Planning for complex networks

Three level Hierarchical Design Model

• Access layer : Provides network access to the end stations
• Distribution layer: Intermediate devices provide connectivity based on Policies.
• Core layer: Provides a high-speed switched path between distribution elements

Demerits

• Where do wireless devices fit in?
• How should internet access and security be provisioned?
• How do you account for remote access, suc as dial-up or VPN?
• Where should work group and enterprise services be located?

To over come this problems  the newer Cisco model aroused

The Enterprise Composite Model

The enterprise model is broken into three large sections.

• Enterprise Campus     -- Switches that make up a LAN
• Enterprise Edge         --  The portion of the enterprise network connected to the larger world
• Service Provider Edge --  The different public networks that are attached.

The enterprise campus  

        feature

• campus Backbone :  the core of the LAN
• Building Distribution :  connects subnets/ VLANs and applies policy
• Building Access: connects users to network
• Management: An out-of-band network to access and manage the devices
• Edge distribution: a distribution layer out to the WAN
• Server Farm: for enterprise services

The enterprise EDGE

• E-commerce
• Internet connectivity
• Remote access 
• WAN  --  frame relay , PPP   etc

The service provider (ISP)

• Internet service provider(ISP)
• Public switched telephone network (PSTN)
• Frame Relay, ATM, and PPP

SONA  and IIN

IIN -  intelligent information network

    phase I  -  Integrated transport  --   describes a converged network….   Forms  the  path to the destination

   phase II  --  Integrated services  --  attempts to virtualize resources,   --  by this  many services can reside in one device to ease management.      The load balancer    is an example…. It virtualizes several servers   as  one device.

Phase III  -  Integrated application.     --   application oriented network (AON)  --   ISR (integrated service router)  with AON blade will be able to create  AON

SONA  ( services-Oriented Network Architecture)    

   sona makes IIN ideal for enterprise network.   

  SONA   breaks IIN function into three layer

• Network Infrastructure : Hierarchical converged network and attached end systems
• Interactive services: Resources allocated to applications
• Applications: Includes business policy and logic

ROUTING PROTOCOLS

Routing protocols pass information about the structure of the network between routers.  

Cisco routers support multiple routing protocols.

Administrative distance

 when identical routes are learned from two or mote separate sources  the AD  is used to discriminate the path.       Risk-factor    is a descriptive name for the AD value…    the prefix from lower AD value is preferred

AD value can be manually adjusted.

Table  list default values for various routing protocol.

Routing protocol characteristics

• EIGRP  is Cisco proprietary,   simple to configure
• OSPF is open standard ,  bit difficult to implement and support
• BGP is open standard,  used to exchange routes to external routers.  It can b every complex to implement.

Choosing a Route

   how to forward a packet.       They look for a match to the destination ip address.   With the longest match.

10.1.1.1

Routing table has    0.0.0.0      --- matches 0 bit

                                   10.1.0.0  ---- matches 16 bit

                                    10.1.1.0 ---- matches 24 bit              -- longest is preferred.

Planning a routing implementation.

• Cisco lifestyle Services:    uses the PPDIOO   model   (Prepare, Plan , Design, Implement, Operate and Optimize)
• IT Infrastructure Library (ITIL):   give importance to bisiness requirements .
• Fault, configuration, Accounting, Performance, and Security (FCAPS)  -- has five management categories
• Telecommunication Management Network (TMN): based on the FCAPS

EIGRP

Features

• Cisco proprietary
• Distance vector
• Classless routing protocol
• Complex metric based on bandwidth and delay
• Fast convergence
• Support for VLSM
• Partial updates conserve network bandwidth
• Supports load-balancing across unequal-cost paths
• Uses multicast 224.0.0.10  
• Supports authentication
• Manual summarization at any interface

EIGRP uses three table

Neighbor table : neighbors. From hello's

Topology table:  eigrp routing information.  Loop free alternatives

Routing table : best paths from the topology table

EIGRP packet  types

• Hello:  identifies neighbors and keep alive mechanism
• Update: Reliably sends route information
• Query: Requests specific route information
• Reply: response to query
• ACK: acknowledgment

Hellos and ACK  are not acknowledged.

The neighbor is removed after 16 retransmissions (hello).

Neighbor discovery and route exchange

The process of neighbor discovery and route exchange  between two eigrp routes  is as follows

Step1. router A sends out a hello

Step2: router B sends back a hello and an update.  The update contains routing information

Step3:  router A acknowledges the update

Step4:Router A sends its update

Step5: Router B acknowledges

When two routers are EIGRP neighbors, they use hellos between them as keepalives. Additional route information is sent only if a route is lost or a new route is discovered. A  neighbor is considered lost if no hello is received within three hello periods( called the hold time) .  The default hello/hold timers

• 5/15 seconds   for multipoint circuits with bandwidth greater than T1 and for point-to-point media
• 60/180 seconds for multipoint circuits with bandwidth less than or equal to T1

Debug ip eigrp packets

Debug ip eigrp

Show ip eigrp neighbors

Eigrp route selection

An eigrp router receives advertisements from each neighbor listing athe advertised distance (AD) and feasible distanc e(FD) to a route. The AD is the metric from the neighbor  to the network. FD is the metric from this router, through the neighbor, to the destination network.

Eigrp metric

Metric=256{kl*(10^7/Bwmin)} +{(k2*Bwmin)/(256-load)}+k3*∑delays{k5/reliability+k4}

The k values are constants. Their default values are k1=-1, k2=0, k3=1, k4=0,  and k5=0  . If K5 =0, the final part of the equation (k5/[rel+k4]) is ignored.

Bwmin is the minimum bandwidth along the path-- the choke point band width.

Delay values are associated with each interface. The sum  of the delays (in tens of microseconds) is used in the equation.  Taking the default k values into account, the equation simplifies to the  one shown.

Metric = 256{(10^7/Bwmin) +∑delays}

Uses DUAL algorithm..  (diffusing update algorithm)

Dual is the algorithm use by eigrp to choose best paths by looking at AD and FD.  The path with the lowest metric is called the successor path.  Eigrp paths with AD than the FD of the successor path are guaranteed  loop-free and called feasible successors.

Successor -  with lowest metric
Feasible successor  - next path if the successor fails.

After the router has chosen a path to a network, it is passive for that route. If a successor path is lost and no feasible successor is identified, the router sends out queries on all interfaces in an attempt to identify an alternate path. It is active for that route. No successor can bechosen until the router receives a reply to all queries. If a reply is missing for 3 minutes, the router becomes in stuck in active (SIA). In that case , it resets the neighbor relationship  with the neighbor that did not reply.

Stuck in Active  -   if the neighbor does not respond to the 3 queries.. 

Three common causes for  SIA

• CPU or memory usage is so high on the neighbor that  it cannot process the query or reply.
• The link between the routers drops packets. Enough packets get through to maintain the neighbor relationship,  but some queries or replies are dropped.
• Unidirectional link, so the router never receives packets from its neighbor.

Configuration 

Router eigrp <AS>

Network <network> <wild card mask>

Creating an EIGRP default route

(config )# ip default-network 10.0.0.0

Verification commands

#show ip eigrp topology

#show ip eigrp neighbors

Customizing the eigrp configuration

Passive interface   <int>     -   update will not be sent through that interface

Passive interface  default   - update will not be sent through any interface

     here the neighborship has to be enabled  manually using the neighbor command.

We can use no passsive-interface  interface for the ones that should run the protocol,

Config)#router eigrp 7

Config-router)#passive-interface default

Config-roiuter)# no passive-interface s 0/0/0    ---

Unicast neighbor

Eigrp usually uses a multicast to ip address 224.0.0.10 for its messages.

We can configure it to use a unicast address instead with the routing protocol configuration command neighbor ip address.

Summarization

Eigrp defaults to automatically summarizing at classful network  boundaries.

Router (config-router)#  no auto-summary

Load Balancing

Capable of load balancing over unequal metric paths..

Variance   --- command used to configure load balancing over up to six loop-free paths with a metric lower than the product of the variance and the best metric..

   100   variance 2    then    all the path with matric less than 200 will be part in the load balancing.