�Case for Task-Driven Network-Wide Abstraction approach to Enterprise Design

Yu-Wei (Eric) Sung

Internet Systems Lab

Dept of ECE, Purdue University

(with Prashant Garimella, Sunil Krothapalli, and Sanjay Rao)

LISA 2007 Configuration Workshop�Nov 12, 2007, Dallas, TX

Motivation: Task-driven Network-wide Abstractions

• Tremendous interest in simplifying enterprise design and configuration using abstractions
• Many prior efforts…
• Template-driven (eg: Presto), BGP Policy specification (eg: RSPL), Vendor-neutral config specification (eg: SNMP MIBS)
• Our proposal: “Task-driven” “Network-wide” abstraction approach to network design
• Task-driven: capture intended requirements, eg: performance, security, manageability
• Network-wide: consider requirement of the network as a whole
• Focus on enterprise & campus networks 🡪 not well understood

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Methodology

• Three-pronged research framework

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• First step: “White-Box” approach to study enterprise networks
• Static analysis of topology and router/switch configurations
• Gain deeper understandings through interaction with operators
• White-box studies are rare
• Significant effort to bootstrap relationships with operators
• Sensitive nature of data: access non-trivial

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Bottom-Up, �White-Box study

Abstraction

Top-Down�Network Design

Case Study: VLAN

• Why study VLAN?
• Widely prevalent in enterprise/campus networks, little understanding in research community
• VLAN Configuration: time-consuming, error-prone
• Critical area for abstraction
• Prevalent @ Purdue University
• 200 routers, 1300 switches, hundreds of VLANs
• First empirical study of VLAN usage �(SIGCOMM INM Workshop 2007)

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What is VLAN?

• A VLAN groups hosts attached to different switches as if they are on the same wire
• Each VLAN belongs to a stand-alone subnet
• Simplifies address assignment, e.g. writing ACLs
• VLAN spans at Purdue University
• 80%: 1-2 buildings; some: entire campus (e.g. classrooms)

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VLAN 1

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.

.

.

VLAN 3

VLAN 2

R1

H2

H3

VLAN 1

VLAN 2

H4

.

.

.

.

S2

S

R2

S3

Access

Trunk

S1

H1

3 key components of VLAN Configuration

1. Access port
2. Trunk port
3. Subnet Config

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VLAN 2

H2

VLAN 1

H1

R1

S

Fa0/1

Fa0/2

S1

Fa0/1

Fa0/2

interface FastEthernet0/1� switchport mode trunk� switchport trunk allowed vlan 1,2

interface FastEthernet0/1� switchport mode access� switchport access vlan 1

interface Vlan1

description subnet 192.168.1.0/24

ip address 192.168.1.1 255.255.255.0

Design Issues

• Communication between hosts from different VLANs must go through a router
• Performance Inefficiencies: Longer delay, harder to debug since data may flow through other buildings
• Placement of designated router: Where to best place the router for hosts in a given VLAN?

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VLAN 1

VLAN 3

VLAN 2

R1

H2

H3

VLAN 1

VLAN 2

H4

.

.

.

.

S2

S

R2

S3

Access

Trunk

S1

H1

Physical

Data

🡨 Building1

Results

• Performance Inefficiencies
• Inefficiency = # hops in data flow path/ # hops in physical path
• Inefficiencies as large as 14, > 4 for about 12 % host pairs
• Placement of designated router
• Sub-optimal placement: a router not placed in the same building as where the majority of hosts in that VLAN are
• More pronounced for wider-spread VLANs: 11%, 33%, and 58% for VLANs that span 1, 2, and >2 buildings
• Typical cause: evolution of network
• See INM’07 paper for complete results and discussions of other issues

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Example: Task-driven VLAN Abstraction and Top-down Network Design

• Abstraction: Complete network topology consists of routers/switches/hosts, a set of hosts in VLAN X

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Suggest a router for VLAN X…

• Task 1: Minimize inefficiencies communicating with all other VLANs
• Task 2: Task 1 + Host H in VLAN X is a major network storage server for the entire network

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Summary & Future Work

• Goal: Task-driven, Network-wide abstraction to enterprise network design
• Three-pronged research framework
• First step: White-box approach to studying networks, providing critical insights for abstraction design
• VLAN as a case study
• Issues: inefficiencies, sub-optimal router placement
• First study of VLAN usage in a real network (INM’07)

Going Forward…

• Formulate VLAN abstractions and demonstrate their applications
• Generalizing – other campus/enterprise networks

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Thank you

• We are looking for data!
• Please let me know if you have router/switch configurations of an entire enterprise/campus. We will provide useful tools in return. ☺
• Email: sungy@purdue.edu
• Visit http://www.ece.purdue.edu/~isl for more info about our research

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• Questions?

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