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© 1999, Cisco Systems, Inc.
Deploying IP Switching Solutions Session 312
312 0986_05F9_c2
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312 0986_05F9_c2
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© 1999, Cisco Systems, Inc.
Deploying IP Switching Solutions Session 312
312 0986_05F9_c2
© 1999, Cisco Systems, Inc.
Copyright © 1998, Cisco Systems, Inc. All rights reserved. Printed in USA. 0986_05F9_c2.scr
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Introduction/Agenda
• Many Switching Paths • Evolution • Benefits/Trade Offs • Some Switching Paths Deprecated
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Switching Evolution
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Process Switching
• Process context • Earliest Cisco IOS ™ switching mode • Least performance • Uses IP routing table
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Deployment Information
• Available in all platforms • Available by default
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Fast Switching
Frame Packet
Packet
IP Cache
Packet
Frame Packet
Layer 3 Switching Layer 2 Rewrite
• Interrupt level • IP cache lookup 312 0986_05F9_c2
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Fast Switching Process Switching
Frame Packet
No IP Cache
Yes Frame Packet
• Cache on demand • Require process switching • Traffic driven 312 0986_05F9_c2
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Fast Switching
• Recursion resolution at process level • Classfull • Per-destination load sharing • Cache entries aged to limit the cache size
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Fast Switching • Overhead inherent to cache maintenance Route change Interface state change Configuration change
• Assumes finite number of active flows 312 0986_05F9_c2
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Deployment Information
• Available in all platforms • Enabled using the ‘ip route-cache’ interface command • Deprecated
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Autonomous/SSE Switching • Hardware/microcode assist • Extension of fast switching cache • Increased performance/reduce functionality • Cache misses bubble up the packet • Same issues as fast switching • Now deprecated 312 0986_05F9_c2
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Optimum Switching
• Extension of fast switching • Optimum cache • Optimized for higher performance • Same issues • Deprecated in Cisco IOS 12.0 312 0986_05F9_c2
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Distributed Fast Switching RSP
• Available with intelligent IPs • Distributed cache
IP VIP First Packet Subsequent Packets
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Deployment Information
• Available in Cisco 7500/7200 • Enabled using the ‘ip route-cache optimum’ interface command • Deprecated
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Evolution: SPD
• Selective Packet Discard • Major route change causes cache churn • Triggers large number of packets to process level • Overwhelms CPU and causes control packet drop • Causes prolonged instability 312 0986_05F9_c2
• SPD to differentiate control traffic • Precedence bit used to mark control packets (e.g. BGP updates) • Avoids dropping control packet • Increased system stability
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Cisco Express Forwarding
• New topology driven architecture • Main components Forwarding Information Base (FIB) Adjacency table
• No process switching of packets 312 0986_05F9_c2
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Cisco Express Forwarding
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Routing Table
ARP/Map Table
FIB Table
Adjacency Table
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Adjacency Table
• Maintains IP address to Mac-rewrite mapping • Populated by ARP table, Frame Relay map table and ATM map table, etc. • Mac-rewrite of the nexthop is all that’s required to switch packet 312 0986_05F9_c2
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FIB Table • • • • • •
Shadow copy of the IP routing table Classless Routing protocol independent One for each route in IP routing table Each entry has one or more path Each path has nexthop IP address and nexthop interface • Each path points to an adjacency 312 0986_05F9_c2
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CEF Operation • FIB entry created when routes are added to IP routing table • If connected, new FIB entry points to the corresponding adjacency • Ready to switch packets • Non-connected prefix requires more work 312 0986_05F9_c2
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CEF Operation
• Recursion resolution • Done in the background • Recursive lookup for non-connected nexthop to find the connected nexthop • Once resolved, ready to switch
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CEF Switching
Frame Packet
FIB
Packet
Packet
Frame Packet
Layer 3 Switching Layer 2 Rewrite
• Interrupt level • FIB entry look up 312 0986_05F9_c2
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CEF Switching Routing Information Base
FIB
Frame Packet In
Adjacency Information
Frame Packet Out
• If FIB lookup fails, packets are dropped • Full knowledge at interrupt level 312 0986_05F9_c2
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Distributed CEF FIB
RIB CEF Process
RP
ADJ
ARP
Inter-Process Communication (IPC)
CEF Process FIB
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ADJ
CEF Process FIB
ADJ
CEF Process FIB
ADJ
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CEF Load-Sharing Destination
Sources
• Per packet and enhanced per destination • Enhanced per destination is based on source and destination IP addresses • Each destination flow takes a single, separate path • Reduces need for per packet load-sharing 312 0986_05F9_c2
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Deployment Information
• Available in GSR, Cisco 7500, 7200, 4500, 4700, 3600, 2600 and 1600 • Enabled using the ‘ip cef [distributed]’ global command • Recommended method
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NetFlow Switching • Many features require flow identification • NetFlow accelerates such features • Flow identifier includes source IP address, source port, destination IP address and destination port • Doesn’t hold switching decisions 312 0986_05F9_c2
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NetFlow Switching • Relies upon fast cache or CEF to switch packets • Maintains accounting and additional information like source AS, destination AS per flow • Also contains feature specific information per flow 312 0986_05F9_c2
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NetFlow Operation • First packet of a flow triggers flow-state creation • Flow-accelerated features informed about the new flow • Interested features register with the flow • Interested features act on subsequent packets of the flow 312 0986_05F9_c2
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NetFlow Operation
Header • Sequence number • Record count • Version number
Flow Record
…
Flow Record
NetFlow Cache
• Flow cache manager expires flows No traffic/long life/TCP flags/cache full/etc.
• Intelligent cache aging ensures that cache entries are always available • Router exports groups of expired flows every second • Export uses UDP datagrams with sequence numbers 312 0986_05F9_c2
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NetFlow—Onboard Aggregation
• Per flow data not always needed • Often only subset of the exported information is needed • Onboard aggregation before exporting the data • Reduced data to export—scalable 312 0986_05F9_c2
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NetFlow Switching • Distributed NetFlow switching in intelligent linecards • Fast-cache based NetFlow has same problems as fast switching • CEF-based NetFlow leverages the benefits of CEF • CEF based NetFlow is scalable and stable 312 0986_05F9_c2
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Deployment Information
• Available in GSR, Cisco 7500, 7200, 4500, 4700, 3600, 2600 and 1600 • Enabled using ‘ip route-cache netflow’ interface command
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Multiple Switching Paths
• Cascading switching paths • Optimum -> fast switching -> process switching • CEF replaces optimum switching • CEF -> fast switching -> process switching 312 0986_05F9_c2
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Multiple Switching Paths
• CEF automatically bubbles packet for unsupported features • In some platforms packets bubbled to generate ICMP messages • DCEF -> CEF -> fast switching -> process switching 312 0986_05F9_c2
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Tag Switching/MPLS • Integrates Layer 3 scalability and flexibility with Layer 2 performance and traffic management • Avoids complex overlay model • Reduces signaling overhead • Media independent • Foundation for many new services 312 0986_05F9_c2
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Tag Switching/MPLS Components of Tag Switching
• TDP • TIB • CEF
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Tag Switching/MPLS—Example Local Local Remote Remote Address Address Interface Interface Tag Tag Prefix Tag Tag Prefix
X X X X
11 22
128.89 128.89 171.69 171.69
... ...
... ...
... ...
11 22
Tag Tag Information Information Base Base
Local Local Remote Remote Address Address Interface Interface Tag Tag Prefix Tag Tag Prefix
11 22
77 55
128.89 128.89 171.69 171.69
00 44
33
... ...
... ...
128.89 0
I/f 1 171.69.12.1 171.69.12.1 Data Data
2 171.69.12.1 171.69.12.1 Data Data Untagged Untagged Data Data
I/f 4
171.69
5 171.69.12.1 171.69.12.1 Data Data 171.69.12.1 171.69.12.1 Data Data
• CEF forwarding table populated with routing topology information
Untagged Untagged Data Data
• Each route/prefix mapped to a tag value • Switching decision then only ‘label-swaps’ via the Tag Information Base (TIB) 312 0986_05F9_c2
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Deployment Information
• Available in GSR, Cisco 7500, 7200, 4500, and 4700
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Features in Different Switching Paths
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Selection Criteria
• Depends on the feature required • Depends on the platform required • Hybrid switching solutions
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CEF Features
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CEF—RPF Check • Source address spoofing denial-of-service attack • Unicast reverse path forwarding check with CEF • Per packet source address check to make sure source is reachable via the received interface • Failed packets counted and discarded 312 0986_05F9_c2
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CEF Accounting C A
AS 100
DMZ Network
B
• Per prefix • Per adjacency • Per DMZ nexthop accounting 312 0986_05F9_c2
F AS 101 D
E AS 102
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CEF and QoS—Example Layer 3 Committed Access Rate
Distributed WFQ and/or WRED
(Token Bucket)
IP Packet Arrives
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IP Packet Departs
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CEF and QoS
• CAR classifies packets into classes • Polices within each class as “in” and “out” of profile • Mark “in” with higher precedence than “out” • Can be used to drop “out” packets 312 0986_05F9_c2
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CEF and QoS
• WRED can manage queues that develop in the routers Prioritizes “in” traffic over the rest
• WFQ can be used to allocate bandwidth to each CoS • Unused bandwidth from on CoS available for others 312 0986_05F9_c2
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CEF—BGP4 QoS • BGP advertises prefixes with AS-Path and Community attribute • Can be used to convey IP precedence to be used in forwarding to specified destinations • Allows destination-based QoS • A scalable way to prioritize incoming traffic in ingress routers 312 0986_05F9_c2
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CEF—BGP4 QoS
Service Provider ASs
Destination Source IP Precedence for this Routing Prefix
Packet Flow Data
IP
Precedence
Header
ToS Type of Service Field
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NetFlow Features
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NetFlow Applications— AS-Based Billing Global AS Customers Regional AS
Internal
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Domestic AS
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NetFlow Policy Routing (NPR) Premium ISP
E.g. ERP
Standard ISP
Application NPR
E.g.
E-Mail
NPR
FEC
Enterprise Backbone 312 0986_05F9_c2
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NetFlow Policy Routing • NetFlow calls policy routing at flow creation time • Policy routing checks if the packet needs to be policy routed • If not convey that to NetFlow • Subsequent packets for the flow don’t go through policy routing, hence minimize forwarding overhead 312 0986_05F9_c2
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NetFlow Policy Routing
• If it requires policy routing, policy route it and attach state to the flow • Subsequent packets for the flow are fast-policy routed using the attached state • Distributed version for increased performance 312 0986_05F9_c2
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NetFlow Applications
• Many flow-based applications accelerated • Encryption • Access control lists • Reverse-path forwarding checks • Resource reservation 312 0986_05F9_c2
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Tag Switching/MPLS Features
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Tag/MPLS
• Tag decouples forwarding from addressing • Allows explicit forwarding • Dynamic tunneling
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Traffic Engineering
• Increased bandwidth utilization • Useful when link not available • Handle unanticipated growth and shift in traffic • Class-of-service routing • Failure scenario 312 0986_05F9_c2
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The Overlay Solution Physical L3
L3 L2
L3
Logical
L2
L2 L2
L3
L3
L2 L3
L2
L3
L3
L3 L3
L3
L3
• Layer 2 network used to manage the bandwidth • Layer 3 sees a complete mesh • Suboptional scaling 312 0986_05F9_c2
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Traffic Engineering
• Traffic engineering requires explicit routing capability • Tag switching supports explicit routing • Tag switching along with enhanced IP routing for traffic engineering • Routing with Resource Reservation (R3) 312 0986_05F9_c2
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Traffic Engineering • Create traffic trunks Flows that are forwarded on the same path Share a common class of service
• Determine how the traffic trunks should be routed with assistance from link state protocols • Use RSVP to setup traffic trunks 312 0986_05F9_c2
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Traffic Engineering
• Maintain established routes for traffic trunks • Re-route in case of failure • Traffic assigned to trunk using IGP • Use tag learned during trunk setup to tag-switch the packets 312 0986_05F9_c2
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Traffic Engineering R9
R8
R3 R4 R2
Pop 32
R1 49 17
R6
R5
R7 22
Setup: Path (R1->R2->R6->R7->R4->R9) Reply: Resv communicates Tags and reserves bandwidth on each link 312 0986_05F9_c2
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VPN—Example VPN A/Site 2 VPN B/Site 1
10.2/16
VPN B/Site 2 10.2/16
10.1/16
VPN A/Site 3 10.3/16
10.1/16 10.4/16
VPN A/Site 1 312 0986_05F9_c2
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BGP/TAG VPN
• Constraint routing knowledge • Forwarding based on constraint knowledge • Address uniqueness • Tunneling 312 0986_05F9_c2
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BGP/TAG VPN • Constrained distribution of routing information provides control over connectivity among sites • BGP is used to carry the routing information within the backbone • BGP, RIP or static route used between site and the backbone 312 0986_05F9_c2
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Routing Information Distribution VPN A/Site 2 VPN A/Site 1 11.2/16 11.1/16 BGP
PE1
Step 3 Step 1 CEA1
Step 4
Step 2 Static
Step 5 P3
PE2
RIP
CEA2
16.1/16
16.2/16
VPN B/Site 1
VPN B/Site 2
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BGP/TAG VPN
• Along with constrained route advertisement, we need multiple forwarding table for VPN segregation • One forwarding table per VPN • Each customer port associated with a particular forwarding table 312 0986_05F9_c2
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BGP/TAG VPN • Address uniqueness within backbone achieved by creating new address family (RFC 2283) • VPN-IP address = Route distinguished + IPv4 address • New address relevant only within the backbone 312 0986_05F9_c2
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BGP/TAG VPN
• VPN identification available only in the edge • Per-hop forwarding not possible • Use tag/MPLS to forward packet using the constrained route information 312 0986_05F9_c2
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BGP/TAG VPN
Enterprise A Enterprise B
Intranet VPN 10 Extranet VPN 20 Enterprise A
Enterprise B Enterprise C 312 0986_05F9_c2
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Summary—Integrated Switching Services Layer 3 Backbones— Cisco Express Forwarding and NetFlow NetFlow Switching • Deployed at backbone periphery for network services: • Traffic accounting • QoS policy • Security
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Cisco Express Forwarding • Deployed at network core for: • Forwarding performance • Scalability • Quality of Service
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Summary—Integrated Switching Services Hybrid Layer 2 and Layer 3 Backbones— Tag and NetFlow Switching NetFlow Switching • Deployed at backbone periphery for network services: • Traffic accounting • QoS policy • Security
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Tag Switching
• Deployed on backbone for: • Virtual Private Networks • Scalability • Traffic Engineering
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Conclusion
• Different switching paths provide different benefits • Select solution based on need • Often requires hybrid switching solutions
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Please Complete Your Evaluation Form Session 312
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