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What are some of the way to address broadcast issue in traditional networks?
- The two major problems with traditional networks have always
- been availability and performance. These two problems are both impacted
- by the amount of bandwidth available.
- To improve network
- performance it is important to reduce the number of broadcasts, because lot of
- broadcast on a network causes downtime which can lead to failure. The more
- broadcast domains you have the better and the smaller they are the better.
- Introduce VLANS into your network, a network without VLAN means a big
- broadcast. Sub netting is also another factor that helps increase performance
- on a network.
What is a 20/80 Rule and explain diagram?
- In today's networks, traffic patterns are moving toward the 20/80
- model. In the 20/80 model, only 20 percent of traffic remains local to the workgroup
- LAN, and 80 percent of the traffic leaves the local network.
What are the key requirements that placed pressure on the emerging campus designs or what are the recommendations by CISCO for campus design?
- Fast Convergence: To adapt very quickly to changes in the network topology, for example if a subnet goes down we expect the router or routing protocol that is implemented in that network to trigger very quickly updates to this network. EIGRP and OSPF are example of protocols that help propagate updates for fast converge, they react quickly to changes. OSPF tends to be quicker for fast convergence than other
To determine the desirability of a given path to a destination for certain applications or user groups. Spanning Tree is an example of a protocol that provides deterministic paths because the STP will go through a number of stages:
- 1 It will not disable links that are not fast, only links that are slower (in doing this your providing paths for communication that are
- much faster)
- Redundancy: To ensure the network is operational at all times. For example aggregation links this adds extra can be used in case one links fails the other link can be reactivated for continue use. HCRSP load balance is other example. Making sure
- providing alternative routes so that the network is functional all the time
- Scability:Able to handle the increased traffic demands. How do you increment scability? Down to many factors such as hardware,
- software, logical design, physical designs. You need to think about the logical
- design first, it doesn’t allow you to scale, in the physical phase you need to
- provide IP addresses in order to scale
- Centralised application: They are available to support most of all users on the
- network. For a centralised application will be in the server farm
- Multi-Protocol support: Able to support multiprotocol environments. To be able to support multimedia environment you need to consider the types of protocol you run on
- your network
Able to support IP multicast traffic e.g IGRP
Focuses on the shift in traditional patterns
What is VLAN and why is it needed?
VLAN takes on switch or one particular network and breaks it down into multiple logical networks. With VLANS you get security boundaries and broadcast separation.
What are the 2 types of VLAN?
End to end VLANs: Each VLAN is distributed geographically throughout the network. Users are grouped into each VLAN regardless of the physical location, which theoretically easing network management. A user moves throughout a campus, the VLAN membership for that user remains the same. Switches are configured for VTP server or client mode.
Local VLANS: Create local VLNAs with physical boundaries in mind rather than job function of the users. Local VLANs exist between the access and distribution layers/Traffic from a local VLAN is routed at the distribution and core levels/Switches are configured in VTP transparent mode/ Spanning tree is used only to prevent inadvertent loops in the wiring closet/One to three VLANs per access layer switch recommended
What are some of the characteristics of OSPF?
OSPF supports only IP routing
OSPF routes have an administrative distance of 110
OSPF uses costs as its metric, which is computed based on the bandwidth of the link
OSPF uses the Dijkstra Shortest Path First algorithm to determine the shortest path.
OSPF is a classless protocol, and thus supports VLSMs
OSPF consists of areas and autonomous system
What are the 3 separate tables that OSPF process builds and maintains?
Neighbor Table: Contains a list of all neighboring routers
Topology Table: Contains a list of all possible routes to all know networks within an area
Routing Table: Contains the best route for each know network
OSPF understand DR and BDR election processes/ How do you determine the DR?
DR and BDR election is accomplished via the Hello protocol. Hello packets are exchanged via IP multicast packets on each segment.
However, only segments that are broadcast and nonbroadcast multi-access networks (examples are Ethernet and Frame Relay) will perform DR and BDR elections. Point-to-point links, like a serial WAN for example, will not have a DR election process.
- On a broadcast or nonbroadcast multi-access network, the router with the highest OSPF priority on a segment will become the DR for that segment. This priority is shown with the show ip ospf interface command.
- The default priority for a router interface is one. If all routers have the
- default priority set, the router with the highest Router ID (RID) will win.
- The RID is determined by the highest IP address on any interface at the moment of OSPF startup. This can be overridden with a loopback (logical) interface. If you set a routers interface to a priority value of zero,
- that router wont participate in the DR or BDR election on that interface. The state of the interface with priority zero will then be DROTHER.
Explain what the cost of the link involves for OSPF: bandwidth delay, latency?
- The shortest path (Lowest cost) is used in building topology and for selecting the best route. Faster links (higher bandwidth) have the
- lower cost. So the lower the cost the better the route
What are the OSPF Router Types?
Routers with all their interfaces within the same area
Routers with at least one interface connected to area 0
Area Border Router:
- ASBR (Autonomous
- System Boundary Router): Routers that have at least one interface connected
- to an external internetwork (another autonomous system)
Routers with interfaces attached to multiple areas
What does PPDIOO stands for and explain each one?
- -Preparation (Gather information), establish
- organizational requirements, developing a network strategy.
- -Plan (Provide recommendation
- technologies and services that will move forward business)
- -Design (Offers design options that
- meets business needs and technical requirements, Some cannot afford redundancy, Recommend Redundancy, Optimal network recommendation)
mplementation (Test network and if can be reached, Implementation in real time)
- (Maintaining network health through day to day operations, including maintaining high availability and reducing expenses)
- (Monitor network, Monitor and optimize, Software such as LMS to monitor
- network, VLANS for optimization, Quality of service e.g. VoIP) proactive management of
- network to identify and resolve issues before they affect the organization. Reactive fault detection and correction (troubleshooting) is needed when proactive management cannot predict and mitigate failures
What is the role of STP and its various forms?
- In large networks topology changes occur frequently, thus high availability is very
- important and necessary by using multiple links between switches in a network,
- if one links fails the other links takes over, this provides redundancy. But
- there is a big issues, redundant links causes storm loops within the network
- this leads to both network bandwidth and resources starvation because broadcast
- frames occur all the time in switched networks.
- To solve the problem with infinite loops or broadcast storms a standardized protocol was created called the Spanning Tree Protocol (STP). The Spanning Tree
- Protocol is an algorithm responsible for identifying active redundant links in
- the network and blocking one of these links, thus preventing possible network
- loops. STP is enabled by default in the switches. All switches generate and
- process data messages called Bridge Protocol Data Units (BPDUs) to identify
- redundant paths by using the Spanning Tree algorithm.
What are the STP switchports states?
Discarding: This state is seen in both a stable active topology and during topology synchronization and changes. The discarding state prevents the forwarding of data frames, thus “breaking” the continuity of a Layer 2 loop.
Learning: This state is seen in both a stable active topology and during topology synchronization and changes. The learning state accepts data frames to populate the MAC table to limit flooding of unknown unicast frames.
Forwarding: This state is seen only in stable active topologies. The forwarding switch portsdetermine the topology. Following a topology change, or during synchronization, theforwarding of data frames occurs only after a proposal and agreement process.
Explain the types of Spanning Tree Enhancements ?
- BPDU guard: Prevents accidental
- connection of switching devices to PortFast-enabled ports. Connecting switches to PortFast-enabled ports can cause
- Layer 2 loops or topology changes.
- BPDU filtering: Restricts the switch from sending unnecessary BPDUs out access
- Root guard: Prevents switches connected on
- ports configured as access ports from
- becoming the root switch.
Prevents root ports and alternate ports from moving to forwarding state when they stop receiving BPDUs.
Explain Root Guard Motivation and Root
- Root Guard Motivation
- Switches A and B comprise the core of the network. Switch A is the root bridge.
- Switch C is an access layer switch. When Switch D is connected to Switch C, it begins
- to participate in STP. If the priority of Switch D is 0 or any value lower than that of the
- current root bridge, Switch D becomes the root bridge.
- Having Switch D as the root causes the Gigabit Ethernet link connecting the two core
- switches to block, thus causing all the data to flow via a 100-Mbps link across the
- access layer. This is obviously a terrible outcome.
- Root Guard OperationAfter the root guard feature is enabled on a port, the switch does not enable that port to become an STP root port
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