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Cabrillo College

CCNP Semester 5CCNP Semester 5

Building Scalable Cisco NetworksBuilding Scalable Cisco NetworksRick Graziani, Instructor with Mark McGregor

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Scalable Networks Scalability: The ability to grow and adapt

without major redesign or reinstallation More often than not, poor design prevents a

network from scaling gracefully, not outdated protocols or underpowered devices.

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Three-Layer Design Model

Conceptual only There will be

contradictions and some devices may be argued as one type of device or another.

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Sample

3-layer

hierarchy

Layered models can be difficult to comprehend. Exact composition can vary from network to network.In ternet

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The Core Layer

Core Layer: provide an optimized and reliable transport structure by forwarding traffic at very high speeds.

Core routers switch packets – fast. – No ACLs, no redistribution, no fancy packet

manipulation.

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The Distribution Layer

Distribution Layer : provides boundary definition by using access-lists and other filters to limit what gets into the core. Thus, this layer defines policy for the network.

Distribution routers apply routing policies using ACLs, route maps, distribute lists and redistribution.

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The Access Layer

Access Layer : feeds traffic into the network. End users access the network via the access layer.

Access Layer routers employ ACLs designed to prevent unauthorized users from gaining entry and give remote sites access to the network via Frame Relay, ISDN, or leased lines.

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Defining the Router’s Role in a Hierarchy

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An access router2600, 2500, 1700, and 1600 Series

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An access router

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A distribution router3600, 4500, and 4000 series

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A core router

12000, 7500, 7200, and 7000 series

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An ISP core router

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Product Lines (know this!)

Core layer– 12000, 7500, 7200, 7000

Distribution layer– 3600, 4500, 4000

Access layer– 2600, 2500, 1700, 1600

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Key characteristics of a scalable network

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Reliable and Available 24x7 Failures need to be isolated and recovery

invisible to the user Uses scalable routing protocols (OSPF,

EIGRP)– Reachability: Uses complex metrics instead of hop

count– Fast convergence time: How they update other

routers with new information– Congestion control: Less traffic overhead,

incremental updates and route summarization

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Reliable and Available Alternate paths

– Core layer: redundancy– Remote sites with mission critical data: redundant

links Tunnels

– Allow for non-IP layer-3 packets (IPX) to be encapsulated in IP packets

– Allows for IP only policies and routing– Other functions as well

Dial Backup– ISDN, POTS

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Reliable and Available Load balancing (See Tech Note - McGregor)

– Distribute traffic across multiple links to the same destination

– Equal-cost-load-balancing: Same cost/metric– Unequal-cost-load-balancing: Different cost/metric– Per-packet load balancing (process-switching)

• Router alternates paths on a per-packet basis• Allows for more proportional load balancing than per-

destination load balancing• Requires more CPU processing

– Per-destination load balancing (fast switching)• The first packet’s destination address is cached, so all packets

destined for the same address will take the same path

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Making the Network Responsive Routers can prioritize traffic based on

protocol information such as TCP port numbers.

Priority may be important on routers that maintain slow WAN connections.

First come, first served transmission may cause unacceptable responsiveness for delay-sensitive traffic as the router must empty its buffer of another user’s file upload of a long train of packets.

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Making the Network Responsive Cisco addresses priority and responsiveness

through queuing, the process the router uses to schedule packets for transmission. (Sem 6)

Queuing: FIFO, Priority, Custom, WFQ FIFO Queuing (First-In First-Out) - Sem 6

– Prioritizes packets in the order which they arrived– Fastest of the four methods– Cisco default on all interfaces faster than E1

(2.048 Mbps)

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Making the Network Responsive Priority Queuing - Sem 6

– Highest priority traffic gets dispatched before any other packets

– Assign traffic to one of four output queues: high, medium, normal, or low

– Router will check high queue first. When high queue is empty, the router checks medium queue, etc.

– Disadvantage: A lower priority queue may never get serviced or with an acceptable time frame if a higher priority queue is always being serviced

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Making the Network Responsive Custom Queuing - Sem 6

– Allows for up to 16 queues– Solves problem of Priority Queuing– Administrator reserves a minimum amount of

bandwidth for each queue– Higher priority traffic can be put in a queue that

receives more bandwidth– Each queue is serviced sequentially until the

number of bytes transmitted exceeds the configured bandwidth for that queue

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Making the Network Responsive WFQ (Weighted Fair Queuing) - Sem 6

– Priority and Custom Queuing required administrator to predefine priorities and configure access lists

– WFQ uses a complex algorithm to automatically allocate bandwidth to all types of network traffic, but prioritizes delay-sensitive packets so that high-volume conversations don’t consume all the available bandwidth.

– WFQ breaks up large trains of packets so that low-volume conversations don’t get overrun by large file transfers of any other heavy traffic.

– Cisco default on all interfaces E1 (2.048 Mbps) and slower.

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Making the Network Efficient Access Lists - Sem 5 Snapshot Routing - Sem 6 Compression - Sem 6 Dial-on-Demand Routing - Sem 6 Route Summarization - Sem 5 Incremental Updates - Sem 5

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Making the Network Efficient Access Lists - Sem 5

– Prevents (permit or deny) unnecessary, undesirable or unauthorized traffic

Snapshot Routing - Sem 6– Cisco IOS feature that allows distance-vector

routers to exchange their complete tables during initial connection, and then only during active periods.

– Router takes snapshot of table during quiet periods (dialup link is down) and then exchange tables only during active periods (dialup link is up) when interesting traffic brings up the link.

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Making the Network Efficient Dial-on-Demand Routing (DDR) - Sem 6

– Router waits for interesting traffic before activating the link, commonly used with ISDN.

Route Summarization - Sem 5– Route aggregation or route summarization– Number of entries in the routing table can be

reduced if the router uses one network address and mask to represent multiple networks or subnetworks.

Incremental Updates - Sem 5– Routing protocols (OSPF, EIGRP) send routing

updates that contain information only about routes that have been changed and only when there is a change.

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Making the Network Adaptable Coexistence of multiple routed (IP, IPX) and

routing protocols (RIP, OSPF). Route Redistribution

– Allows routing information to be shared (redistributed) among two or more different routing protocols.

– Ex: RIP routes into OSFP area

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Making the Network Accessible but Secure Allows users to connect easily over a wide

variety of technologies, if necessary. Dialup and Dedicated Access - Sem 6

– T1/E1, PSTN, ISDN, etc. Switched Access - Sem 6

– Frame Relay, X.25, ATM, etc. Secure

– PAP, CHAP, TACACS+, RADIUS, etc.

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Coming up!

IP Addressing: VLSM, CIDR

Routing Overview OSPF: Single Area

and Multiarea EIGRP Route Optimization BGP “Security”

Labs!