Cs540 te630 computer network architecture spring 2009
Download
1 / 16

CS540/TE630 Computer Network Architecture Spring 2009 - PowerPoint PPT Presentation


  • 82 Views
  • Uploaded on

CS540/TE630 Computer Network Architecture Spring 2009. Tu / Th 10:30am-Noon Sue Moon. Routing. What do you remember from undergrad networking courses?. Questions. BGP. De-facto standard inter-domain routing protocol Became popular only in 1995 significant increase in # of ISPs

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' CS540/TE630 Computer Network Architecture Spring 2009' - cian


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Cs540 te630 computer network architecture spring 2009

CS540/TE630Computer Network ArchitectureSpring 2009

Tu/Th 10:30am-Noon

Sue Moon


Routing
Routing

  • What do you remember from undergrad networking courses?



BGP

  • De-facto standard inter-domain routing protocol

  • Became popular only in 1995

    • significant increase in # of ISPs

    • CIDR introduced in 1995

  • Path vector algorithm


Configuration and policy
Configuration and Policy

  • A BGP node decides which routes to share with its neighbor

  • A BGP node can selectively accept and reject messages

  • What to share and what to accept

    • determined by routing policy


Four basic bgp messages
Four Basic BGP Messages

  • Open

    • Establishes BGP session (TCP port #179)

    • Sets the hold timer

  • Notification

    • Report unusual conditions

    • Terminates the TCP session and gives an indication (holder timer expiry, bad peer AS, malformed attribute list, etc.)

  • Update

    • Inform neighbor of new/old routes that become active/inactive

  • Keepalive

    • Inform neighbor that connection is still alive



Attributes
Attributes

  • ORIGIN

    • Who originated the announcement?

    • IGP, EGP or Incomplete (often for static routes)

  • AS-PATH

    • list of AS's

    • useful to detect and prevent loops

  • NEXT HOP

    • For EBGP, IP addr of neighbor that announced

    • For IBGP, if route originated inside, IP addr of neighbor

    • For IBGP, if route originated outside, EBGP node that learned of route, is carried unaltered into IBGP

  • Multi-Exit Discriminator (MED)

  • Local Preference


Attribute multi exit discriminator med
Attribute: Multi-Exit Discriminator (MED)

  • When ASes have multiple interconnecting links

  • Lower, more preferred

  • Non-transitive

AS1

R1

R2

143.248.0.0/16

MED=2

143.248.0.0/16

MED=10

AS2

R3

R4


Attribute local pref
Attribute: Local Pref

143.248.0.0/16

  • Indicates preference among multiples paths for the same prefix

    • higher, more preferred

  • Exchanged between IBGP peers only

  • Often used to select a specific egress point for a particular destination

AS1

AS3

AS2

AS4


Bgp decision process
BGP Decision Process

  • Highest LOCAL-PREF

  • Shortest AS-PATH

  • Lowest ORIGIN (IGP < EGP < Incomplete)

  • Lowest MED

  • Min cost path to NEXT HOP using IGP metrics

  • BGP Router ID to break tie


Input policy engine
Input Policy Engine

  • Inbound filtering

    • filter based on IP prefixes, AS_PATH, community

    • deny = BGP won't reach that prefix via the peer

    • accept = traffic to that prefix via the peer

  • Attribute manipulation

    • Sets attributes on accepted routes

      • E.g.: Specify LOCAL-PREF to set priorities among multiple peers


Output policy engine
Output Policy Engine

  • Outbound filtering

    • forward = peers may route traffic via you

  • Attribute manipulation

    • Sets attributes such as AS-PATH and MEDs


Transit vs nontransit
Transit vs. Nontransit

Transit

AS3

AS1

C3

AS2

C1

C2


Routing engine
Routing Engine

BGP

Input Policy

BGP

Output Policy

BGP Table

IP Routing

Table

Forwarding

Table

OSPF Topology

Shortest Path


References acknowledgements
References & Acknowledgements

  • Some use of Nina Taft's tutorial slides on BGP

  • BGP4 Inter-Domain Routing in the Internet, John W. Stewart, Addison-Wesley, 1998


ad