The document provides an overview of Border Gateway Protocol (BGP) routing concepts. It discusses how BGP allows organizations to exchange routing information with neighbors and control traffic flow. BGP uses autonomous system numbers to identify networks and interior BGP (iBGP) to distribute routes within an organization, while exterior BGP (eBGP) communicates with neighboring networks. The document also notes that most internet service providers peer with each other via BGP at internet exchange points around the world.

1. InteropNet LV 2013
Intro to Wide Area Routing
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2. Agenda
• Introduction
• Review concepts
• Goals of BGP
• BGP in Practice
• Conclusion
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3. Introduction
• The Internet is made up of a bunch of different
organizations
– Big ISPs
– Little ISPs
– Enterprises
• Everyone needs to exchange traffic with everyone
else…mostly
• Need to be able to create policy for how traffic is
sent and received, over what paths and deal with
redundancy
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4. Concept Review
• What is routing?
– Forwarding
• Every packet has a destination IP address
• Address is looked up in the local router’s routing table (FIB –
Forwarding Information Base)
• Packet is routed (forwarded) out the proper interface
– Routing Protocol
• Proscribes a method for how routes get into the FIB
• Many are available that fulfill different needs and situations
– Static
– IGP
» RIP
» EIGRP
» OSPF & ISIS
– EGP
» BGP
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5. Goals of BGP
• Tell your organization’s neighbors about the
destinations you are able to reach
• Provide controls to influence the path traffic
takes to get to you as well as how it leaves
your network
• Distribute global routing information
throughout your network
• Easily filter what you send and what you
receive
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6. BGP Concepts
• AS
– An autonomous system is a network typically
controlled by a single entity, usually one per
company
– Assigned a 4 byte (was 2 byte) number to identify
it, an ASN
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7. BGP Concepts
• iBGP (internal BGP)
– Distributes information throughout your AS
– All iBGP routers must talk directly to all other
routers or use scalability features such as route
reflectors or confederations
– iBGP is NOT an IGP, it is not intended to tell every
router about the paths in your AS, instead it tells
routers about global connectivity
– You must still run an IGP such as OSPF, as BGP
depends on it for local connectivity
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8. BGP Concepts
• eBGP (external BGP)
– eBGP is used to speak to your network neighbors,
usually your upstream transit provider
– Your network neighbors use eBGP to send you
routing information about reachability in the rest
of the world
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9. BGP in practice
• Globally all ISPs “peer” with each other
• An entire ecosystem has developed around
BGP peering, mostly based on the amount of
traffic exchanged
• Exchanges where multiple service providers
come together are located in many major
cities across the world, known as IX (Internet
eXchange)
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10. Routing Table Growth
• Size of the global routing table is currently
around 455,000 routes for v4 and 12,600 v6
routes
• Depletion of IPv4 address space may cause
“deaggregation” of the IPv6 global routing
table, which could result in explosive growth
• Growth of IPv6 also could result in rapid
growth of the global routing table
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Brandon Ross – Chief Network Architect – Network Utility Force – bross@netuf.net