Identifying Ip(Class A, B, C,D)

Classes A–D Review
•  Network hosts can be assigned a Class address of Class A–D
•  These are simplt a grouping of addresses that indicate host and address
•  Class A has the network number in the first byte of the address and the last
three bytes are assigned to the host.
•  Class B has the network number in the first two bytes of the address and the
last two bytes are assigned to the host.
•  Class C has the network number in the first three bytes of the address and
the host is assigned to the last byte.
•  Class D is a multicast address.
•  A is the first letter of the alphabet and therefore the network numdber is
assigned the first byte.
•  B is the second letter and therefore has the network number assigned to the
first two byrtes.
•  Class C is the third letter and therefore has thew network number assigned
to the first three bytes.
The classes are
Class A: 0–127
Class B: 128–191
Class C: 192–223
Class D: 223–239
Reserved: 240–254
Private Ip address: –
Addresses: 16,777,216 –
Addresses: 1,048,576 –
Addresses: 65,536


In Class D: – is multicast.



The original: 802.1D spanning-tree
Switches forward brodcast packets out all ports by design
Redundand connections are necessary in buisness networks
The place of the spanning tree: drop tress on redundant links (until they are needed)

Original STP was created to prevent loops
Switches Send “probes” into the network called Bridge Protocol Data Units (BPDUS) to discover loops
The BPDU probes also help elect the core switch of the network called the root bridge
The BPDU’s are multicast
The simlistic view of STP: All switches find the best way to reach the root bridge the block all the redundant links

BPDUS are sent once every two seconds
Priority is some value between 0 to 61440 (Default is 32768); Increments of 4096 -lower is better

Three Port Types:
-Root Port: used to reach the root bridge
-Designated Port: Forwarding port, one per link
-Blocking/Non-DesignatedPort: Where tree fell

(Root bridge never blocks a port)

How STP finds the Best Path:
1) Elect the root
2) Swictches find lowest cost path to root
3) use lower bridge id on equal cost paths
4) Use lower port to break a tie

PVST(Per Vlan Spanning Tree Protocol)
All modern switches run PVST
One Instance of STP per VLAN
One root Bridge elected for each VLAN
Helps LOAD-BALANCE more effectively

The spanning-tree command
#spanning-tree Vlan x root primary
#spanning-tree vlan x root secondary
#spanning-tree vlan x priority <number>

Problems with Spanning Tree:

Listening – 15 sec of listening for BPDUs. Switch sends/recieve BPDUs
Learning – 15 secs of learning Mac Address. Populates switch CAM table
Forwarding – Port is forwarding traffic

(Blocking – Switch will wait upto 20 seconds before moving a blocked port into a listening phase.)

Problems and Solutions:
Problems with PC’s: Modern PC’s can boot faster than 30 seconds

-Solution: PortFast
PortFast disables Spanning tree on the port.

Problem with uplink ports: 50 Seconds of down time casues big problems
– 802.1w
– Proactive system
– Redefined port roles
– Many STP similarites

RSTP Port States:
-Discasrding (STP Blocking)
-Learning (STP Learning)
– Forwarding (STP Forwarding)

RSTP Port Roles:
– Root port (Reaching the root not the root)
– Designated port (All root bridge ports are designated)
– Alternate Port (Rememers a blocked port instead of forgetting as in STP)
– Edge Port (conncts to non switch devices similar to portfast)

Why RSTP is better:
1) Does not forget the ports.
2) Proactive nature many of the safety timers of STP are eliminated e.g. bonus,learning
3) Any change to trunk ports flood through the network to other switches

Redundancy Protocols(HSRP,VRRP,GLBP)

Redundancy Protocols:

Created By cisco
Uses a default Hello timer of 3 seconds with a hold timer of 10 seconds

Gateway oraganized into standby groups
One gateway Active, others in standby state
Phantom (virtual) router Ip and mac address generated
Hello Message sent once evert 3 seconds; dead after 10 seconds.

Virtual Mac Address

0000.0C 07.AC XX
Cisco Vnedor Id 00000C
XX- Group id

1) Create a standby group
2) Reassign Ip adress
3) Verify
4) Optimize and tune

If priority is not set then it would rely on higest ip address to decide on the Active router.

Tuning and Optimizing:
– If intertace goes down it takes off a predecided off the priority. It has to be configured with preemtion
Created by the IETF
Works between multiple vendors
has Faster timers than HSRP by default -Hello of 1 second, HOLD timer of 3 seconds

Active/Standby becomes Master/Backup
Standby group becomes VRRP Group
Master router can share Virtual Ip
One Second hello timer, three times
Hello = Down Time(+ skew timer)

1) Configure VRRP group
2) Otimize setting
3) Verify
Created by cisco
Identical features to HSRP, but allows an active-active connection that adds load-balancing

Single VIP with multiple macs
Active virtual Gateway, Acts as the Point man
Other routers act as Active virtual forwarders