Link-state routing protocols, such as Open Shortest Path First (OSPF)[] and Intermediate System-to-Intermediate System (IS-IS)[], utilize a replicated distributed database model and are considered to be more-complex routing protocols. Link-state protocols work on the basis that routers exchange information elements, called link states, which carry information about links and nodes in the routing domain. This means that routers running link-state protocols do not exchange rout..
Requesting, Getting, and Acknowledging LSAs
Once all LSA headers have been exchanged using DD packets, each neighboring router has a list of LSAs known by the neighbor. Using that knowledge, a router needs to request a full copy of each LSA that is missing from its LSDB. To know if a neighbor has a more recent copy of a particular LSA, a router looks at the sequence number of the LSA in its LSDB and compares it to the sequence number of that same LSA learned from the DD packet. Each LSA’s sequence number is increment..
BGP Configuration Stencil for Large Networks
The following basic configuration summarizes the commentary of this section. It is not necessary to include the complete configuration as part of your default BGP configuration. You should study this section to see what is suitable for your environment: interface loopback 0 ip address 1.0.0.1 255.255.255.255 router bgp 100 no synchronization bgp router-id 1.0.0.1 no bgp fast-external-fallover bgp log-neighbor-changes ..
Four-Step STP Decision Sequence
When creating a loop-free logical topology, Spanning Tree always uses the same four-step decision sequence: • Lowest Root BID • Lowest Path Cost to Root Bridge • Lowest Sender BID • Lowest Port ID Bridges pass Spanning Tree information between themselves using special frames known as bridge protocol data units (BPDUs). A bridge uses this four-step decision sequence to save a copy of the best BPD..
UplinkFast: Access-Layer Uplinks
Consider an access-layer switch that has redundant uplink connections to two distribution- layer switches. Normally, one uplink would be in the Forwarding state and the other would be in the Blocking state. If the primary uplink went down, up to 50 seconds could elapse before the redundant uplink could be used. The UplinkFast feature on Catalyst switches enables leaf-node switches or switches at the ends of the spanning-tree branches to have a functioning root port whil..
