Network Design Principles

# Network Design Principles

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# Network Design Principles
## Carrier grade
### IP Address Management

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## Content

* Dynamic Routing Protocols

* BGP

* OSPF

* Logical Network Design

* Switched

* Statically Routed

* Dynamically Routed

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* Why?

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* Handle failover

* Discover remote networks

* Choose the best path to the destination

* Lower configuration costs

* Lower failure points?

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![Right-aligned image](igp_egp.svg)

* IGP = Interior Gateway Protocol

* EGP = Exterior Gateway Protocol

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* Border Gateway Protocol

* Distance Vector Routing Protocol

* EGP

* Aggregates all vectors to the most simple one

* Pushes updates based on events

* Only talks to direct peers

* Prevents routing loops by checking the AS-Path

* Announces the configured routing table
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Distance Vector Routing

![Right-aligned image](distance-vector-simple.svg)

Element | Vector
    ------- | ----------------------------
    AS24940 | AS3320
    AS24940 | AS3320 -> AS20773 -> AS13335
    AS24940 | AS3320 -> AS20773 -> AS1299
    AS24940 | AS1299
    AS24940 | AS1299 -> AS13335
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![Right-aligned image](distance-vector-real-ipv4.png)

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![Right-aligned image](distance-vector-real-ipv6.png)

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Route Selection

* Ignores Link-State

* Ignores Hop Count

* Honors AS-Path

* Honors propritary values
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* Open Shortest Path First

* Link-state routing protocol

* IGP

* Interval based
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Link-state routing

* Every router in an AS talks to every other

* Uses SPF to create a tree

* Periodically sends a flood

* Causes a huge amount of traffic

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![Right-aligned image](switched_1.svg)

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![Right-aligned image](switched_2.svg)

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![Right-aligned image](switched_3.svg)

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![Right-aligned image](switched_4.svg)

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* Many SPOF, unable to mesh

* would create loops

* CAM table size is limited

* Content Addressable Memory = MAC table

* All switches hold up all MAC addresses in the same Layer2/VLAN

* limit is around ~512-4096 addresses per device

* Juniper EX2200-48T: 16.000 entries, 864€

* Juniper EX3200-48T (EOL): 32.000 entries, 1975€

* TP-Link T3700G-28TQ: 32.000 entries, 1698€

* Netgear GS724Tv4: 16.000 entries, 150€
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![Right-aligned image](routed_1.svg)

* One Subnet for each switch

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* Static routes configured on all switches

* Works fine on Layer 2 until there are VLANs across routers

* CAM tables will again be too big

* Requires manual configuration for routes

* Redundant ring

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* Less stuff to configure by hand

* Better failover for new links

* TOR switch for hypervisors is still a bottleneck

* We could use OSPF or RIP

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![Right-aligned image](scaling.jpg)

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![Right-aligned image](routed_2.svg)

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![Right-aligned image](cisco-leaf-spine.png)

* 16 Racks

* 16 Switches

* 8 Routers

* 16*40 = 640 Servers

* 640 * 100 = 64.000 Virtual Machines
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* Impossible to have 64.000 Virtual Machines + Hypervisors in the same Layer 2

* Would require switches with 64,000 MAC entries

* Juniper EX92008, 8RU, ~45.000€, per rack

* Dynamic routing protocols route prefixes to a next hop

* Normally used to route nets to a router

* You can route to any IP address?
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![Right-aligned image](wat.jpg)

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BGP as IGP

* Bad: Every router would talk to every other router (fully meshed)

* Fine for small networks, doesn't work in this size

* Each hypervisor will act as a router

* Bad: Needs something to get the routing table

* "Announces the configured routing table" - Slide 7

* Nice: Simple Table of: Sourcenet -> Next Hop

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BGP route reflector

![Right-aligned image](routed_3.svg)

* Everybody sends updates to a central router

* Router pushes updates to all routers that need this information

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* Dynamic routing is fun

* OSPF is fine for announcing hypervisor networks

* BGP is perfect for cloud

* Don't trust vendors for CAM table size