BPDU Fields Associated with Root Bridge Selection

This subtopic describes the criteria used to determine which device will be elected as the root. The BID and root ID are both 8-byte fields carried in a BPDU. These values are used to complete the root bridge election process. A switch identifies the root bridge by evaluating the Root ID field in the BPDUs it receives. The unique BID of the root bridge will be carried in the Root ID field of the BPDUs that are sent by each switch in the tree. When a switch first boots and begins sending BPDUs,...

Enterprise Composite Network Model

To scale the hierarchical model, Cisco introduced the ECNM, which further divides the enterprise network into physical, logical, and functional areas. The ECNM contains functional areas, each of which has its own Building Access, Building Distribution, and Building Core (or Campus Backbone) layers. It is a deterministic network with clearly defined boundaries between modules. The model also has clear demarcation points, so that the designer knows exactly where traffic is located. It increases...

Common Problems with VTP Configuration

- VTP domain and password must match. - Configuration has been overwritten by another VTP device. - Consider making VTP domain smaller. Common Problems with VTP Configuration The table describes some unexpected results that can occur after VTP configuration. The table describes some unexpected results that can occur after VTP configuration. VTP domain name and password must match on a given switch to receive updates from a VTP server. The domain name is case sensitive. VTP version must be...

Allocate IP address spaces in contiguous blocks Allocate one IP subnet per VLAN

Hierarchical network addressing means that IP network numbers are applied to the network segments or VLANs in an orderly fashion that takes into consideration the network as a whole. Blocks of contiguous network addresses are reserved for, and configured on, devices in a specific area of the network. Here are some benefits of hierarchical addressing. Ease of management and troubleshooting Hierarchical addressing groups network addresses contiguously. Network management and troubleshooting are...

And Advance Your Career Cisco Certified Network Professional CCNP

Recommended Training Through Cisco Learning Partners Building Scalable Cisco Internetworks Building Cisco Multilayer Switched Networks Implementing Secure Converged Wide Area Networks You are encouraged to join the Cisco Certification Community, a discussion forum open to anyone holding a valid Cisco Career Certification (such as Cisco CCIE , CCNA , CCDA , CCNP , CCDP , CCIP , CCSP , or CCVP ). It provides a gathering place for Cisco-certified professionals to share questions, suggestions, and...

Describing Transparent Bridges

This topic describes transparent bridges. A switch has the same characteristics as a transparent bridge. Because switches have replaced bridges as the network device for implementing transparent bridging in modern networks, the basic functionality of a switch is identical to that of a transparent bridge on a per-VLAN basis. To understand STP, it is important first to look at the behavior of a transparent bridge without spanning tree. By definition, a transparent bridge has these characteristics...

Rstp Bpdu Flag Byte

Topology Change ACK Agreement Forwarding Learning f 00 Unknown _ 01 Alternative Backup 10 Root RSTP (802.1w) uses type 2, version 2 BPDUs, so an RSTP bridge can communicate with 802.1D on any shared link or with any switch running 802.1D. RSTP sends BPDUs and populates the flag byte in a slightly different manner than the manner used by 802.1D. An RSTP bridge sends a BPDU with its current information every hellotime period (2 seconds by default), even if it does not receive any BPDUs from the...

RSTP Link Types

Link type provides a categorization for each port participating in RSTP. The link type can predetermine the active role that the port plays as it stands by for immediate transition to a forwarding state, if certain parameters are met. These parameters are different for edge ports and nonedge ports. Nonedge ports are categorized into two link types. Link type is automatically determined but can be overwritten with an explicit port configuration. 2006 Cisco Systems, Inc. Implementing Spanning...

Explaining Trunk Link Problems

Trunks can be configured statically or autonegotiated with DTP. For trunking to be autonegotiated, the switches must be in the same VTP domain. Some trunk configuration combinations will successfully configure a trunk, some will not. Will any of the above combinations result in an operational trunk These elements determine whether or not an operational trunk link is formed and also determine the type of trunk the link becomes the trunking mode, the trunk encapsulation type, the VLAN Trunk...

Adjacency Information

Switch show adjacency gigabitethernet 9 5 detail Protocol Interface Address 06(11) 504 packets, 6110 bytes 00605C865B82 000164F83FA50800 ARP 03 49 31 Switch show adjacency type mod port port-channel number detail internal summary Each time an adjacency entry is created, a Layer 2 data link layer header for that adjacent node is precomputed and stored in the adjacency table. This information is subsequently used for encapsulation during CEF switching of packets. Output from the command show...

Are CEF tables complete and accurate

CEF is the fastest means of switching Layer 3 packets in hardware. The CEF tables stored in hardware are populated from information that is gathered by the route processor. Troubleshooting CEF operations therefore has two primary steps. Ensure that the normal Layer 3 operations on the route processor are functioning properly so that the switch tables will be populated with accurate and complete information. Verify that information from the route processor has properly populated the FIB and...