Network Router Architectures - Ohio Supercomputer Center

flutteringevergreenNetworking and Communications

Oct 29, 2013 (3 years and 9 months ago)

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CSE677: Lecture

“Router Architecture and

Configuration Basics”


Prasad Calyam
,

Senior Systems Developer/Engineer

OARnet, A Division of Ohio Super Computer Center

pcalyam@osc.edu


21
st

May 2007

Topics of Discussion


What kinds of Routers are on the Internet?


Introduction to Router Architecture


Switching Fabrics


Input and Output Port Queuing


Look
-
up Requirements and Techniques


How to access Router’s features?


Introduction to Cisco IOS


Configuring OSPF and BGP on a Cisco router


Conclusion

What kinds of Routers are on the Internet?


Router

is a physical device in a network that
directs packets to their intended destinations


Routers are used at Three levels in the Internet


Access Level


Ex. Cisco 700 to 2500 Series


Enterprise/Distribution Level


Ex. Cisco 2600 to 3600 Series


Core/Backbone Level


Ex. Cisco 12000 GSR Series

Types and Sizes of Routers

Home Networking

or Access Router

10s of $$

Routers for Small/Medium
sized Enterprise Networks

100s
-
1000s of $$

Router for Large
Backbone Networks

> 10,000s of $$

IP Network View: ISPs

(E.g. OARnet
-

Ohio, MERIT
-

Michigan,…)

(E.g. Time Warner, SBC Yahoo, WOW,…)

(E.g. Internet2
-

USA, DANTE
-

Europe, CANARIE
-

Canada,…)

Point of Presence (PoP)


PoP (Point of Presence)

is a
term used to reference a
physical location where network
equipment such as routers,
switches, etc. are deployed.


It is also where
telecommunication lines meet


An ISP hands
-
off traffic to
another ISP

In
-
class Problem


“What is the approximate diameter of the Internet?”


Diameter definition: Maximum number of routers between two
extreme hosts on the Internet.


You can discuss with your neighbors


HINT:

Imagine how IP handles packets that may indefinitely
circulate on the Internet and ultimately cause flooding.


Router Architecture Overiew


Router’s Primary Functions


Orchestrate

routing algorithms/protocol (RIP, OSPF, BGP)


Switching
datagrams from incoming to outgoing link at line
speed



Router Interface

Router Internal Functions

Input and Output Port Queuing


Input Queue


Line speed > switching fabric speed







Output Queue


Line speed < switching fabric speed


Data link processing
involves the Frame Check
Sequence calculation to
confirm whether a frame is
corrupted
-

before passing it
to a switch fabric


Queueing (delay) and loss
occurs due to input or output
port buffer overflow!


Scheduling discipline

performs contention
management by choosing
among queued datagrams for
transmission;
FIFO, QoS

TOS based, …


Switching Fabrics


Switching fabric transfers
datagrams from input port memory
to appropriate output port memory
(avoids contention)


Switching via
Shared memory


Speed is limited by memory access
speed (i.e., Read/Write speed)


Switching via
Shared Bus


Single frame at a time


Serial;
Buffering allows Parallel frame
handling


Speed is limited by bus capacitance


1 Gbps bus, Cisco 1900: sufficient
speed for access and enterprise
routers (not regional or backbone)


Switching via
Space division
(crossbar)


Each input interface has access to
the matrix that directly connects to
the multiple output interfaces


Speed is limited by the scheduler

Look
-
up Requirements


Line speed switching versus forwarding decision making


IP lookup algorithm decides which output interface needs
to be selected for packet forwarding


Requirements


Speed: Number of memory accesses


Storage requirements: Amount of memory


Scalability


With length of prefix


IPv4 unicast (32b), IPv6 unicast (128b)


With size of routing table


Number and Types of QoS options


Flexibility in implementation (allows customization for
different protocols)


In
-
class Problem


“If you are a router architect, how would you design
a router to handle routing decisions?”


Consider the different lookup requirements


You can discuss with your neighbors


HINT:

Recall the data search and retrieval tricks used in your
database course


Look
-
up Techniques

Networking
Protocol

Lookup
Mechanism

Techniques Used

MPLS, Ethernet

Exact match
search


Direct lookup



Not suitable for large tables,
ex.
>

10
12


Hashing using Hash Functions


Binary/Multi
-
way Search Trie/Tree


Associative lookup using
Content
Addressable Memory (CAM)


Compares all entries in parallel
against incoming data

IPv4, IPv6

Longest
-
prefix
match search

-
Radix trie and variants

-
Compressed trie

-
Binary search on prefix intervals

Content Addressable Memory


CAM is a special type of computer memory used in
certain very high speed searching applications


It utilizes a
hardware
-
based

search
-
table concept to
provide a higher performance alternative to software
-
based searching algorithms


CAM can be compared to the inverse of the RAM. When
read, RAM produces the data for a given address.
Conversely, CAM produces an address for a given data
word (if data word is found in memory)


CAM is much faster than RAM


entire memory search in
one clock cycle


CAM is very expensive compared to RAM


because
additional comparison circuitry is required for every bit
to match stored bits with input bits

How to access Router’s features?


Cisco Internetwork Operating System (IOS)


It’s the kernel of all Cisco routers and switches


It controls hardware to allow for configuring, monitoring and
troubleshooting various router functions. Ex.:


Setup of various network protocols


Add security to control access and stop unauthorized network use


Memory in a Cisco Router


Cisco IOS resides in the Flash Memory


Startup configurations reside in NVRAM


All other temporary tables/buffers are created in RAM


Cisco IOS had 3 command modes of operation


Router> “
User Mode” to generally view statistics and
stepping
-
stone to logging into privileged mode


Router# “
Privileged Mode” to view the router’s configuration,
restart system, logon to config mode, …


Router(config)# “
Configuration Mode” to change the
router’s configuration, configure interfaces, …


Router# ?
Gives a list of all features available

Router# ?

Configuring OSPF on a router


OSPF


Link
-
state routing protocol that utilizes Dijkstra’s Shortest
Path First Algorithm which allows for faster network
convergence


Configuration Steps


Configure IP addresses on Router Interfaces


R1 and R2


Create loopback (logical/virtual interface) on R1 and R2


Create OSPF on R1 with Area0


Create OSPF on R2 with Area0


Establish OSPF on R1 and R2


“Ping” both logical interfaces!




#sh ip route ospf

Configuring BGP on a router


BGP


Internet routing protocol that allows
sharing of routing information
between different autonomous
systems


Configuration Steps for eBGP


Configure IP addresses on Router
Interfaces


R1 and R2


Create loopback (logical/virtual
interface) on R1 and R2


Create BGP on R1 by creating AS 100
(Ex. OSU) domain


Create BGP on R2 by creating AS 200
(Ex. UC) domain


Establish BGP between R1 and R2


“Ping” both logical interfaces!

#sh ip route bgp

Questions?