Agenda Week 1: Internet History and Basic Concepts

Week 2: Routing vs. SwitchingWeek 3: Architecture and Topology TrendsWeek 4: Multimedia (QoS, CoS, multicast)Week 5: ATM vs. IPWeek 6: Routing part 1 (Intro, RIP, OSPF)Week 7: Routing part 2 (BGP, state of the Internet)Week 8: TBD --Guest lecture(s) Week 9: Failure Modes and Fault DiagnosisWeek 10: Product evaluation criteria

Week 2: Switching vs. Routing

• Network Ingredients

• What’s Really on the Wire?

• Inside the Boxes

• Switching & Routing Tradeoffs

• Services, Addresses, & Layers

• Those New-Fangled Hybrids

Network Ingredientsbits, boxes, wires and waves…

• Switching Techniques

• Protocol Families

• The Network Core: Layers 1-3

• Data Link Elements

• Data Link Families

• Mapping Layers to Boxes

• VLANs

Switching Techniques

• Circuit (SDM or TDM or FDM)– Establish fixed end-to-end connection

• Message (Store-and-forward)– No longer used at layers 2-3

• Packet (Frame, FPS, Cell)– Datagram: connectionless, StatMuxed channel– Virtual Circuit: connection-oriented, PVC/SVC

• (Virtual) Circuits over Packets? • Packets over (Virtual) Circuits?• Multicast vs. (Virtual) Circuits?

Packet Protocol Families

• ATM

• IP

• IPX

• Appletalk

• DECNET

• XNS

• PUP

• BNA

• SNA

• OSI

The Network Core: Layers 1-3

3 Network– Key element: global addresses

2 Data Link– Logical Link Control (LLC)– Media Access Control (MAC)

1 Physical/Media (PHY)– e.g. UTP, Coax, Fiber, Wireless

• Do core elements care about layers >3 ?

Data Link Elementsala IEEE 802 and ISO 8802

• Topology – Bus, Ring, Star/Tree… Mesh, Point-to-Point

• Logical Link Control (LLC)– Connection, Connectionless, Connectionless w/ACKs

• Media Access Control (MAC)– Contention, Reservation, Round robin

• Addressing Scheme

Data Link Choices • 802.3 Ethernet• 802.4 Token Bus• 802.5 Token Ring• 802.6 DQDB• 802.7 Broadband• 802.11 Wireless• 802.12 DPAM (100VG)• 802.14 CATV • FDDI• HIPPI• Fibre Channel• SONET• ARCnet, Starlan, Lattisnet

Choosing Ethernet? Welcome to the World of 802.3

• 10Base5, 10Base2, 10Broad36, 10Base-T, 10Base-F… (802.3-1996)

• 100BaseTX, 100BaseT4, 100BaseT2, 100BaseFX… (802.3u, y, aa)

• 1000BaseCX, LX, SX, T (802.3z, ab)

• Full Duplex, Flow Control (802.3x)

But wait! There’s more…Ethernet Frame Formats

• Ethernet II

• IEEE 802.3

• IEEE 802.2 (802.3 + LLC)

• Ethernet SNAP

Mapping Layers to Boxes

• Layer 1 > Repeaters

• Layer 2 > Smart Hubs, Bridges/Switches

• Layer 3 > Routers

• So what’s a “Layer 3 Switch” ??

VLANs • Provide logical grouping of ports/hosts

– Independent of physical topology

• Goals:– Avoid re-addressing when hosts move– Avoid traversing routers unnecessarily– Can provide foundation for multicast

• VLAN Identifiers in 802.1Q– 4096 values– New field in frame header– Based on port, MAC address, or ??– What about adding VID to max size frames?

What’s Really on the Wire?

• MAC, LSAP, & Network Addresses

• Ethernet framing

• Layering and encapsulation example

Network Addresses/Identifiers

• MAC

• LSAP

• Network

• Port

Address Properties

• Global or context sensitive?

• Identifier or Locator?

• Locators: topological or geographic?

• Hierarchical or flat?

• Unicast or multicast or broadcast?

• How assigned?

Two Ethernet Frame Layouts

• Ethernet II– 8 Preamble/SFD

– 6 Destination Address

– 6 Source Address

– 2 Type

– 46-1500 Data

– 4 FCS

• 802.3– 8 Preamble/SFD

– 6 Destination Address

– 6 Source Address

– 2 Length (max 5DC)

– 46-1500 Data

– 4 FCS

Ethernet/IP/TCP Example8 Preamble/SFD6 Destination Address6 Source Address2 Type

1 Version & Header Length 1 Type of Service 2 Total Datagram Length 2 Identification 2 Flags & Fragment Offset 1 Time to Live 1 Protocol 2 Header Checksum 4 Source Address 4 Destination Address ? Options/Padding

2 Source Port2 Destination Port4 Sequence Number4 ACK Number2 Offset, Reserved bits, Flags2 Receive Window Size2 Checksum2 Urgent Pointer? Options/Padding

<<< DATA >>>4 FCS

TCP Header

IP Header

Inside the Boxes

• Connecting Different Kinds of Links

• What goes on Inside the Box

• Routing Approaches

• Packet Classifying/Labeling

• The Key Debate

Connecting Different Kinds of LinksCan we handle differences in...

• Media Type ?

• Data Link Type ?

• Frame Format ?

• Max Frame Size ?

• Speed ?

What goes on Inside the Box?

• Given: Incoming Packet + Internal State

• Result: Forwarding Decision + New State

• State: configuration, routing/forwarding database, buffers, buffer allocations, etc

What goes on Inside the Box -2

• Forwarding

• Routing

• Labeling?

• Error Handling

• Congestion control

• Management

Routing Approaches

• Layer 2– Source routing– Address learning – Protocol (Spanning Tree, 802.1p, Q)

• Layer 3– Source routing– Learning + Sniffing– Protocol (RIP, OSPF, IS-IS, P-NNI)

Packet Classifying/Labeling

• Dynamic, based on examining each packet

• Dynamic, based on real-time flow analysis

• Topological, based on routing info

• Static, based on manual configuration

The Key Debate

“Switch when you can, route when you must”

vs.

“Routers are your friend”

Switching & Routing Tradeoffs

SWITCHES ROUTERSTraffic isolation + +Broadcast isolation - +Address conflict isolation - +Multicast support ? +COS/QOS support ? +Loadsharing uplinks - +Configuration complexity + -Internal complexity + -Protocol independence + -Cost + -

Services, Addresses, & Layers

• Layering Questions

• Services by Address

• Layer 3 Switching

• Fast IP (Cut Thru) Switching

Layering Questions

• Do core devices care about layers >3 ? – Generally no, but...– What about performance?– Impact of speed mismatches on tcp vs. udp

• Do Layer 2 devices care about layers >2 ?– By definition , no, but...– Consider multi-protocol QOS– Multiple Layer 3 protocols force more complexity

into Layer 2

Services based on Layer 2 addresses

• Frame forwarding

• Learning and Spanning tree routing

Services based on Layer 3 addresses/ports

• IP packet forwarding• IP policy or destination-based routing• Constraining IP address conflicts• Multicast• COS/QOS • Loadsharing• Broadcast isolation• Accounting

Layer 3 services that are showing up in switches:

• Multicast support (IGMP vs. 802.1Q)

• COS/QOS? (RSVP vs. 802.1p)

• Fast IP (IPX) forwarding

Layer 3 “Switching”

• Goal: IP packet forwarding with price/performance of Layer 2 switches

• Limited flexibility– IP (and maybe IPX) only– No policy routing, accounting

IP Switching

• Minimum use of Routers

• Most packets “cut thru” to L2 path

• Packet classification strategies vary

• Not just for ATM L2

Where do VLANs fit?

• Enable strange/wonderful topologies

• Gave us cute terms like “One Arm Router”

• Introducing Semi-permeable L2 links:– Use VLANs to limit broadcasts– Normally VLANs connected by routers– Can permit L2 cut-thru between VLANs

just for unicast packets.

Those New-Fangled Boxes

• Ipsilon’s IP Switching

• 3Com’s Fast IP Architecture

• IBM’s ARIS

• Bay’s Layer 3 switch

• Cisco’s Tag Switching

• Rapid City, et al

More Gray’s Networking Nuggets

• Zero and Two are my favorite numbers

• Managing many of the same thing is easier than managing many different things

• One man’s floor is another man’s ceilingProtocol encapsulation is a Good Thing

• Self-describing data is the key to an orderly universe