Cisco IOS Advantage Webinars     A Closer Look: Comparing Benefits of EIGRP     and OSPF Webinar               Donnie Sava...
Speaker                                        Panelists                                                      Jim Guichard...
•  Submit questions in Q&A panel and send to “All Panelists”        Avoid CHAT window for better access to panelists     •...
Which Routing Protocol?Comparing Benefits of EIGRP and OSPFDonnie SavageSeptember 5th, 2012©2012 Cisco Systems Inc. All ri...
This session focuses on Internal Routing Protocol (IGP) selection and aims to answer the following    questions:          ...
Do the same design rules apply to IPv4 and IPv6?   •  Is one routing protocol better than any                             ...
The answer could be Yes If:               •  The network is complex enough to bring                      out a protocol s ...
IPv4 and IPv6 IGPs              A Comparative Overview©2012 Cisco Systems Inc. All rights reserved.   8
Does IPv6 change anything?                                                             ⁇  Are the characteristics of an IP...
OSPFv2 for IPv4                                           OSPFv3 for IPv6   OSPF                                    Distin...
• OSPF is for the most part more “optimized” (and therefore significantly more complex)                                   ...
For Your                                                                                                                  ...
Independent process from OSPFv2 – Similar concepts as OSPFv2:                                                - Runs direct...
Address Semantic Changes in LSA:                                                - Router and Network LSA carry only topolo...
OSPF Packet Format has Been Changed:                                                - The mask field has been removed from...
For Your                                                                                                                  ...
For Your                                                                                     Reference                    ...
For Your                                                                                                                  ...
For Your                                                                                                                  ...
OSPF (RFC 2328)                          OSPFv3 (RFC 5340)   Type                                                         ...
For Your                                                                                                                  ...
For Your                                                                                                                  ...
For Your                                                                                                                  ...
For Your                                                                                                                  ...
For Your                                                                                                                  ...
•  Easy to Use and Configure                 This is by far the most important reason why customers like EIGRP           ...
New TLVs used for both IPv4 and IPv6                                                     - INTERNAL_TYPE (0X0602)   Implem...
EIGRP-IPv4                                 EIGRP-IPv6   Type                                                       Distanc...
Single Process / Single        Single Process /                 Multi Process / Multi                                     ...
Tuned IPv4 OSPF, Untuned IPv6 OSPF  •  IPv6 IGP impact on the IPv4 IGP         convergence                                ...
•  The similarities between the IPv4 and IPv6 IGP lead to similar network design                      considerations as fa...
For Your                                                Reference              EIGRP – OSPF Overview              Features...
For Your                                                                                         Reference                ...
For Your                                                                                     Reference                    ...
For Your                                                                                           Reference              ...
For Your                                                                                                 Reference        ...
Convergence Speed©2012 Cisco Systems Inc. All rights reserved.   37
•  Which protocol converges faster?•  IS-IS versus OSPF verses EIGRP          IS-IS and OSPF have the same characteristics...
•  Five steps to convergence          1.  Detect the failure          2.  Calculate new routes around the topology change ...
A               •  Start with B>C>E and B>D>E being equal                  B                      cost               •  If...
A                                                                                     SPF               •  Start with B>C>...
•  Within a single flooding domain          A single area in OSPF          A single flooding domain in IS-IS•  Convergence...
A               •  E floods topology changes to C and D                   Area 2               •  C and D summarize these ...
•  Between flooding domains, link state protocols have distance vector                      characteristics               ...
For Your                                                                                                    Reference     ...
Tuned IPv4 OSPF, Untuned IPv6 OSPF  •  Convergence time with default timers and                                           ...
•  Within a flooding domain                           The average convergence time, with default timers, is going to be   ...
A•  EIGRP converges Equal Cost paths similar to Link State;          If C fails, B and E can shift from sharing traffic be...
•  DUAL works on a simple geometric principle:                           If my neighbor s cost to reach a given destinatio...
•  B will install the path through C, and mark the path                      through D as a feasible successor            ...
•  If the second path cannot be proven loop free                                                                          ...
•  For paths with feasible successors, convergence time is in the milliseconds                   The existence of feasible...
IPv4 IGP Convergence Data         •  EIGRP with feasible successors                                                       ...
•  “The goal of IP Fast-Reroute is to reduce failure reaction time to 10s of milliseconds by using     a pre-computed alte...
  IP-FRR is a mechanism that reduces traffic disruption to 10s of milliseconds in event of      link or node failure  A ...
•  Per-prefix LFA FRR enabled for all areas unless explicitly specified•  IP-FRR automatically enabled on OSPF interfaces•...
•  Uses existing Feasible Successors, so no     additional computational load                                router eigrp ...
•  It s possible to converge in under one second using any protocol,                      with the right network design   ...
Design and Topology Considerations©2012 Cisco Systems Inc. All rights reserved.      59
For Your                                                    Reference                     •  State Full Mesh              ...
•  Full mesh topologies are complex:                   2 routers = 1 link                           3 routers = 3 links   ...
•  Flooding routing information through a full mesh          topology is also complicated   •  Each router will, with opti...
•  OSPF and IS-IS can both use mesh groups to          reduce the flooding in a full mesh network    •  Mesh groups are ma...
Summarize   •  Routes must be advertised between every pair          of peers in the mesh so each router has the          ...
Use ip ospf database-filter all out to manually designate flooding points and increase scaling through   OSPF             ...
•  OSPF has a hard edge at flooding         domain borders   •  Summarization and filtering can occur                     ...
•  In a three layer hierarchy, the decision of          where to place the area border is more      High Degree           ...
For Your                                                                             Reference   •  IS-IS has a hard edge ...
For Your                                                                                  Reference    •  In a three layer...
•  The depth of the hierarchy doesn’t alter the way          EIGRP is deployed; there are no hard edges         High Degre...
EIGRP chooses the metric of the lowest cost                                                                               ...
CSCed01736  •  Could use loopback interface to force the metric to                                                        ...
CSCed01736    •  We would like C to be able to receive as few          routes as possible                                 ...
CSCed01736    •  The simplest way to handle this is to configure a          leak list on the summary route                ...
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)
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A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)

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Presentation compares the benefits of Enhanced Interior Gateway Routing Protocol (EIGRP) and Open Shortest Path First (OSPF). The slides cover OSPF (link state) and EIGRP (DUAL) routing protocols comparing and contesting a number of considerations, such as convergence speed and network design and topology. We will also delve into how each handles the co-existence of IPv4 and IPv6.

This session aims to answer the following questions:
- Which routing protocol should I use in my network?
- Should I switch from the one I'm currently using?
- Do the same selection rules apply to IPv4 and IPv6?
- How will my IPv4 and IPv6 routing protocols coexist?

Replay the WebEx recording: https://cisco.webex.com/ciscosales/lsr.php?AT=pb&SP=EC&rID=62988787&rKey=a54e8b6408ee9733

Learn more about upcoming TechAdvantage (formerly IOS Advantage) sessions at: http://www.cisco.com/go/iosadvantage

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A Closer Look: Comparing Benefits of EIGRP and OSPF (IOS Advantage Webinar)

  1. 1. Cisco IOS Advantage Webinars A Closer Look: Comparing Benefits of EIGRP and OSPF Webinar Donnie Savage We’ll get started a few minutes past the top of the hour. Note: you may not hear any audio until we get started.© 2012 Cisco and/or its affiliates. All rights reserved. 1
  2. 2. Speaker Panelists Jim Guichard Chris Le Principle Engineer Engineering Product Manager jguichar@cisco.com Engineering cle@cisco.com Saul Adler Anton Smirnov Technical Leader Engineering Technical Leader Donnie Savage Technical Leader sadler@cisco.com Engineering asmirnov@cisco.com Technical Marketing dsavage@cisco.com©2012 Cisco Systems Inc. All rights reserved. 2
  3. 3. •  Submit questions in Q&A panel and send to “All Panelists” Avoid CHAT window for better access to panelists •  For Webex audio, select COMMUNICATE > Join Audio Broadcast •  For Webex call back, click ALLOW phone button at the bottom of participants side panel •  Where can I get the presentation? Or send email to: ask_iosadvantage@cisco.com •  Please complete the post-event survey •  Join us October 3rd for our next IOS Advantage Webinar: Using LISP to Solve Todays IP Host Mobility Challenges www.cisco.com/go/iosadvantage •  Follow us @GetYourBuildOn©2012 Cisco Systems Inc. All rights reserved. 3
  4. 4. Which Routing Protocol?Comparing Benefits of EIGRP and OSPFDonnie SavageSeptember 5th, 2012©2012 Cisco Systems Inc. All rights reserved. 4
  5. 5. This session focuses on Internal Routing Protocol (IGP) selection and aims to answer the following questions: ⁇  - Is one protocol better than the others? ⁇  - Which routing protocol should I use in my network? ⁇  - Should I switch from the one I’m using? ⁇  - What are the IPv6 counterparts of the most used IPv4 IGPs and where are they similar or differ? ⁇  - Do the same selection rules apply to IPv4 and IPv6? ⁇  - How will my IPv4 and IPv6 routing protocols coexist? The session will compare DUAL (EIGRP) and Link State (OSPF) routing protocols applying a number of considerations, such as convergence speed and network design and topology. Additionally, it will provide an overview of the IPv6 counterparts of the most used IPv4 IGPs and discuss the similarities and differences between the “twin” routing protocols. Finally, the co-existence of IPv4 and IPv6 routing protocols will also be discussed.   As a pre-requisite for this session, attendees should have a reasonable understanding of EIGRP, IS-IS, OSPF, IPv4, and IPv6 routing protocol design and operation.©2012 Cisco Systems Inc. All rights reserved. 5
  6. 6. Do the same design rules apply to IPv4 and IPv6? •  Is one routing protocol better than any What you Like? other protocol? Which protocol uses less resources? •  Depends on how you define Better! Easier to configure? What are the IPv6 counterparts of the most used IPv4 IGPs and where are they similar or differ? Which protocol converges faster? How will my IPv4 and IPv6 routing protocols coexist? Degrades more gracefully? Scales to a larger number of routers, routes, or neighbors? More flexible? Easier to troubleshoot?©2012 Cisco Systems Inc. All rights reserved. 6
  7. 7. The answer could be Yes If: •  The network is complex enough to bring out a protocol s specific advantages •  You can define a specific feature (or set of features) that will benefit your network tremendously… But then again, the answer might be No! •  Every protocol has some features and not others, different scaling properties, etc. •  Let’s consider some specific topics for each protocol…©2012 Cisco Systems Inc. All rights reserved. 7
  8. 8. IPv4 and IPv6 IGPs A Comparative Overview©2012 Cisco Systems Inc. All rights reserved. 8
  9. 9. Does IPv6 change anything? ⁇  Are the characteristics of an IPv6 IGP similar or different from an IPv4 IGP? •  Most likely the IPv6 IGP will not be deployed in a brand new network and just by itself ⁇  What is the impact on the convergence of IPv4? •  Most likely the existing IPv4 services are more important at first since they are generating ⁇  How are the resources shared between most of the revenue the two protocols? ⁇  Are the topologies going to be congruent? ⁇  How easy is it to manage parallel IPv4 / IPv6 environments? ⁇  Opportunity to adopt a new IGP for IPv6?©2012 Cisco Systems Inc. All rights reserved. 9
  10. 10. OSPFv2 for IPv4 OSPFv3 for IPv6 OSPF Distinct but similar protocols with OSPFv3 being a cleaner implementation that takes advantage of IPv6 specificities Extended to support IPv6 IS-IS Natural fit to some of the IPv6 foundational concepts Support Single and Multi Topology operation Extended to support IPv6 EIGRP Natural fit to some of the IPv6 foundational concepts Some changes reflecting IPv6 characteristics   For all intents and purposes, the IPv6 IGPs are very similar to their IPv4 counterparts   IPv6 IGPs have additional features that could lead to new designs©2012 Cisco Systems Inc. All rights reserved. 10
  11. 11. • OSPF is for the most part more “optimized” (and therefore significantly more complex) • Only LSAs are extensible (not hellos, etc.). • Unrecognized LSA types are not flooded (though opaque LSAs can suffice, if implemented High-level perspective universally). • Uses complex, multistate process to synchronize databases between neighbors. Intended to minimize transient routing problems by ensuring that a newborn router has nearly complete routing information before it begins carrying traffic. OSPF runs on top of IP • Traditional IP routing protocol approach Encapsulation • Allows virtual links (if you need them) • Relies on IP fragmentation for large LSAs • Subject to spoofing and DoS attacks (use of authentication is strongly advised).©2012 Cisco Systems Inc. All rights reserved. 11
  12. 12. For Your Reference • LSAs are mostly numerous and small (one external per LSA, one summary per LSA). • Network and router LSAs can become large. Database Node • LSAs are grouped into LS Updates during flooding. • LS Updates are built individually at each hop. • Small changes can yield small packets (but router, network LSAs can be large). • An OSPF link can be only in one area, and routers must agree on the area ID. Links and Areas • Area borders cross routers in OSPF.©2012 Cisco Systems Inc. All rights reserved. 12
  13. 13. Independent process from OSPFv2 – Similar concepts as OSPFv2: - Runs directly over IPv6 (port 89) - Uses the same basic packet types Implementation - Neighbor discovery and adjacency formation mechanisms are identical (All OSPF Routers FF02::5, All OSPF DRs FF02::6) - LSA flooding and aging mechanisms are identical - Same interface types (P2P, P2MP, Broadcast, NBMA, Virtual) OSPFv3 Is Running per Link Instead of per Node (and IP Subnet) Support of Multiple Instances per Link: - New field in OSPF packet header allows running multiple instances per link - Instance ID should match before packet is being accepted Important Differences - Useful for traffic separation, multiple areas per link Generalization of Flooding Scope: - Three flooding scopes for LSAs (link-local scope, area scope, AS scope) and they are coded in the LS type explicitly©2012 Cisco Systems Inc. All rights reserved. 13
  14. 14. Address Semantic Changes in LSA: - Router and Network LSA carry only topology information - Router LSA can be split across multiple LSAs; Link State ID in LSA header is a fragment ID - Intra area prefixes are carried in a new LSA payload called intra-area-prefix-LSAs - Prefixes are carried in the payload of inter-area and external LSA Important Explicit Handling of Unknown LSA: Differences - The handling of unknown LSA is coded via U-bit in LS type (cont.) - When U bit is set, the LSA is flooded within the corresponding flooding scope, as if it was understood - When U bit is not set, the LSA is flooded within the link local scope Authentication Is Removed from OSPF: - Authentication in OSPFv3 has been removed and OSPFv3 relies now on IPv6 authentication header since OSPFv3 runs over IPv6 - Autype and Authentication field in the OSPF packet header therefore have been suppressed©2012 Cisco Systems Inc. All rights reserved. 14
  15. 15. OSPF Packet Format has Been Changed: - The mask field has been removed from Hello packet - IPv6 prefix are only present in payload of Link State update packet Important Two New LSAs Have Been Introduced: Differences - Link-LSA has a link local flooding scope and has three purposes Carry IPv6 link local address used for NH calculation (cont.) Advertise IPv6 global address to other routers on the link (used for multi-access link) Convey router options to DR on the link - Intra-area-prefix-LSA to advertise router s IPv6 address within the area Standardization Main standard: RFC 2740 Notes Evolution: draft-ietf-ospf-mt-ospfv3 draft-ietf-ospfv3-af-alt©2012 Cisco Systems Inc. All rights reserved. 15
  16. 16. For Your Reference Internal Internal •  Areas: the tool to make OSPF Scale! •  OSPF uses a 2 level hierarchical model •  One SPF per area, flooding Area 12 done per area ABR •  Regular, Stub, Totally Stubby and NSSA Area 10 ABR Area Types ABR Backbone Area 0 •  A router has a separate LS database for each area to which it belongs •  All routers belonging to the same area ABR should have identical databases Area 11 •  SPF calculation is performed independently for each area ASBR •  LSA flooding is bounded by area RIP/RIPv2 Internal World©2012 Cisco Systems Inc. All rights reserved. 16
  17. 17. For Your Reference LSA Function Code LSA Type Router-LSA 1 0x2001 Network-LSA 2 0x2002 Inter-Area-Prefix-LSA 3 0x2003 Inter-Area-Router-LSA 4 0x2004 AS-External-LSA 5 0x4005 Group-membership-LSA 6 0x2006 Type-7-LSA 7 0x2007 Link-LSA 8 0x0008 New Intra-Area-Prefix-LSA 9 0x2009©2012 Cisco Systems Inc. All rights reserved. 17
  18. 18. For Your Reference Internal Internal Network changes generates link-state Type3 advertisements (LSA) •  Router LSA (Type 1) ABR Area 12 •  Network LSA (Type 2) Area 10 •  Summary LSA (type 3 and type 4) ABR •  External LSA (type 5) ABR Backbone •  All routers exchange LSAs to build and Area 0 maintain a consistent database •  The protocol remains relatively quiet ABR during steady-state conditions •  Periodic refresh of LSAs every 30 Area 11 minutes •  Otherwise, updates only sent when there ASBR are changes Type4/5 RIP/RIPv2 Internal World©2012 Cisco Systems Inc. All rights reserved. 18
  19. 19. For Your Reference Internal •  LSA flooded throughout the area in response to any topology change Internal •  SPF runs in every router on the receipt of any LSA indicating a topology change •  OSPF by design has a number of throttling ABR Area 12 mechanisms to prevent the network from thrashing during periods of instability Area 10 ABR ABR Backbone •  Full SPF Area 0 -  Triggered by the change in Router or Network LSA ABR -  All LSA types are processed Area 11 •  Partial SPF -  Triggered by the change in Type-3/4/5/7 LSA ASBR -  Part of the LSAs are processed (see slide notes) RIP/RIPv2 Internal World©2012 Cisco Systems Inc. All rights reserved. 19
  20. 20. OSPF (RFC 2328) OSPFv3 (RFC 5340) Type Link state Link state Metric Cost (1-65535) Cost (1-65535) Loop prevention Dijkstra Dijkstra Administrative distance 110 110 L3 transport S/D IPv4 unicast / 224.0.0.5 IPv6 LL unicast / FF02::5 IPv4 unicast / 224.0.0.6 IPv6 LL unicast / FF02::6 L4 transport IP 89 Next Header 89 !" ipv6 unicast-routing" !" !" interface Loopback0" interface Loopback0" ip address 10.10.0.1 255.255.255.255" ipv6 address 2001:DB8:1000::1/128" !" ipv6 ospf 1 area 0 instance 11" !" !" interface Ethernet0/0" interface Ethernet0/0" ip address 10.0.0.1 255.255.255.0" ipv6 address 2001:DB8::1/64" !" ipv6 ospf 1 area 0 instance 11" !" !" router ospf 1" ipv6 router ospf 1" network 10.0.0.0 0.255.255.255 area 0" router-id 10.10.10.1" passive-interface loopback0" passive-interface loopback0"©2012 Cisco Systems Inc. All rights reserved. 20
  21. 21. For Your Reference Two new TLVs: - IPv6 Reachability TLV (0xEC): Describes network reachability (IPv6 routing prefix, metric information and option bits) - IPv6 Interface Address TLV (0xE8): Contains 128 bit address. Implementation Hello PDUs, must contain the link-local address but for LSP, must only contain the non link-local address) A new Network Layer Protocol Identifier (NLPID): Allows IS-IS routers to advertise IPv6 prefix payload using 0x8E value Single Topology (default for all protocols supported) - potentially beneficial in saving resources (same topology and same SPF) Operating Multi Topology (draft-ietf-isis-wg-multi-topology) - Independent IPv4 and IPv6 topologies, Considerations independent interface metrics Transition mode available - both types of TLVs are advertised Standardization: draft-ietf-isis-ipv6-07 Notes Evolution: draft-ietf-isis-mi©2012 Cisco Systems Inc. All rights reserved. 21
  22. 22. For Your Reference • IS-IS was not designed from the start as an IP routing protocol. • Adjacency is reported once two-way connectivity has been ensured. High-level perspective • IS-IS essentially uses its regular flooding techniques to synchronize neighbors. • Transient routing issues can be reduced (albeit non-deterministically) by judicious use of the “overload” bit. IS-IS runs directly over L2 (next to IP) • Sort of makes sense (since it was designed for CLNS) Encapsulation • Does not require a valid interface address to transmit protocol messages. • Agnostic about the type of prefix being transported. • Partition repair requires tunneling (rarely implemented).©2012 Cisco Systems Inc. All rights reserved. 22
  23. 23. For Your Reference IS-IS database node is an Link State Packet (LSP) • LSPs are clumps of topology information organized by the originating router • Always flooded intact, unchanged across all flooding hops (so LSP MTU is an architectural Database Node constant—it must fit across all links) • Small topology changes always yield entire LSPs (though packet size turns out to be much less of an issue than packet count) • Implementations can attempt clever packing • In IS-IS, if routers do not agree on the area ID, they form L2 adjacency. Links and Areas • Area borders cross links in IS-IS. • In IS-IS, a link can be associated with an L1 and an L2 area simultaneously.©2012 Cisco Systems Inc. All rights reserved. 23
  24. 24. For Your Reference Two new TLVs: - IPv6 Reachability TLV (0xEC): Describes network reachability (IPv6 routing prefix, metric information and option bits) Implementation - IPv6 Interface Address TLV (0xE8): Contains 128 bit address. Hello PDUs, must contain the link-local address but for LSP, must only contain the non link-local address A new Network Layer Protocol Identifier (NLPID): Allows IS-IS routers to advertise IPv6 prefix payload using 0x8E value (IPv4: 0xCC). Carried in Protocols Supported TLV (0x81). Single Topology (default for all protocols supported) - potentially beneficial in saving resources (same topology and same SPF) Operational Multi Topology (RFC 5120) - Independent IPv4 and IPv6 topologies (MT ID 0,2), Considerations independent interface metrics. Wide metrics. New TLVs! Transition mode available - both types of TLVs are advertised Single Topology: http://tools.ietf.org/html/rfc5308 Notes Multi Topology: http://tools.ietf.org/html/rfc5120 Evolution – Multi Instance: http://tools.ietf.org/html/draft-ietf-isis-mi-05©2012 Cisco Systems Inc. All rights reserved. 24
  25. 25. For Your Reference IS-IS for IPv4 (RFC 1195) IS-IS for IPv6 (RFC 5308) Type Link state Link state Metric (Narrow / Wide) Cost (1-63 / 16777214) Cost (1-63 / 16777214) Loop prevention Dijkstra Dijkstra Administrative distance 115 115 L3 / L4 transport CLNS CLNS!" ipv6 unicast-routing" ipv6 unicast-routing"!" !" !"interface Loopback0" interface Loopback0" interface Ethernet0/0" ip address 10.10.0.1 255.255.255.255" ipv6 address 2001:DB8:1000::1/128" ipv6 address 2001:DB8:1000::1/128" ip router isis CISCO" ipv6 router isis CISCO" ipv6 router isis CISCO" isis circuit-type level-1" isis circuit-type level-1" isis circuit-type level-1" isis metric 10000" isis ipv6 metric 10000" isis ipv6 metric 10000"!" !" !"interface Ethernet0/0" interface Ethernet0/0" router isis CISCO" ip address 10.0.0.1 255.255.255.0" ipv6 address 2001:DB8::1/64" net 49.0001.2222.2222.2222.00" ip router isis CISCO" ipv6 router isis CISCO" metric-style wide" isis circuit-type level-1" isis circuit-type level-1" log-adjacency-changes all" isis metric 10000" isis ipv6 metric 10000" !"!" !" address-family ipv6"router isis CISCO" router isis CISCO" multi-topology" net 49.0001.1111.1111.1111.00" net 49.0001.1111.1111.1111.00" exit-address-family" metric-style wide" metric-style wide" log-adjacency-changes all" log-adjacency-changes all"!" ©2012 Cisco Systems Inc. All rights reserved. 25
  26. 26. •  Easy to Use and Configure  This is by far the most important reason why customers like EIGRP •  Easy to Understand  Simple to learn and deploy as compared to other major IGPs •  Scalable Functionality  Suitable for deployment in multiple scenarios (hub and spoke, broadcast etc) •  Sub-Second Convergence from inception  Backup routes are pre-computed and instantaneously used in case of failure •  High Availability & Reliability  Provides comprehensive support for High Availability and simplicity improves reliability •  Proven Deployment  The most widely deployed enterprise routing protocol  Widely available across Cisco platforms suitable for Enterprise & Commercial©2012 Cisco Systems Inc. All rights reserved. 26
  27. 27. New TLVs used for both IPv4 and IPv6 - INTERNAL_TYPE (0X0602) Implementation - EXTERNAL_TYPE (0X0603) Same Metrics used by IPv6 and IPv4 Hellos are sourced from the link-local address and destined to FF02::A (all EIGRP routers); this means that neighbors do not have to share the same global prefix (with the exception of explicitly specified neighbors where traffic is unicasted) Important Auto (classful) summarization disabled by default (For IPv6 and current IPv4) Differences No split-horizon in the case of EIGRP for IPv6 (because IPv6 supports multiple prefixes per interface) RouterID which must be explicitly configured if no IPv4 address Notes Its just like EIGRP-IPv4 except where its different©2012 Cisco Systems Inc. All rights reserved. 27
  28. 28. EIGRP-IPv4 EIGRP-IPv6 Type Distance vector Distance vector Metric Vector Metrics Vector Metrics Loop prevention DUAL, split horizon DUAL, split horizon Admin distance 5 (sum.), 90 (int.), 170 (ext.) 5 (sum.), 90 (int.), 170 (ext.) L3 transport S/D IPv4 unicast / 224.0.0.10 IPv6 LL unicast / FF02::A L4 transport IP 88, RTP (reliable multicast) Next Header 88, RTP !" ipv6 unicast-routing" !" !" interface Loopback0" interface Loopback0" ip address 10.10.0.1 255.255.255.255" ipv6 address 2001:DB8:1000::1/128" !" !" interface Ethernet0/0" interface Ethernet0/0" ip address 10.0.0.1 255.255.255.0" ipv6 address 2001:DB8::1/64" !" !" router eigrp CSCO" router eigrp CSCO" address-family ipv4 autonomous-system 4453" address-family ipv6 autonomous-system 4453" af-interface Loopback0" router-id 10.10.10.1" passive-interface" af-interface Loopback0" topology base" passive-interface" " topology base"©2012 Cisco Systems Inc. All rights reserved. 28
  29. 29. Single Process / Single Single Process / Multi Process / Multi Topology Multi Topology Topology Protocols IS-IS ST IS-IS MT OSPFv2 + OSPFv3 EIGRP-IPv4 + EIGRP-IPv6 IP topologies Single (IPv4+IPv6) Multiple Multiple Congruent Non-congruent Non-congruent Flooding + Router/ Common Common Multiple protocol instances on network resources given link Dual/SPF Single Multiple Multiple Topology/LS Single Single Multiple databases Large Large Control plane Common More separation Clear separation Less resource intensive Protocol-specific optimization Protocol-specific optimization More deterministic IPv4/IPv6 possible possible co-existence More resource intensive More resource intensive©2012 Cisco Systems Inc. All rights reserved. 29
  30. 30. Tuned IPv4 OSPF, Untuned IPv6 OSPF •  IPv6 IGP impact on the IPv4 IGP convergence 0.5 0.45 0.4 0.35 •  Aggressive timers on both IGPs IPv4 OSPF 0.3 Time 0.25 highlight competition for resources 0.2 IPv4 OSPF w/ IPv6 OSPF 0.15 0.1 Linear (IPv4 0.05 OSPF w/ IPv6 0 OSPF) Linear (IPv4 0 500 1000 1500 2000 2500 3000 OSPF) Number of Prefixes Tuned IPv4 ISIS, Tuned IPv6 ISIS Tuned IPv4 OSPF, Tuned IPv6 OSPF 0.6 0.7 0.5 0.6 0.5 IPv4 OSPF 0.4 IPv4 ISIS 0.4 Time Time 0.3 IPv4 ISIS w/ 0.3 IPv4 OSPF w/ 0.2 IPv6 ISIS IPv6 OSPF 0.2 0.1 Linear (IPv4 Linear (IPv4 0.1 ISIS w/ IPv6 OSPF w/ IPv6 0 ISIS) 0 OSPF) Linear (IPv4 Linear (IPv4 0 500 1000 1500 2000 2500 3000 ISIS) 0 500 1000 1500 2000 2500 3000 OSPF) Number of Prefixes Number of Prefixes©2012 Cisco Systems Inc. All rights reserved. 30
  31. 31. •  The similarities between the IPv4 and IPv6 IGP lead to similar network design considerations as far as routing is concerned—For the rest of the presentation, the analysis is IP version AGNOSTIC! IPv6 specific considerations are noted where relevant •  The implementation of the IPv6 IGPs achieves parity with the IPv4 counterparts in most aspects but this is an ongoing development and optimization process •  Coexistence of IPv4 and IPv6 IGPs is a very important design consideration.©2012 Cisco Systems Inc. All rights reserved. 31
  32. 32. For Your Reference EIGRP – OSPF Overview Features at a Glance©2012 Cisco Systems Inc. All rights reserved. 32
  33. 33. For Your Reference IOS-XE IOS-XR NX-OS BFD Yes Roadmap Yes IP Fast Reroute 3.7 Roadmap Roadmap Non-Stop Routing 3.9 Roadmap Roadmap UCMP Yes Yes No EIGRP add-path 3.8 Roadmap Roadmap VRF-Aware EIGRP Yes Yes Yes EIGRP PE/CE Yes Yes Yes EIGRP 6PE/6VPE 3.9 Roadmap Roadmap©2012 Cisco Systems Inc. All rights reserved. 33
  34. 34. For Your Reference IOS-XE IOS-XR NX-OS EIGRP IPv4/IPv6 MIB Yes/3.7 No/No Yes/No Route Tag Enhancement Yes No Yes EIGRP Multi-Instance Yes No Yes EIGRP Prefix Limit Yes Yes Yes EIGRP Route Authentication Yes Yes Yes EIGRP HMAC-SHA-256 Authentication Yes No No EIGRP Wide Metrics Yes Yes Yes©2012 Cisco Systems Inc. All rights reserved. 34
  35. 35. For Your Reference EIGRP OSPF Common Configuration Yes No Sub-second Convergence Yes IPFRR Sends partial routing updates (advertise only new/changed information) Yes Yes Floods database periodically No Yes Supports manual summarization Yes Yes Allows manual summarization at any router Yes No Sends routing information using IPv4/IPv6 multicast on LANs Yes Yes Uses the concept of a designated router on a LAN No Yes Flexible network design with no need to create areas Yes No Supports STUB networks 3500* 600 Supports both equal and unequal cost load balancing Yes No Robust metric based on interface characteristics Yes No Public standard No Yes©2012 Cisco Systems Inc. All rights reserved. 35
  36. 36. For Your Reference EIGRP OSPF Interfaces must be in an up/up state Yes Yes Interfaces must be in the same subnet Yes Yes Must pass neighbor authentication (if configured) Yes Yes Must use the same AS/Process-ID Yes No Hello and hold/dead timers must match No Yes IP MTU must match No Yes Router IDs must be unique No* Yes K-values must match Yes N/A Must be in the same area N/A Yes * Duplicate EIGRP RIDs does not prevent neighbors forming, but EIGRP will reject routes with matching RID©2012 Cisco Systems Inc. All rights reserved. 36
  37. 37. Convergence Speed©2012 Cisco Systems Inc. All rights reserved. 37
  38. 38. •  Which protocol converges faster?•  IS-IS versus OSPF verses EIGRP IS-IS and OSPF have the same characteristics, from a high level, so we will consider them both as link state Is DUAL faster, or Dijkstra?•  Rules of Thumb The more routers involved in convergence, the slower convergence will be The more routes involved in convergence, the slower convergence will be©2012 Cisco Systems Inc. All rights reserved. 38
  39. 39. •  Five steps to convergence 1.  Detect the failure 2.  Calculate new routes around the topology change 3.  Flood the failure/repair information 4.  Add changed routing information to the routing table (RIB) 5.  Update the FIB (possibly distributed)•  Steps 1-4-5 are similar for any routing protocol, so we’ll only look at steps 2-3•  But, it’s important to keep in mind steps 1-4-5, since they often impact convergence more than the routing protocol does©2012 Cisco Systems Inc. All rights reserved. 39
  40. 40. A •  Start with B>C>E and B>D>E being equal B cost •  If C fails, B and E can shift from sharing traffic between C and D to sending traffic to C D D only •  Number of routers involved in convergence: 2 (B and E) E •  Convergence time is in the milliseconds F©2012 Cisco Systems Inc. All rights reserved. 40
  41. 41. A SPF •  Start with B>C>F and B>D>E>F B •  C fails •  B and F flood new topology information D C •  All routers have to run SPF to calculate new path through the network; E •  B and F change their routing tables to reflect the SPF F changed topology •  Number of routers involved in convergence: 2 (B and F) ; maybe D and E as well G©2012 Cisco Systems Inc. All rights reserved. 41
  42. 42. •  Within a single flooding domain A single area in OSPF A single flooding domain in IS-IS•  Convergence time depends on; Flooding timers, SPF timers, Number of nodes/leaves in the SPF tree•  What happens when we cross a flooding domain boundary?©2012 Cisco Systems Inc. All rights reserved. 42
  43. 43. A •  E floods topology changes to C and D Area 2 •  C and D summarize these topology changes B (removing the topology information), and flood it to B Area 0 •  B builds a summary from the summary C D flooded to B, and floods it into area 2 •  A calculates a route to B, then recurses C onto E E Area 1 F©2012 Cisco Systems Inc. All rights reserved. 43
  44. 44. •  Between flooding domains, link state protocols have distance vector characteristics •  This can have negative or positive impacts on convergence time in a large network Reduces tree size Allows partial SPFs, rather than full SPFs Introduces translation and processing at the flooding domain boundaries •  The impact is primarily dependent on the network design©2012 Cisco Systems Inc. All rights reserved. 44
  45. 45. For Your Reference OSPF •  IS-IS •  Carrier Delays •  Carrier Delays •  Hello/dead timers (fast hellos) •  Hello/dead timers (fast hellos) •  Bidirectional Forwarding Detection(BFD) •  Bidirectional Forwarding Detection (BFD) •  LSA packet pacing •  LSP pacing •  Interface event dampening •  Interface event dampening •  Exponential throttle timers for LSP & SPF •  Exponential throttle timers for LSA & SPF •  PRC interval •  MinLSArrivalInterval •  Incremental SPF •  Incremental SPF©2012 Cisco Systems Inc. All rights reserved. 45
  46. 46. Tuned IPv4 OSPF, Untuned IPv6 OSPF •  Convergence time with default timers and 2.500 tuned timers 2.000 •  IPv4 and IPv6 IGP convergence times are 1.500 IPv4 OSPF Time IPv6 OSPF similar 1.000 Linear (IPv4 OSPF) The IPv6 IGP implementations might not be fully 0.500 Linear (IPv6 OSPF) optimized yet 0.000 0 500 1000 1500 2000 2500 3000 Not all Fast Convergence optimizations might be Number of Prefixes available Tuned IPv4 ISIS, Tuned IPv6 ISIS Tuned IPv4 OSPF, Tuned IPv6 OSPF 0.45 0.5 0.4 0.45 0.35 0.4 IPv4 ISIS 0.35 IPv4 OSPF 0.3 0.3 0.25 Time Time IPv6 ISIS 0.25 IPv6 OSPF 0.2 Linear (IPv6 0.2 Linear (IPv6 0.15 0.15 ISIS) OSPF) 0.1 Linear (IPv4 0.1 Linear (IPv4 0.05 ISIS) 0.05 OSPF) 0 0 0 500 1000 1500 2000 2500 3000 0 500 1000 1500 2000 2500 3000 Number of Prefixes Number of Prefixes©2012 Cisco Systems Inc. All rights reserved. 46
  47. 47. •  Within a flooding domain The average convergence time, with default timers, is going to be around 3 to 7 seconds With fast timers, the convergence time can be in the milliseconds There are operational 200 node IS-IS and OSPF networks with 500 millisecond convergence times •  Outside the flooding domain Network design and route aggregation are the primary determining factors of convergence speed©2012 Cisco Systems Inc. All rights reserved. 47
  48. 48. A•  EIGRP converges Equal Cost paths similar to Link State; If C fails, B and E can shift from sharing traffic between B C and D to sending traffic to D only•  EIGRP converges Unequal Cost different from Link State depending on wheather it has a “Feasible Successor” or C D not•  To understand how a “Feasible Successor” is selected, we need to understand how DUAL handles path cost… E F©2012 Cisco Systems Inc. All rights reserved. 48
  49. 49. •  DUAL works on a simple geometric principle: If my neighbor s cost to reach a given destination is less A than my best cost, then the alternate path cannot be a 10 loop 30 35 B •  When B calculates the cost to F; 10 15 •  B>C>E>F is 30 C D •  B>D>E>F is 35 10 10 •  B’s Neighbor D reports its cost as; D>E>F is 20 20 E •  This is which is less than the best path, 30, so 10 B>D>E>F cannot be a loop F©2012 Cisco Systems Inc. All rights reserved. 49
  50. 50. •  B will install the path through C, and mark the path through D as a feasible successor A •  When C fails, B looks for alternate loop free paths 10 B •  Finding one, it installs it 10 15 •  Convergence time is in the milliseconds •  Number of routers involved in convergence: C D 2 (B and E) 10 10 E 10 F©2012 Cisco Systems Inc. All rights reserved. 50
  51. 51. •  If the second path cannot be proven loop free A •  B and E detect the failure, and have no alternate path B •  B queries A and D for alternate path to F A replies that it has no path D replies with its path C D •  E queries D and F for alternate path to A F replies that it has no path D replies with its path E F©2012 Cisco Systems Inc. All rights reserved. 51
  52. 52. •  For paths with feasible successors, convergence time is in the milliseconds The existence of feasible successors is dependent on the network design •  For paths without feasible successors, convergence time is dependent on the number of routers that have to handle and reply to the query Queries are blocked one hop beyond aggregation and route filters Query range is dependent on network design •  Good design is the key to fast convergence in an EIGRP network©2012 Cisco Systems Inc. All rights reserved. 52
  53. 53. IPv4 IGP Convergence Data •  EIGRP with feasible successors 7000 •  IS-IS with tuned timers 6000 •  OSPF with tuned timers 5000 •  EIGRP without feasible successors Milliseconds 4000 •  OSPF with default timers •  IS-IS with default timers 3000 Route 2000 •  We can sort typical convergence Generator times into three groups A 1000 0 5000 4000 1000 2000 3000 B C D Routes©2012 Cisco Systems Inc. All rights reserved. 53
  54. 54. •  “The goal of IP Fast-Reroute is to reduce failure reaction time to 10s of milliseconds by using a pre-computed alternate next-hop, in the event that the currently selected primary next- hop fails, so that the alternate can be rapidly used when the failure is detected.” -draft-ietf-rtgwg- ipfrr-spec-base-12•  Protecting Node, also referred as “Calculating Node”, is responsible for pre-computing an alternate next-hop in event currently selected primary next-hop fails so alternate can be rapidly used when link/node failure is detected•  Alternative Next-Hop is not aware of link failure and operates on assumption it is still up Protecting Node Primary Next-Hop A B Primary Path Repair Path C©2012 Cisco Systems Inc. All rights reserved. 54
  55. 55.   IP-FRR is a mechanism that reduces traffic disruption to 10s of milliseconds in event of link or node failure  A failure is locally repaired by router next to failure before routers in network re- converge around such failure  IOS implements *per-prefix Loop Free Alterative FRR  But….. ✗  It runs at the process level ✗  Does not guarantee time limit ✗  Performance depends on tuning and platform implementation   IPv4 Only – IPv6 planned©2012 Cisco Systems Inc. All rights reserved. 55
  56. 56. •  Per-prefix LFA FRR enabled for all areas unless explicitly specified•  IP-FRR automatically enabled on OSPF interfaces•  No audit trail of potential LFAs is stored•  Repair paths are computed for all prefixes though not all prefixes may have repair paths router ospf 1" router-id 10.1.1.1" fast-reroute per-prefix enable prefix-priority low" Protecting Node network 10.0.0.0 255.255.0.0 area 0" …" A©2012 Cisco Systems Inc. All rights reserved. 56
  57. 57. •  Uses existing Feasible Successors, so no additional computational load router eigrp CISCO" address-family ipv4 autonomous-system 4453
•  Automatically enabled on all EIGRP network 10.0.0.0 255.255.0.0
 interfaces covered by network statement topology base
•  Per-prefix LFA FRR enabled via route- fast-reroute tie-break <attribute> <priority>" fast-reroute per-prefix all | route-map <map-name>
 maps …"•  Repair paths can be equal or unequal cost (thought variance command)•  Repair paths are computed for all prefixes RTR-A#sh eigrp add ipv4 topology frr" though not all prefixes may have a FS EIGRP-IPv4 Topology Table for AS(1)/ID(3.3.3.2)" Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply," (repair path) r - reply Status, s - sia Status"  " Protecting Node P 192.168.1.0/24, 1 successors, FD is 307200, serno 7" via 1.1.1.1 (307200/281600), Ethernet0/0" via 3.3.3.3 (332800/307200), Ethernet0/2, (LFA)" A "©2012 Cisco Systems Inc. All rights reserved. 57
  58. 58. •  It s possible to converge in under one second using any protocol, with the right network design •  IP-FRR reduces convergence time to 10’s of micro-seconds •  Rules of Thumb:   More aggregation tends towards better performance for EIGRP   Less aggregation tends towards better performance for Link State protocols   If you re going to use link state protocols, tune the timers; but if you tune the timers, be careful with HA features, like GR/NSF©2012 Cisco Systems Inc. All rights reserved. 58
  59. 59. Design and Topology Considerations©2012 Cisco Systems Inc. All rights reserved. 59
  60. 60. For Your Reference •  State Full Mesh •  Hierarchy and Aggregation •  Hub and Spoke •  DMVPN©2012 Cisco Systems Inc. All rights reserved. 60
  61. 61. •  Full mesh topologies are complex: 2 routers = 1 link 3 routers = 3 links 4 routers = 6 links 5 routers = 10 links 6 routers = 15 links … Links - 1 •  Adjacencies = Links •  2©2012 Cisco Systems Inc. All rights reserved. 61
  62. 62. •  Flooding routing information through a full mesh topology is also complicated •  Each router will, with optimal timing, receive at least one copy of every new piece of information from each neighbor on the full mesh •  There are some techniques you can use to reduce the amount of flooding in a full mesh New Information©2012 Cisco Systems Inc. All rights reserved. 62
  63. 63. •  OSPF and IS-IS can both use mesh groups to reduce the flooding in a full mesh network •  Mesh groups are manually configured designated routers on the full mesh •  Any LSPs received will not be retransmitted back out any other interface on the router in the same mesh-group •  This will reduce the number of times information is flooded over a full mesh topology •  This isn’t a commonly used configuration on each serial interface:" interface serial x" ip ospf database-filter all out" or:" isis mesh-group 1"©2012 Cisco Systems Inc. All rights reserved. 63
  64. 64. Summarize •  Routes must be advertised between every pair of peers in the mesh so each router has the correct next hop and routing information •  Treat a full mesh as a hierarchical network in Summarize Summarize disguise! •  Address your the links so they can be summarized to a single advertisement at the edge Summarize Summarize Summarize©2012 Cisco Systems Inc. All rights reserved. 64
  65. 65. Use ip ospf database-filter all out to manually designate flooding points and increase scaling through OSPF a Full Mesh Use isis mesh-group or isis mesh-group blocked to Manually Designate Flooding Points IS-IS and Increase Scaling Through a Full Mesh EIGRP Summarize into and out of the Full Mesh©2012 Cisco Systems Inc. All rights reserved. 65
  66. 66. •  OSPF has a hard edge at flooding domain borders •  Summarization and filtering can occur Summarization at this border area 0 Summarization and filtering can also be configured at routers redistributing routes into OSPF •  In a two layer hierarchy, the flooding domain border naturally lies on the aggregation/core boundary©2012 Cisco Systems Inc. All rights reserved. 66
  67. 67. •  In a three layer hierarchy, the decision of where to place the area border is more High Degree of Complexity difficult •  Examples would include full mesh areas, data centers with a large amount of parallelism, and large hub and spoke deployments •  Typically, the best best is to flow around complex areas of the network, attempting to separate them into different areas High Degree of Complexity©2012 Cisco Systems Inc. All rights reserved. 67
  68. 68. For Your Reference •  IS-IS has a hard edge at flooding domain borders, as well, but it s softer than OSPF s because the L2 routing L1 domain can (and normally does) overlap with the L1 domains •  Summarization and filtering can occur L2 at this border Summarization and filtering can also be configured at redistribution points •  In a two layer hierarchy, the flooding domain border naturally lies on the L1 aggregation/core boundary L1©2012 Cisco Systems Inc. All rights reserved. 68
  69. 69. For Your Reference •  In a three layer hierarchy, the decision of where to place the area border is High Degree of Complexity more difficult •  Typically, the best best is to flow around complex areas of the network, attempting to separate them into different areas •  Examples would include full mesh areas, data centers with a large amount of parallelism, and large hub and spoke deployments High Degree of Complexity©2012 Cisco Systems Inc. All rights reserved. 69
  70. 70. •  The depth of the hierarchy doesn’t alter the way EIGRP is deployed; there are no hard edges High Degree Core of Complexity •  Divide complexity with summarization points •  Summarize at every boundary where possible Distribution Aggregate reachability information Aggregate topology information Aggregate traffic flows •  A place to apply traffic policy Summarize Access High Degree of Complexity©2012 Cisco Systems Inc. All rights reserved. 70
  71. 71. EIGRP chooses the metric of the lowest cost 10.1.0.0/23 component route as the summary metric Metric 10 30 A 10.2.0.0/23 What happens if the summary metric changes? Metric 20 •  If the component the metric was taken from flaps, the summary flaps as well! •  You’re using the summary to hide reachability B information, but it’s passing metric information C through 10.1.0.0/24 10.1.1.0/24 10.2.0.0/24 10.2.1.0/24 Metric 30 10 Metric 20 Metric 30 Metric 20 •  Routers beyond the summary are still working to keep up with the changes©2012 Cisco Systems Inc. All rights reserved. 71
  72. 72. CSCed01736 •  Could use loopback interface to force the metric to 10.1.0.0/23 remain constant A Metric 1 •  Create a loopback interface within the summary address range with a lower metric (Use delay to force the metric value!) than any other component •  But the summary to not be withdrawn when all comments are lost, 10.1.0.0/23 as the loopback doesn’t ever go down B •  A better solution is to use the summary-metric command which established a constant metric value thereby: 10.1.0.0/24 10.1.1.0/24 Metric 10 Metric 20 •  Eliminate re-computing the summary metric when components change router eigrp CISCO
 address-family ipv4 auto 4453
 •  Allows the summary to be withdrawn network 10.0.0.0
 af-interface Ethernet0/0
 when all comments are lost summary-address 10.1.0.0/23
 exit-af-interface
 topology base
 summary-metric 10.1.0.0/23 10000 1 255 1 1500"©2012 Cisco Systems Inc. All rights reserved. 72
  73. 73. CSCed01736 •  We would like C to be able to receive as few routes as possible 10.1.0.0/16 •  We still optimally route to 10.1.1.0/24 and 10.1.2.0/24 dynamically 10.1.1.0/24 10.1.2.0/24 •  We could use a combination of static routes and route filters to advertise both 10.1.0.0/16 A B and the more specific to C •  This is complicated, and difficult to maintain 10.1.0.0/16 10.1.0.0/16 C©2012 Cisco Systems Inc. All rights reserved. 73
  74. 74. CSCed01736 •  The simplest way to handle this is to configure a leak list on the summary route 10.1.0.0/16 10.1.1.0/24 10.1.2.0/24 A B route-map LeakList permit 10
 match ip address 1
 !
 10.1.0.0/16 10.1.0.0/16 access-list 1 permit 10.1.1.0
 !
 router eigrp CISCO
 10.1.1.0/24 address-family ipv4 autonomous-system 4453
 af-interface Serial0/0
 summary-address 10.1.0.0 255.255.0.0 leak-map LeakList" C©2012 Cisco Systems Inc. All rights reserved. 74
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