) uses the following methods for load balancing traffic:
1. Weighted round-robin: Each physical server is assigned a weight. For a weight n, a server is assigned n new connections before SLB moves on to the next server.
2. Weighted leat connections: Here the SLB assigns new connections to the physical server that has the least number of weighted active connections. If the weight of a physical server is m, then its capacity for active connections is m divided by the sum of all server weights. New connections are assigned to the server with least load.
47.0 The enable a switch port for layer 2 functionality use the following commands:
1. switch(config)# interface <type> <mod>/<num>
2. switch(config-if)# switchport
The first command enters interface configuration mode for the switch interface <mod>/<num>, and the second command enables layer 2 functionality on the port.
Use the "no" form of the switchport command to enable layer3 functionality.
48.0 When CEF (Cisco Express Forwarding) is enabled on a switch, an FIB (Forwarding Information Base) is build that enables forwarding of arriving packets at wire speed. However, there are packets that may still need intervention by Layer 3 Engine. If an arriving packet is required to be forwarded to Layer 3 Engine, then the packet is marked as "CEF punt" and sent to Layer 3 engine for further processing.
49.0 The following are the occasions when the packet is marked as CEP punt and forwarded to Layer 3 engine:
1. An entry can not be found in the FIB
2. The FIB is full
3. The IP TTL has expired
4. The MTU is exceeded, and the packet needs to be fragmented.
5. The encapsulation type is not supported
6. Compression or encryption operation is needed etc.
A switch configured for CEF, uses adjacency tables to prepend Layer 2 addressing information. Nodes in the network are said to be adjacent if they are within a single hop from each other. The adjacency table maintains Layer 2 next-hop addresses for all FIB entries. The adjacency table information is build from the ARP table.
50.0 The EtherChannel also provides link redundancy. If one of the bundled links fail, the traffic through the failed link is distributed to other working links in the channel. The failover is transparent to the end user. Similarly traffic again flows through the restored link, as and when a link is restored.
Switch(config)# port-channel load-balance src-ip
Will configure load balancing on EtherChannel switch links using source IP address.
Note that the load balancing can be done based on source IP, destination IP, both source and destination IP (XOR), source and destination MAC addresses or TCP/UDP port numbers.
Switch# show etherchannel summary
Shows each port in the channel along with the status flag.