ip atm 0203 - university of...
TRANSCRIPT
© Dr. Z. Sun
1
IP and ATM Internetworking (CIPA, LANE & MPLS)
Dr. Zhili SUNUniversity of Surrey
GuildfordSurrey
GU2 5XHTel: 01483 68 9493Fax: 01483 68 6011
Email: [email protected]
Components of DATA and INTERNET NETWORKING MSc MODULE
(EEM.din, Linked UG EE4.din)
IP and ATM Internetworking(CIPA, LANE & MPLS)
© Dr. Z. Sun
2
IP and ATM Internetworking (CIPA, LANE & MPLS)
Table of Contents
1. Classical IP over ATM (CIPA)2. LAN Emulation (LANE)3. Multi-Protocol Label Switch (MPLS)4. Summary
© Dr. Z. Sun
4
IP and ATM Internetworking (CIPA, LANE & MPLS)
Why IP over ATM?
■ The motivation of “IP over ATM” is to support TCP/IP and applications based on TCP/IP which are widely used long before ATM is developed and to allow interoperability between ATM networks and existing networks
© Dr. Z. Sun
5
IP and ATM Internetworking (CIPA, LANE & MPLS)
IP Over ATM – Protocol Stack
Application
TCP/UDP Layer
IP Layer
AAL 5
ATM Layer
Physical Layer
© Dr. Z. Sun
6
IP and ATM Internetworking (CIPA, LANE & MPLS)
Classical IP Over ATM
■ The “Classical IP Over ATM” provides mechanisms for encapsulation and transmission of IP network layer packets across an ATM Adaptive Layer (AAL) 5 connection
■ It provides a mechanism for the resolution of IP addresses to their corresponding ATM addresses (this is part of the "classical IP over ATM" protocol)
■ It includes the emerging “Next Hop Resolution Protocol (NHRP)“, and
■ IP multicast over ATM via a combination of multicast servers and overlaid point to multi-point connections
© Dr. Z. Sun
7
IP and ATM Internetworking (CIPA, LANE & MPLS)
IP over ATM Encapsulation
■ Encapsulation allows for the multiplexing of multiple packet types (at the network layer) on the same connection:• Conserves connection resources• Saves on connection setup time
■ Multiplex only with UBR, ABR - VBR may require distinct flows
■ Packet must be prefixed with multiplexing field to allow node that receives a network layer packet across an ATM connection:• To know what type of packet has been received• To know what application to pass the packet to
© Dr. Z. Sun
8
IP and ATM Internetworking (CIPA, LANE & MPLS)
IP over ATM Encapsulation (cont.) - RFC 1483
■ Methods for identifying this type of information are:• Subnet Access Protocol / Logical Link Control
(LLC/SNAP) Encapsulation - type of packet identified by header (default encapsulation for IP over ATM)
• VC multiplexing - only single protocol carried across ATM connection with type of protocol identified at connectionsetup (used by LANE); used for direct connectivity between ATM connections
■ Default MTU size is 9180 bytes (+ 8 byte LLC/SNAP header = 9188 bytes) - MTU size can be negotiated up to maximum for AAL 5 (64 Kbytes)
© Dr. Z. Sun
9
IP and ATM Internetworking (CIPA, LANE & MPLS)
IP over ATM Address Resolution - RFC 1577
■ The "classical" view of IP is one in which clusters of IP nodes (hosts and routers) with similar subnet addresses are connected to nodes outside their cluster by IP routers
■ The IETF adhered to this "classical" view by grouping IP nodes into logical IP subnets (LIS) - nodes share the same IP subnet, communicate with the outside through an IP router
■ When node first "comes up" in LIS it establishes a connection with ATMARP server - the node is configured to know the ATM address of the server for address resolution
© Dr. Z. Sun
10
IP and ATM Internetworking (CIPA, LANE & MPLS)
IP over ATM Address Resolution (cont.)
■ ATMARP server (can be part of router - but 1577 recommends that it be another IP station) detects a new LIS client:• Sends Inverse ARP (have ATM address, want IP
address) request to the attaching client• Requests node’s IP and ATM addresses - stores them
in its ATMARP table• Server learn this information by observing client
messages
© Dr. Z. Sun
11
IP and ATM Internetworking (CIPA, LANE & MPLS)
IP over ATM Address Resolution (cont.)
■ To resolve destination IP address:• client sends ATMARP (have IP address, want ATM address)
request to server• server responds with ATMARP reply if address mapping is found• if not returns ATM_NAK
■ ATMARP server sends out periodic Inverse ARP requests to update its addresses - if no response - address eliminated
■ Once client obtains ATM address corresponding to an IP destination - set up connection to that address (ATMARP servers also keeps track of VC’s)
© Dr. Z. Sun
12
IP and ATM Internetworking (CIPA, LANE & MPLS)
Routing across ATM with the Classical mode
■ 1. Routing table maps final destination to next hop■ 2. address resolution table or server maps the next hop IP address to ATM address■ 3. Signalling creates ATM virtual connection between routers■ 4. forward packet over ATM virtual connection
131.227.10.X -> direct 131.227.23.X -> via 131.227.10.2 131.227.45.X -> via 131.227.10.3 131.227.67.X -> via 131.227.10.3
Routing 1
ATM Network
3
131.227.10.1ATM
Switch
131.227.10.2ATM
Switch
131.227.45.94
131.227.23.X
ARP Server
131.227.10.2 -> B 131.227.10.3 -> C
Address Resolution 2
A
B
131.227.10.3ATM
Switch131.227.45.X
C
131.227.67.X
© Dr. Z. Sun
13
IP and ATM Internetworking (CIPA, LANE & MPLS)
IP over ATM Address Resolution (cont.)
■ Disadvantages:• Communicate to host outside of LIS - go through
router even though might be able to connect directly to destination
• Routers become bottlenecks• Can’t establish connection with QoS between the
two nodes
© Dr. Z. Sun
14
IP and ATM Internetworking (CIPA, LANE & MPLS)
Next Hop Resolution Protocol (NHRP)
■ Used instead of a LIS - Non-broadcast Multi-access (NBMA) network
■ Network technology permitting multiple devices to be attached to the same network, but does not easily permit the use of broadcast mechanisms (ATM, X.25, Frame Relay, etc)
■ Could be divided into administrative domains■ NHRP applies only within domain■ Allows access to ingress points of other domains
© Dr. Z. Sun
15
IP and ATM Internetworking (CIPA, LANE & MPLS)
NHRP server (NHS)
■ NHRP server (NHS) instead of ATMARP server■ IP to ATM mapping of nodes associated with an NHS■ IP address prefixes available through routers served
by the NHS Nodes.■ Nodes are configured with ATM address of their NHS■ Then register their ATM and IP address with NHS
using registration packets
© Dr. Z. Sun
16
IP and ATM Internetworking (CIPA, LANE & MPLS)
NHS Configurations
■ “Server" mode• each server has list of destinations served by other
NHS’s• static configuration• good for only small networks
■ “Fabric" mode• servers acquire knowledge of destinations served
by other NHS’s through intra and inter domain routing protocols
© Dr. Z. Sun
17
IP and ATM Internetworking (CIPA, LANE & MPLS)
NHRP Operations
■ Routing - client sends request (in IP packet - all NMBA messages in IP packets) to its NHS asking to resolve an ATM address• if destination served by NHS - returns mapping• if not served - forwards to another NHS - same
algorithm used there• reply sent along reverse route - all NHS’s can learn of
mapping -
© Dr. Z. Sun
18
IP and ATM Internetworking (CIPA, LANE & MPLS)
NHRP Operations (cont.)
■ Future requests - respond without forwarding request■ Direct connection established after address resolution■ Optional capabilities:
• route recording • detect loops• fallback• address aggregation - return subnet mask associated
with an address (i.e. address of firewall associated with ingress NHS of an administrative domain)
© Dr. Z. Sun
19
IP and ATM Internetworking (CIPA, LANE & MPLS)
NHRP issues
■ NHRP likely used on routers for frame relay, X.25■ Enhancements needed for widespread ATM use:
• autoconfiguration (?)• multi-casting• NHRP mechanism very IP specific - everything sent
within IP packets■ RFC1577 compliant system and NHRP may not be
interoperable• have to be connected by a router• connection of either to LANE system also requires a
router
© Dr. Z. Sun
20
IP and ATM Internetworking (CIPA, LANE & MPLS)
IP over ATM Multicasting (IPMC)
■ Multicasting is a process whereby a source host or protocol entity sends a packet to multiple destinations simultaneously using a single local transmit operation
■ The more familiar cases of Unicasting and Broadcasting may be considered as special cases of Multicasting (with the packet delivered to "one" destination or "all" destinations respectively)
■ Most network layer models assume their sources may send their packets to abstract "multicast group addresses"
■ Link layer support is assumed to exist and is provided by such technologies as Ethernet
■ ATM is being utilized as a new link layer technology to support a variety of protocols including IP
© Dr. Z. Sun
21
IP and ATM Internetworking (CIPA, LANE & MPLS)
IP over ATM Multicasting (IPMC)(cont.)
■ With RFC 1483 (2), the IETF defined a multiprotocolmechanism for encapsulating and transporting packets using AAL5 over ATM Virtual Channels (VC’s)
■ Unicast connections are supported by point to point bi-directional VC’s. Multicasting is supported by point to multipoint unidirectional VC’s
■ The key limitation is that the sender must have prior knowledge of each intended recipient and explicitly establish a VC with itself as a root node and the recipients as leaf nodes
■ The Internet Draft IPMC contains more information about IP over ATM Multicasting
© Dr. Z. Sun
22
IP and ATM Internetworking (CIPA, LANE & MPLS)
The future direction of IP over ATM
■ IPng (IPv6) over ATM (internet draft)■ Support for Multicast of IP Packets over ATM
(internet draft)■ Multiprotocol Encapsulation over AAL5 (internet draft)
© Dr. Z. Sun
23
IP and ATM Internetworking (CIPA, LANE & MPLS)
Recommended Texts
■ RFC 1483, Multiprotocol Encapsulation over ATM adaptation layer 5
■ RFC 1577, Classical IP and ARP over ATM■ RFC 1755, ATM signalling Support for IP over ATM■ RFC 2022, Multicast Address Resolution (MARS)
protocols
© Dr. Z. Sun
25
IP and ATM Internetworking (CIPA, LANE & MPLS)
Characteristics of LANs
■ Connectionless traffic■ Delivery of traffic via a shared medium
• Unicast• Broadcast• Multicast
■ MAC address independent of network topology
© Dr. Z. Sun
26
IP and ATM Internetworking (CIPA, LANE & MPLS)
OSI Reference Model
■ LAN Emulation is a Data Link Function
Presentation
Session
Transport
Network
Data Link
Physical
Application
Routing: protocol dependent
Bridging: protocol independent
Repeaters
LLC
MACLAN Emulation
© Dr. Z. Sun
27
IP and ATM Internetworking (CIPA, LANE & MPLS)
Features of LAN Emulation
■ There are currently no ATM specific protocols■ Make an ATM networks looks like a LAN■ LANE is protocol independent■ Integration of ATM and non-ATM devices without
changes to application software■ Traditional LAN services are supported■ Compliance and interoperability with others■ Support multiple emulated LANs on a single ATM
network
© Dr. Z. Sun
28
IP and ATM Internetworking (CIPA, LANE & MPLS)
ATM Forum LANE
■ Separate servers for configuration, address resolution and broadcasts/multicasts
■ ATM “cloud” treated as multiple broadcast domains Emulated LAN (ELAN)
■ Emulated Ethernet (802.3) , Token ring (802.5)
© Dr. Z. Sun
29
IP and ATM Internetworking (CIPA, LANE & MPLS)
LANE Components
■ LE Client (LEC)■ LANE Configuration Server (LECS)■ LANE Server (LES) - MAC to ATM address resolution
for unicast traffic■ Broadcast/Unknown Server (BUS) - forward
multicast, broadcast and unknown unicast packets■ LECS, LES and BUS are known as LAN Emulation
Service which may be implemented in a router, switch, or other ATM attached devices
© Dr. Z. Sun
30
IP and ATM Internetworking (CIPA, LANE & MPLS)
Communication between LECs
■ Each LEC registers MAC address with LES■ When MAC-to-ATM address resolution is required
due to a outgoing data frame:• LE_ARP request sent to LES• DATA frame sent to BUS
■ The ATM address received from the LES is used to send up ATM connection and further data exchanges
■ All broadcasts, multicasts and unknown unicastshandled by BUS
© Dr. Z. Sun
31
IP and ATM Internetworking (CIPA, LANE & MPLS)
LANE Client/Server Architecture
ATM Switch
ATM Switch
ATM Switch
ATM Switch
ATM Backbone
LECS
LES
BUS
LECATM-Attached
Servers
LEC
Edge Device
ATM-Attached Client
ATM-Attached Clients
LEC
LEC
© Dr. Z. Sun
32
IP and ATM Internetworking (CIPA, LANE & MPLS)
LANE Address resolution
ATM Switch
ATM Switch
ATM Switch
ATM Switch
ATM Backbone
LECS
LES
BUS
LEC
Bridge
Edge Device
ATM-Attached Client
ATM-Attached Clients
LEC
1. MAC frame
2. A
PR re
ques
t: M
AC ta
rget
3. A
PR re
ply:
ATM
VCI
4. set-up ATM SVC
5. MAC frame
© Dr. Z. Sun
34
IP and ATM Internetworking (CIPA, LANE & MPLS)
What is MPLS ?
�A connection-orientated forwarding mechanism
�Hop-by-hop or source routing to establish label path
�Uses labels native to the media
�Multi-level label substitution transport
�Simple core - complexity at the edge of a domain
Multi-Protocol Label Switching developed within IETF
© Dr. Z. Sun
35
IP and ATM Internetworking (CIPA, LANE & MPLS)
MPLS Terminology
MPLS: Multi-Protocol Label SwitchingLDP: Label Distribution Protocol LSP: Label Switched PathFEC: Forwarding Equivalence ClassLSR: Label Switching RouterLER: Label Edge RouterER: Explicit RouteCR: Constraint-based RouteTE: Traffic EngineeringQoS: Quality of ServiceCoS: Class of ServiceSLA: Service Level Agreement
© Dr. Z. Sun
36
IP and ATM Internetworking (CIPA, LANE & MPLS)
123
1
2
1
23
3
Dest Out
47.1 247.2 147.3 3
Dest Out
47.1 147.2 147.3 3
IP 47.1.1.1 2
3
1
Dest Out
47.1 147.2 147.3 3
Dest Out
47.1 247.2 147.3 1
Subnet 47.2
Subnet 47.1Subnet 47.3
IP Routing
IP 47.1.1.1 IP 47.1.1.1
IP 47.1.1.1
IP 47.1.1.1
© Dr. Z. Sun
37
IP and ATM Internetworking (CIPA, LANE & MPLS)
PHY
DLink
NET
T/Port
App
Router LSR
PHY
DLink
NET
T/Port
App
IP Routing vs Fast Forwarding
PHY
DLink
PHY
DLink
NET
PHY
DLink
PHY
End System End System
RoutingTable
Longest Prefix Match
FwdingTable
Complex routing decision Simple label swapping
© Dr. Z. Sun
38
IP and ATM Internetworking (CIPA, LANE & MPLS)
Forwarding Equivalence Classes
Packets are destined for different address prefixes, but can be mapped to a common pathPackets are destined for different address prefixes, but can be mapped to a common path
LSPLSR LER
FEC = “A subset of packets that are all treated the same way by a router”
The concept of FECs provides for a great deal of flexibility and scalability
In conventional routing, a packet is assigned to a FEC at each hop(i.e. L3 look-up), in MPLS it is only done once at the network ingress
IP1#L2
IP2#L2
IP1#L1
IP2#L1
IP1#L3
IP2#L3
IP1
IP2
IP1
IP2
LSRLER
© Dr. Z. Sun
39
IP and ATM Internetworking (CIPA, LANE & MPLS)
Req 47.1Map 1:12
MPLS Label Distribution
123
1
2
23
3
2
3
1
Subnet 47.2
Subnet 47.1Subnet 47.3
DestI/F In
47.13
LOutI/FOut
3:501
LInI/F In
3:503
LOutI/FOut
1:401
Req 47.1Map 3:50
Req 47.1
Map 1:40
LInI/F In
1:403
LOutI/FOut
1:122
1
LInI/F In
1:123
DestI/FOut
47.12
Push Label
Swap Label
Swap Label
Pop Label
© Dr. Z. Sun
40
IP and ATM Internetworking (CIPA, LANE & MPLS)
1
1
23
IP 47.1.1.1 2
3
1
Subnet 47.2
Subnet 47.1Subnet 47.3
Data goes in at one end and comes out of the other in the same sequence
LSPs are communication “pipes”
DestI/F In
47.13
LOutI/FOut
3:501
LInI/F In
3:503
LOutI/FOut
1:401
LInI/F In
1:403
LOutI/FOut
1:122
LInI/F In
1:123
DestI/FOut
47.12
Label Switched Path (LSP)
IP 47.1.1.1
IP 47.1.1.1#3:50
IP 47.1.1.1#1:40
IP 47.1.1.1#1:12
© Dr. Z. Sun
41
IP and ATM Internetworking (CIPA, LANE & MPLS)
#612
#5
Vanilla LDP builds that tree using existing IP routing tables to route the control messages
A Vanilla LSP is actually part of a tree from every source to that destination (unidirectional)
#963
#14
#99
#311
#311
#311
#311
#14
#99
#963#462
#216
“Vanilla” Label Switched Path
© Dr. Z. Sun
42
IP and ATM Internetworking (CIPA, LANE & MPLS)
Maximize utilization of links and nodes throughout the network
Select links in order to achieve required delay, grade-of-service
Spread the network traffic across network links, minimize impact of single failure
Ensure available spare link capacity for re-routing traffic on failure
Meet policy requirements imposed by the network operator
Traffic Engineering is the process of mapping traffic demand onto network resources
Purpose of traffic engineering:
Traffic Engineering
© Dr. Z. Sun
43
IP and ATM Internetworking (CIPA, LANE & MPLS)
IP routing causes data to over-utilize best paths and under-utilize less good paths
Basic LDP is fast, simple forwarding / switching, BUT data follows same route as normal IP data path causing data to over-utilize best paths and under-utilize less good paths
We need…
Why Constraint-based Routed – LDP (CR-LDP)?
A topology database that knows about link attributes
A label distribution protocol that goes where it’s told
Constraint Based Routing provides a mechanism for selecting paths based on CHOSEN Criteria (not just a one criterion)
© Dr. Z. Sun
44
IP and ATM Internetworking (CIPA, LANE & MPLS)
CR-LDP Provides…
�Simple protocol based on LDP, output of MPLS WG
�basic hop-by-hop LDP is not needed
�Runs on TCP (like LDP) = Reliable
�Hard State (like LDP) = Scalable
�Supports Traffic Engineering with QoS Support
�Both Explicit Routes and Loose routes supported
�Demonstrated Interoperability
© Dr. Z. Sun
45
IP and ATM Internetworking (CIPA, LANE & MPLS)
IP 47.1.1.1
Subnet 47.2
Subnet 47.1Subnet 47.3
Least cost congestion “hot spots” can be avoided
Using Explicit Routing any chosen path can be setup across the MPLS domain
Explicitly Routed LSP using CR-LDP
Operator has routing flexibility(policy-based, QoS-based)
Pre-computed backup paths for resiliency
IP 47.1.1.1
© Dr. Z. Sun
46
IP and ATM Internetworking (CIPA, LANE & MPLS)
Label Stacking
Label stacking – facilitates scaling and inter-operator working
Carrier MPLS Domain
LSP1 LSP1
LSP2
LSP3
LSP2
LSP3
Access ProviderMPLS Domain
Access ProviderMPLS Domain
IP-A LSP1
IP-B
IP-A
IP-BLSP2
LSP1 IP-A
IP-BLSP2
LSP3
LSP3
LSP1 IP-A
IP-BLSP2
IP-A
IP-B
© Dr. Z. Sun
47
IP and ATM Internetworking (CIPA, LANE & MPLS)
Summary (1/2)
Fast forwarding based on label swapping
Decouples routing and forwarding in IP networks and can co-exist with other protocols
Facilitates the integration of ATM and IP
Enables the use of explicit routing for traffic engineering in IP networks
Promotes the partitioning of network functionality (complexity at edge)
© Dr. Z. Sun
48
IP and ATM Internetworking (CIPA, LANE & MPLS)
Summary (2/2)
Improved routing scalability through stacking of labels
MPLS is “multiprotocol” below (link layer) as well as above (network layer), providing for consistent operations, interworking across multiple technologies
MPLS positioned as end-to-end forwarding paradigm
Flexible FEC to Label binding allows for full multi-service support