16-04-2012, 11:10 AM
Multiprotocol Label Switching
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Instructions (Cont)
q Please email your positive and negative
feedback about the quality of the reception
as well as the content with a subject field
of “Feedback” to mbone[at]netlab.ohio-state.edu
q If you are not able to receive the program due to some
technical difficulties, please email “Feedback” to
mbone[at]netlab.ohio-state.edu
q Please email technical questions with the subject field
“Question” to mbone[at]netlab.ohio-state.edu. We will
try to answer selected questions live.
The Ohio State University Raj Jain
6-4
q Review of MPOA and IP Switching
q Tag Switching (CISCO)
q ARIS (IBM)
q Multi-protocol label switching
The Ohio State University Raj Jain
6-5
Disclaimer
q This technology is currently evolving.
Þ All statements are subject to change.
q Features not in a scheme may be implemented later in
that scheme.
q Problems claimed to be in a scheme may later not be a
problem.
The Ohio State University Raj Jain
6-6
L3 Switching
q Layer 3 forwarding at wire speeds
m Switching based on Layer 3 (L3) header
m Switched IP forwarding
m Several million packets per second
(Mpps)
m 8 Mpps announced by ODS
q Layer 2 switching Þ Large flat networks
m Problem: Broadcast, security
m Solution: Virtual LANs (VLANs)
Þ Need routing between VLANs
The Ohio State University Raj Jain
6-7
Technology Evolution
q New technology gets absorbed by the old
q FDDI Þ 100 Mbps Ethernet
q Fiber Channel Þ Gigabit Ethernet
q ATM Switches Þ LAN switches
q ATM ELANs Þ VLANs
q ATM shortcuts Þ L3 Switching
The Ohio State University Raj Jain
6-8
MPOA
q Multiprotocol over ATM
q Extension of LANE
q Solves the problem of needing routers between
emulated LANs
q Uses NHRP to find the shortcut to the next hop
q NHRP servers communicate with each other to find
the destination
q No routing (reassembly) in the ATM network
NHS R NHS
H ELAN1 ELAN2 H
The Ohio State University Raj Jain
6-9
IP Switching
q Developed by Ipsilon
q Routing software in every ATM
switch in the network
q Initially, packets are reassembled by the routing
software and forwarded to the next hop
q Long term flows are transferred to separate VCs.
Mapping of VCIs in the switch Þ No reassembly
R R
S S
The Ohio State University Raj Jain
6-10
Cell Switched Router (CSR)
q Proposed by Toshiba
q Flow driven (similar to Ipsilon)
q VCID separate from VCI Þ Switches between CSRs
q Upstream assigns a VCID and sends downstream
Cell
Switched
Router
VCID = 4
ATM
Switch
ATM
Switch
Cell
Switched
Router
5 3 6
The Ohio State University Raj Jain
6-11
CSR (Cont)
q VCs are set up in advance
and are bounded as needed
q Classifies flows by IP source/destination address pair
q Soft connections Þ Periodically refreshed
The Ohio State University Raj Jain
6-12
Tag Switching
q Entry router/switch attaches a label (tag) to the packet
based on the route
q Switches switch packets based on labels.
Do not need to look inside Þ Fast.
q Tags have local significance
Þ Different tag at each hop (similar to VC #)
q Exit router/switch strips off the tag
R S R
S
S
Tag Switch/Router Tag Switch
Tagged
UntaggedPacket Untagged Packet
Packet
The Ohio State University Raj Jain
6-13
Tag Switching
q Proposed by CISCO
q Similar to VLAN tags
q Tags can be explicit or implicit L2 header
L2 Header Tag
q Ingress router/host puts a tag
H
R
R
R H
H
Untagged H
Packet Tagged packet
The Ohio State University Raj Jain
6-14
Tag Switching (Cont)
q One VC per routing table entry
q One memory reference compared to 4-16
in router
R
164.107/16
<3>
R
164.107/16
<2>
164.107/16
<64>
164.107/16
<5>
R
164.107/16
<3>
64
3
3
5 3
The Ohio State University Raj Jain
6-15
ARIS
q Aggregate Route-Based IP Switch
q Proposed by IBM
q Topology based. One VC per egress router.
q Egress router initiates the setup of switched path
q Supports LAN media switching
R
R R R
R
R
R
The Ohio State University Raj Jain
6-16
ARIS (Cont)
q mpt-to-pt VC Þ VC merge
q Integrated Switch Routers (ISRs)
q Globally unique labels Þ Each ISR has a VCI block
ATM
Switch
5 5 5
5 5 5
3 3 3
The Ohio State University Raj Jain
6-18
Switched IP Forwarding: Comparison
Issue IP Switch CSR Tag ARIS
Datalink ATM ATM, FR ATM, FR,
Ethernet
ATM, FR
Network
Layer
IP IP IP, XNS,
…
IP
Initiator Downstream Both Both Egress
VC Setup
Protocol
IFMP FANP TDP ARIS
Mapping Traffic Traffic Topology Topology
# of VCs # of L4
flows
# of L3
flows
# of routes # of Egress
routers
The Ohio State University Raj Jain
6-19
MPLS
q Multiprotocol Label Switching
q IETF working group to develop
switched IP forwarding
q Initially focused on IPv4 and IPv6.
Technology extendible to other L3 protocols.
q Not specific to ATM. ATM or LAN.
q Not specific to a routing protocol (OSPF, RIP, ...)
q Optimization only. Labels do not affect the path.
Only speed. Networks continue to work w/o labels
q Complete spec by the end of 1997
The Ohio State University Raj Jain
6-20
Terminology
q Label = Short fixed length,
physically contiguous, locally significant
q Stream = S flows = pt-pt, pt-mpt, mpt-pt, mpt-mpt
q Stream Merge Þ Stream = S streams
q Label information base (LIB) @ Routing info base
q Label distribution protocol (LDP) @ Routing protocols
q MPLS edge node = Egress or ingress node
MPLS Domain
The Ohio State University Raj Jain
6-21
Label Assignment
q Binding between a label and a route
q Traffic, topology, or reservation driven
q Traffic: Initiated by upstream/downstream/both
q Topology: One per route, one per MPLS egress node.
q Labels may be preassigned
Þ first packet can be switched immediately
q Reservations: Labels assigned when RSVP “RESV”
messages sent/received.
q Unused labels are "garbage collected"
q Labels may be shared, e.g., in some multicasts
The Ohio State University Raj Jain
6-22
Label Format
q Labels = Explicit or implicit L2 header
q TTL = Time to live
q CoS = Class of service
q SI = Stack indicator