Blue Print Topics Covered This Post
1.00 Implement Layer 2 Technologies
1.20 Implement VLAN and VLAN Trunking Protocol (VTP)
(a) VTP
(b) Pruning
(c) Bridging – Transparent, IRB, CRB
VTP
VLAN Trunking Protocol (VTP) is used to propogate VLAN configuration information across a VTP Domain, simplifying the administration of adding and deleting VLANs without having to touch every element. For switches that support VTP, VTP information is propogated across ISL or 802.1q Trunks interfaces.
Devices in a VTP domain can either be a Server, client or transparent. Only a server can be used to administratively create or delete VLANs (multiple servers are permitted in a domain, config changes on one server will be propogated and processed on the other servers). A client will take action on the VTP messages, creating or deleting VLAN information. A VTP transparent switch ignores VTP information. All VTP types propogate VTP information within the VTP domain.
| Function | Server | client | Transparent |
| Originates VTP messages | Yes | No | No |
| Processes received VTP messages | Yes | Yes | No |
| Forwards received VTP messages | Yes | Yes | Yes |
| Saves the VLAN configuration in flash:vlan.dat or nvram | Yes | Yes | Yes |
| Can use config mode to add/delete VLANs | Yes | No | Yes |
All switches have a default configuration mode as a VTP server and belong to the NULL VTP domain. The VTP database besides the domain has a configuration version associated with it (starting at 0 and incrementing for each VLAN configuration changes) any switch that recieves a VTP database update that has a higher configuration version than what is currently used will immediately overwrite the existing database with the new configuration version. Joining of several operational switches together with a default VTP configuration can cause unexpected consequences where some VLAN information could be lost.
VLAN types and interaction with VTP
| VLAN | Normal or Extended VLAN? | Works with VTP v1/v2? | Comments |
| 0 | Reserved | N/A | Not available for use |
| 1 | Normal | No | Default VLAN |
| 2 - 1001 | Normal | Yes | |
| 1002 - 1005 | Normal | No | FDDI and Token Ring Translational VLANs |
| 1006 - 4094 | Extended | No | can be used with VTPv3 |
VLAN Database Storage and Configuration
| VTP Server | VTP Transparent | |
| Storage of Normal Range VLANs | flash:vlan.dat | flash:vlan.dat (preference) or running config |
| Storage of Extended Range VLANs | Not Permitted | running config |
| CLI configuration of Normal Range VLANs | vlan database or conf t | vlan database or conf t |
| CLI configuration of Extended Range VLANs | Not Permitted | conf t |
VTP Pruning
VTP Pruning is a mechanism to reduce the flooding scope of Broadcast, Unknown and Multicast frames traffic across VLAN trunks. If a particular switch does not locally support a particular VLAN, VTP can "prune" it so that traffic related to that VLAN does not get sent across the trunk from a peer switch.
A VTP password can be defined to mitigate an uncontrolled device cannot effect the VTP domain (unfortunately it does not appear possible to stop VTP from exiting a trunk interface, however MAC filtering can be used to stop unwelcome VTP traffic from entering your switch)
Transparent Bridging
This stuff wasnt covered in the Certification Guide, so I used Cisco LAN Switching maybe this is more of a lab than written topic but anyway...
Routers can be configured not to route "no ip routing" and the establishment of bridge groups can be used to link physical interfaces (or their subinterfaces) that have individual broadcast domains into a single broadcast domain using the concept of bridge groups and using STP to ensure loop free operation.
Concurrent Routing and Bridging (CRB) was the initial step to support the simultaneous operation of bridging between some interfaces, while also performing routing, however without introducing a physical loopback to join a bridge group to a routed port it was not possible to combine routing and bridging within a single service.
Integrated Routing and Bridging (IRB) introduces the concept of a bridged virtual interface (BVI) which is a layer 3 interface that represents the bridge group (a Virtual MAC address for the BVI is created) and provides the capability for the Bridge Group traffic to be routed to other layer 3 interfaces on the router
No comments:
Post a Comment