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