SWITCH - THEORY

Cisco Hierarchical Design Model

3Model:

Access

Distribution

Core

Access: Provides end user access to the network LAN. Local devices such as phone, computer and local network.

Distribution:Combination of L2 and L3 switching. Redundant distribution layer switches provides dual path to the access switches and core switches.Providing Routing policy /route selection/ filtering /summarization /security policy.

Core:Backbone provide high speed l3 path between distribution layer and other network segment. Gigabyte /fast Ethernet connectivity. Data / voice / Convergence LAN, WAN, MAN. Reliability and Scalability. Fast switching for traffic into and out of data center.

Depends upon traffic flow.

Note:

Access Model:

User access port typically fast Ethernet or fast. Access switches must have the necessary port density and can be either L2 or L3 Switch.

Distribution Model:

Port from user Access to Distribution layer should be gigabit Ethernet or better.

Distribution switch should be multilayer or L3 switch.

Core Model:

Link from Distribution to Core Gigabit Ethernet channel or 10 Gigabit Ethernet.

VLAN- Virtual LAN

Breaking large network into smaller pieces.

Benefit:

Minimize the amount of broadcast traffic on logical segment. Logical LAN. Logical Subnet. It defines Broadcast Domain. Logical subnet is a group of switch port assigned to the same VLAN.VLAN Members can assign either statically by port or dynamically by Mac Address or username.

Two type of VLAN

End to End –Vlan Members reside on different switches throughout the network.

Troubleshoot more complex because so may switches can carry traffic for specific VLAN and Broadcast can travels many switches.

Local VLAN Based on their location. More scalable and easy troubleshoot. Traffic flow more deterministic. It enables more redundancy and minimize failure domain.

It requires routing function to share resource between VLAN.

Vlan planning

Vlan numbering, name and ip address Vlan placement local or multiple switches

Are any trunk necessary and where? VTP parameters. Test and verification

VLAN Trunk

Trunk is a link that carries traffic for more then one VLAN.

Trunks multiplex traffic from multiple VLAN.

Typically connected switches and enable ports on multiple switches to be assigned to the same VLAN.

Trunk link need a cross cable

Allow same vlan to access from different switch

Switch from reach trunk, trunk will add tag and pass to other switch

Trunk protocol ISL and IEEE 802.1Q (dot 1 q)

ISL

Cisco proprietary

Frame reach the trunk frame will be encapsulation

Tail and header will add here

Don’t recognize the native VLAN.

Native Vlan also adding tail and header

IEEE 802.1Q (dot 1 q)

Industry standards

Header only added

Recognize the Native VLAN not adding any tag.

Native Vlan default VLAN and VLAN1 all are same

When a frame comes into a switch port, the frame is tagged internally within the switch with the vlan number of port. When it reaches the outgoing port the internal tag is removed. If the exit port is a trunk port its vlan is identified in either the ISL or 802.1q tag. The Switch on the other end of the trunk removes the ISL or 802.1q information check the Vlan of the frame and adds the internal tag. If the exit port is a user port, the original frame is send out unchanged, making the use of Vlan transparent to the user.

VTP: VLAN Trunk Protocol

VTP Cisco Property protocol runs over trunk links and synchronizes the VLAN databases of all switches in the VTP Domain.

VTP Domain is an administrative group. All the switches with the group must have the same VTP domain name configured or they do not synchronize databases.

VTP works

Using the configuration Revision numbers and VTP advertisements

All switches send out VTP advertisements every five minutesor when there is a change to the vlan database (When a VLAN is created deleted or renamed)

VTP advertisements contain a configuration Revision Number. This number is increased by one for every Vlan chage.

When switch receives a VTP advertisement, it compares the configuration Revision number against the one in its VLAN database

If the new number is higher, the switch overwrites its database with the new VLAN information and forwards the information to its neighbor switches.

If same number switch ignores the advertisement.New number is lower the switch replies with the more up to date information contained in its own database.

VTP Switch Role

VTP Server: default VTP role. Server can create delete and rename. VTP advertisements and synchronize their databases with other switches in the domain

Client: Clients cannot make VLAN changes. VTP Advertisements and Sychronize their database with other switches in the domain.

Transparent: it can create delete and rename VLANs. But its Vlan’s are only local.

Adding New Switch to a VTP domain

Disconnect from network Change to VTP transparent and delete the VLAN.dat file from its flash memory. Set to fake vtp domain name and into client mode. Reboot. Configure corrects vtp setting such as domain password mode and version. Connect the switch to the network & verify that its receives the correct information.

Issue

VLAN

Physical connectivity

Correct VLAN Configuration

Allowed VLAN.

Trunk Problem:

Both side link trunk modes, check both side configure with same encapsulation,

Vtp:

Domain name matches of both switches (Case Sensitive)

Check revision number. Password, switches in transparent mode.

HSRP

Hot Standby router protocol (HSRP) is a Cisco property.

Two or more device support a virtual router with a made up Mac Address and unique ip address

Host use this ip address as their default gateway and the Mac address for the layer 2 header.

Virtual Mac address is 0000.0c07.ACxx. In which XX is HSRRP group.

Multi group (Virtual router) are allowed.

Active routers forwards traffic.

Standby is backup.

Standby routers send hellos (Multicast 224.0.0.2 Udp port 1985 to detect a failure of the active router. On failure the sandby device starts answering messages send to the ip and Mac addresses of virtual router.

Active router is chosen because it has the highest HSRP priority (Default Priority 100). In case of a tie. The router with the highest configured ip address wins the election.

If you decide particular switch to become active you must change the priority to high.. highest priority router become active

HSRP States:

Initial :HSRP is not running

Learn: the router does not know the virtual ip address and is waiting to hear from the active router.

Listen: the router knows the ip and Mac of the virtual router but it is not the active or standby router.

Speak: Router Sends periodic: Hellos and participates in the election of the active router.

Standby: router monitors hellos from active router and assumes respobsibility if active router fails.

Active: router forwards packets on behalf of the virtual router.

Along with configuring Priority, configure preempt to enable a router to take over if the active router has lower priority.

Hello and hold times caller timer

Hello time can change from sec to msec. Default 3 seconds

Hold time also can change form sec to msec default 10 seconds.

Router in the same HSRP group must belong to the same subnet /VLAN.

Standby  group-no Ip virtual-IP-address

HSRP 1 IP 10.0.0.1

Authentication helps prevent unauthorized routers from seeing user traffic. MD5

Trouble shooting commands

Show standby interface interface

Show standby brief

To monitor

Debug standby

SPANNING TREE PROTOCOL

1. What is the port cost of STP?

Link Speed Cost

10 Mbps 100

100 Mbps 19

1 Gbps 4

10 Gbps 2

What is root Port?

      Switch port is closer to root bridge. (In terms low Cost).  Which port is reaching to the root bridge of the network segment is called root port. Every non root bridge has a single root port.

What Designated Port?

    Every network have single designated port. Closest to the root bridge. All the ports on the root bridge is designated port.

What is Non-designated port?

Non designated ports are block traffic for loop free.(redundant link).