1. Chapter 4: Advanced Internetworking
CS 3470, Section 1

2. Intra-AS and Inter-AS Routing
C.b
Gateways:
perform inter-AS routing amongst themselves
perform intra-AS routers with other routers in their AS
B.a
A.a b
A.c c a a C b a B d c A b

3. Intra-AS and Inter-AS Routing
C.b
Gateways:
perform inter-AS routing amongst themselves
perform intra-AS routers with other routers in their AS
B.a
A.a b
A.c c a a C b a B d c A b
network layer
inter-AS, intra-AS routing in
gateway A.c
link layer
physical layer

4. Intra-AS Routing Algorithms
We have already talked about two intra-AS routing algorithms:
Link state routing
Distance vector routing

5. Link State vs Distance Vector
Tells everyone about neighbors
Controlled flooding to exchange link state
Dijkstra’s algorithm
Each router computes its own table
May have oscillations
Tells neighbors about everyone
Exchanges distance vectors with neighbors
Bellman-Ford algorithm
Each router’s table is used by others
May have routing loops
Now lets compare these two routing protocols. Under link state, a router tells everyone about its neighbors using controlled flooding. Distance vector case a router communicates with neighbors only to inform about everyone.
Link state each router gathers global information and computes its own table using Dijkstra’s algorithm. Distance vector performs distributed computation using other routers tables.
We saw that distance vector can cause routing loops. There may be frequent changes in routes in the case of link state. This results in out of order delivery of packets which is undesirable.
Both these approaches have advantages and disadvantages. Both are used in the Internet. OSPF is the most popularly used intra-domain routing protocol that is based on link state. RIP is based on distance vector which is being taken over by OSPF. BGP is an inter-domain protocol that uses path vectors.

6. RIP RIP == Routing Information Protocol
RIP is a distance vector implementation
Instead of advertising costs to the next router, RIP advertises the cost to the next network.
(network_address,
distance)
pairs

7. Large Routing
OSPF
BGP

8. OSPF
One of the most widely-used link-state routing protocols is Open Shortest Path First
Open, nonproprietary standard created by the Internet Engineering Task Force
Shortest Path First is an alternative name for link- state routing
Hierarchical – can divide the system into “areas.”

9. OSPF Roles Internal router :: a level 1 router.
Backbone router :: a level 2 router.
Area border router (ABR) :: a backbone router that attaches to more than one area.
AS border router :: (an interdomain router), namely, a router that attaches to routers from other ASs across AS boundaries.

10. OSPF advertisement
Indicates
LSA type
Indicates
link cost

11. OSPF LSA types Router link advertisement [Hello message]
Network link advertisement
Network summary link advertisement
AS border router’s summary link advertisement
AS external link advertisement

12. Border Gateway Protocol and Autonomous Systems
Border Gateway Protocol (BGP)
Assumes that the Internet is an arbitrarily interconnected set of ASs.
Today’s Internet consists of an interconnection of multiple backbone networks (they are usually called service provider networks, and they are operated by private companies rather than the government)
Sites are connected to each other in arbitrary ways

13. Border Gateway Protocol and Autonomous Systems
Assumes the Internet is an arbitrarily interconnected set of AS's.
Define local traffic as traffic that originates at or terminates on nodes within an AS, and transit traffic as traffic that passes through an AS.

14. Border Gateway Protocol and Autonomous Systems
We can classify AS's into three types:
Stub AS: an AS that has only a single connection to one other AS; such an AS will only carry local traffic

15. Border Gateway Protocol and Autonomous Systems
We can classify AS's into three types:
Multihomed AS: an AS that has connections to more than one other AS, but refuses to carry transit traffic

16. Border Gateway Protocol and Autonomous Systems
We can classify AS's into three types:
Transit AS: an AS that has connections to more than one other AS, and is designed to carry both transit and local traffic (backbone provider)

17. BGP
The goal of Inter-domain routing is to find any path to the intended destination that is loop free
We are concerned with reachability than optimality
Finding path anywhere close to optimal is considered to be a great achievement

18. BGP
Scalability: An Internet backbone router must be able to forward any packet destined anywhere in the Internet
Having a routing table that will provide a match for any valid IP address
Autonomous nature of the domains
It is impossible to calculate meaningful path costs for a path that crosses multiple ASs
A cost of 1000 across one provider might imply a great path but it might mean an unacceptable bad one from another provid
Issues of trust
Provider A might be unwilling to believe certain advertisements from provider B

19. BGP Each AS has: One BGP speaker that advertises:
local networks
other reachable networks (transit AS only)
gives path information
In addition to the BGP speakers, the AS has one or more border “gateways” which need not be the same as the speakers
The border gateways are the routers through which packets enter and leave the AS

20. BGP
BGP does not belong to either of the two main classes of routing protocols (distance vectors and link-state protocols)
BGP advertises complete paths as an enumerated lists of ASs to reach a particular network

21. IPv6
Moving on to IPv6!
For more information, refer to Section in your textbooks

22. Why not IPv4? IPv4 addresses have become relatively scarce
NATs help by promoting reuse of address space, but
They do not support standards-based network layer security or the correct mapping of all higher layer protocols
Can create problems when connecting two organizations that use the private address space.

23. Why not IPv4?
Additionally, the rising prominence of Internet-connected devices and appliances ensures that the public IPv4 address space will eventually be depleted.
It would be nice to not have to rely on protocols like DHCP to configure addresses

24. Why not IPv4?
Private communication over a public medium like the Internet requires encryption services that protect the data being sent from being viewed or modified in transit.

25. Why IPv6? IPv6 is required to include IPsec.
IPsec allows authentication, encryption, and compression of IP traffic.
The benefit of this is that all applications on a machine can benefit from encryption and authentication, and that policies can be set on a per-host (or even per-network) basis, not per application/service.

26. Why IPv6?
IPv6 uses a 128-bit address instead of the 32-bit address of IPv4.
This doesn't give 4 times the addresses of IPv4 but rather the number of IPv4 addresses squared twice.
A couple of articles out there have stated that this works out to billions of billions of addresses for every square meter on the planet.

27. IPv6 Addressing
An IPv6 address is written as hexadecimal values (0-F) in groups of four separated by colons, like: A223:BB34:0000:0000:0000:0099:DA78:5679
Strings of zeros can be dropped and leading zeros in a number group can be dropped, so the example above would shorten to
A223:BB34::99:DA78:5679.

28. IPv6 Addressing IPv4 isn't left out completely
IPv4 addresses can be expressed in IPv6 form as follows: :0000:0000:0000:0000:0000: –which can be shortened to ::
This makes transitioning a bit easier.

29. IPv6 Headers
4-bit version field that defines the protocol in use (default is 6),
8-bit traffic class field to allow for Quality of Service (QOS)-type services
20-bit flow label field that provides path management services

30. IPv6 Headers
8-bit next header field that indicates to routers that there is another header following the main header,
a 16-bit payload length field that gives the length of the payload in octets
hop limit field that indicates the number of hops a packet can take before being discarded

31. IPv6 Headers
The header ends with the 128-bit source and destination fields.
The total length of the header is 40 bytes compared to the 20-byte header in Ipv4.
Use of the next header field allows headers to be chained after the main header. These auxiliary headers can add routing, encryption and authentication features.

32. IPv6
IPv6 adds significant extra features that were not possible with IPv4.
Automatic configuration of hosts (similar and DHCP)
Extensive multicasting capabilities
Built-in security using authentication headers and encryption
Built-in support for QOS and path control

33. IPv4 and IPv6 Headers

34. IPV4 and IPV6 Addressing Ipv4: IPV6 32 bits ~ 4,200,000,000 addresses
340,282,366,920,938,463,463,374,607,431,768,211,456 nodes
Addresses have “scope”
Link Local
Unique Local
Global
Addresses have lifetime
Valid and preferred lifetime facets
Unicast, Multicast, and Anycast...but no broadcast

35. IPv6 Addressing Same “longest-prefix match” routing as IPv4 CIDR
e.g: 2001:db8:12::/40
Two Different Classes
Link-State (i.e., OSPF, ISIS, etc.)
Distance-Vector (i.e., RIP, IGRP, etc.)
Autonomous System / Routing Domain
Interior Gateway Protocols (IGPs) i.e., OSPFv3, ISIS for IPv6, RIPng, EIGRP for IPv6
Exterior Gateway Protocols (EGPs) Multi-Protocol Extensions for BGP4

36. IPv6 Addressing
The idea behind having fixed-width, 64-bit wide host identifiers is that they aren't assigned manually as in IPv4.
Instead, v6 host addresses are recommended to be built from so-called EUI64 addresses.
EUI64 addresses are 64-bits wide, and derived from MAC addresses of the underlying network interface.
For example, with Ethernet, the 6-byte (48-bit) MAC address is usually filled with the hex bits "fffe" in the middle

37. What's your address, MAC?
For example, with Ethernet, the 6-byte (48-bit) MAC address is usually filled with the hex bits "fffe" in the middle -- the MAC address :23:45:67:89:ab results in the EUI64 address :23:45:ff:fe:67:89:ab which again gives the host bits for the IPv6 address. ::0123:45ff:fe67:89ab

38. End of Chapters 3-4