1 Introduction to Routing Session 2 Presentation_ID.scr 1
Agenda Addressing Concepts Routing Protocols Statics and Defaults 3 ISO OSI Reference Model Routing Information Protocol (RIP and RIPv2) L7 L6 L5 L4 L3 L2 L1 Application Presentation Session Transport Network Layer Data Link Control Physical Layer Interior Gateway Routing Protocol (IGRP) Open Shortest Path First (OSPF) Protocol NetWare Link Services Protocol (NLSP) Intermediate System to Intermediate System (IS-IS) Enhanced IGRP (EIGRP) Border Gateway Protocol (BGP) 4 Presentation_ID.scr 2
Router Functions Routing = building maps and giving directions Switching = moving packets between interfaces Routers are packet switches Path determination is overhead 5 Introduction to IP Addresses UNIX Host Internet TCP/IP UNIX Host Company A Company B Unique addressing allows communication between end stations Path choice is based on location Location is represented by an address 6 Presentation_ID.scr 3
IP Addressing 32 Bits Network Host 8 Bits 8 Bits 8 Bits 8 Bits 172. 16. 122. 204 7 IP Address Classes Class A: Class B: Class C: N H H H N N H H N N N H Class D: for multicast N = Network number assigned by NIC H = Host number assigned by network administrator 8 Presentation_ID.scr 4
Host Addresses 172.16.200.11 E0 E1 10.1.1.1 172.16.3.10 10.250.8.11 172.16.12.12 10.180.30.118 IP: 172.16.2.1 IP: 10.6.24.2 Routing Table 172.16. 12. 12 Network Host Network 172.16.0.0 10.0.0.0 Interface E0 E1 9 Subnet Addressing 172.16.2.11 E0 E1 172.16.3.5 172.16.2.2 172.16.3.100 172.16.2.160 172.16.3.150 IP: 172.16.2.1 IP: 172.16.3.1 Routing Table 172.16 Network 2. Subnet. 160 Host Network 172.16.2.0 172.16.3.0 Interface E0 E1 10 Presentation_ID.scr 5
Subnet Mask Network Host IP Address Default Subnet Mask 8-bit Subnet Mask 172 16 0 0 Network Host 255 255 0 0 Network Subnet Host 255 255 255 0 Use Host Bits, Starting at the High Order Bit Position 11 Discontiguous IP Subnet Where Is 172.16.0.0? 192.168.1.4 255.255.255.252.5 A.13 172.16.50.1 255.255.255.0 172.16.40.1 255.255.255.0 B.6.9 192.168.1.12 255.255.255.252 192.168.1.8 255.255.255.252.10.14 172.16.60.1 255.255.255.0 C 12 Presentation_ID.scr 6
Variable Length Subnet Mask 172.16.1.4 255.255.255.252.5 A.13 172.16.50.1 255.255.255.0 172.16.40.1 255.255.255.0 B.6.9 172.16.1.12 255.255.255.252 172.16.1.8 255.255.255.252.10.14 Conserve IP addresses C 172.16.60.1 255.255.255.0 13 IPX Addressing 80 Bits Network Node 32 Bits 48 Bits 000C 15C0 0077.0650.2328 14 Presentation_ID.scr 7
Address Configuration Router (config-if) # ip address ip-address subnet-mask Assigns an address and subnet mask Starts IP processing on an interface ipx network network Assigns a network number Starts IPX processing on an interface Must have ipx routing configured 15 Classless Prefix Notation 131.108.0.0/16 versus 255.255.0.0 Summarizable blocks of subnets 131.108.48.0 /24 131.108.49.0 /24 131.108.50.0 /24 131.108.51.0 /24 131.108.52.0 /24 131.108.53.0 /24 131.108.54.0 /24 131.108.55.0 /24 131.108.48.0 /21 16 Presentation_ID.scr 8
IP Address Configuration Router (config) # ip netmask-format {bitcount decimal hexadecimal} Sets format of network mask as seen in show commands bitcount 172.16.31.6/24 decimal 172.16.31.6 255.255.255.0 hexadecimal 172.16.31.6 0xFFFFFF00 17 Agenda Addressing Concepts Routing Protocols Statics and Defaults 18 Presentation_ID.scr 9
Convergence Time required for router to identify and use an alternate path Dependent on timer values and algorithm Difficult to predict precisely x 19 Load Balancing T1 R2 T1 N1 N2 R1 T1 R3 T1 R4 Equal cost paths Rapid failover 20 Presentation_ID.scr 10
Load Balancing R2 768K N1 N2 R1 512K R3 T1 R4 Unequal cost paths 21 Holddown I Will Ignore Routes to X While in Holddown x Sets minimum convergence time Prevents routing loops 22 Presentation_ID.scr 11
Routing Loop: A Routing Disagreement Packets for Network X Packets do not get to the destination Temporary traffic surge until convergence 23 Split Horizon Do not send routing data back in the direction from which it came 24 Presentation_ID.scr 12
Split Horizon Frame Relay Network D 1 PVC A D PVC B S0 PVC C 25 Turn off Split Horizon D Frame Relay Network A 2 B 2 C 2 PVC D 1 PVC A A 1,3 B 2 C 2 D 2 B S0 PVC C 26 Presentation_ID.scr 13
Split Horizon Frame Relay Network S0.1 B 2 C 2 D 1 PVC A D PVC B S0.3 A 2 B 2 D 1 PVC C 27 Metrics (Cost) Numeric value used to choose among paths RIP/RIPv2 is hop count and ticks (IPX) OSPF/ISIS is interface cost (bandwidth) (E)IGRP is compound BGP can be complicated Path determination depends on metric 28 Presentation_ID.scr 14
Agenda Addressing Concepts Routing Protocols Statics and Defaults 29 Routing Table One Forwarding Table Per Protocol (IP, IPX) Network # Interface Next Hop Metric Age Source 198.113.181.0 Ethernet0 192.150.42.177 [170/304793] 02:03:50 D 198.113.178.0 192.168.96.0 Ethernet0 Ethernet0 192.150.42.177 [110/9936] 02:03:50 O 192.150.42.177 [120/3] 00:00:20 R 192.168.97.0 Ethernet0 C 30 Presentation_ID.scr 15
Building the Routing Table Hardware state Dynamic Routes are learned from a protocol Static Routes are manually defined 31 Routing Protocols A B C I Know About: Network A Network B Network C Routing Update Exchanges Network Knowledge I Know About: Network X Network Y Network Z X Y Z Routers are packet switches that forward traffic based on layer 3 logical addresses Routing protocol updates are exchanged by routers to learn about paths to other logical networks Each routing protocol offers features that can make it desirable as part of an internetwork design 32 Presentation_ID.scr 16
Routing Protocol Goals Optimal path selection Loop-free routing Fast convergence Limited design administration Minimize update traffic Handle address limitations Support hierarchical topology Incorporate rapid convergence Easy to configure Adapts to changes easily and quickly Does not create a lot of traffic Scales to a large size Compatible with existing hosts and routers Supports variable length subnet masks and discontiguous subnets Supports policy routing 33 IP RIP Routing Information Protocol Widely available Hop count metric Periodic update Easy to implement Usually free RFC 1058 Simple = limited Slow convergence No VLSM No discontiguous subnets Routing loops Count to infinity 34 Presentation_ID.scr 17
RIP Distance Vector Net A E0 R1 R2 R3 Net B Net C S0 S0 S1 S0 E0 Net D Network Interface A B C D E0 S0 S0 S0 Network Interface B C A D S0 S1 S0 S1 Network Interface C D B A S0 E0 S0 S0 Send Routing Table to Neighbors 35 Broadcast Routing Updates RIP V1 36 Presentation_ID.scr 18
RIP Metric Path A 1 Hop R2 Hops T1 T1 R1 56k R3 Path B 0 Hops 37 When to Use RIP Implementation in a few hours Good for stable links Good for small networks routed in host environment Multivendor environment Non-redundant network 38 Presentation_ID.scr 19
RIP V2 RFC 1723 Cisco IOS 11.1 support Advertises masks Variable length subnet masks Route summarization Routing updates use multicast Authenticated updates using MD5 39 Multicast Routing Updates RIP V2 40 Presentation_ID.scr 20
When to Use RIPv2 Same as RIP Subnet mask support Reduce broadcast load Validated updates Multivendor environment Non-redundant network 41 IPX RIP Widely available Hop count metric Ticks (1/18 sec) Periodic update Easy to implement Free on servers Tied to SAP protocol Simple = limited Slow convergence No default route Routing loops Count to infinity 42 Presentation_ID.scr 21
IPX RIP Ticks Ticks are used to determine server timeout Default for LAN interfaces is 1 Default for WAN interfaces is 4 IPXWAN calculates for its interfaces can be set via the ipx delay number interface sub command 43 IGRP Interior Gateway Routing Protocol Cisco developed Distance vector Compound metric Cisco IOS 9.21 Periodic update No VLSM Default timers produce slow convergence 44 Presentation_ID.scr 22
IGRP Compound Metric Administrative weight Delay Bandwidth Reliability Load R1 T1 R2 56k R3 T1 = ((K * BW + (K 2 * BW) K 5 (256-load) + K * delay)) * 1 3 (reliability + K 4 )) 45 How the IGRP Metrics Work Delay Metric- Based on D1 + D2 + D3 D1 D2 D3 Bandwidth Metric-Based on 64kbps 1.5 Mbps 64 kbps 1.5 Mbps Bandwidth dominates short paths Delay dominates long paths Configure bandwidth on all interfaces 46 Presentation_ID.scr 23
When to Use IGRP Simplicity of RIP Good for small and medium networks When metrics are important Reduced routing overhead 47 Enhanced IGRP Extremely fast convergence VLSM support Discontiguous subnets Arbitrary route summarization Supports prefix and host routing Best of DV and LS Low overhead Guaranteed loop-free Reliable, incremental update-based Multiprotocol: IP, IPX, AppleTalk Easy to configure 48 Presentation_ID.scr 24
Advanced Distance Vector A B C Q 1 13 20 A B C 5 3 3 X s Table Z Y X A B C 27 12 35 A Q 2 B Z 13 C X 13 Y s Table On Startup Routing Tables Are Exchanged; Routing Table Built Based on Best Paths from Topology Table Construct neighbor tables Construct topology tables Compute routes A 27 Z 1 Q 5 X Ḅ... 12.. Ẓ... Topology Table 49 EIGRP Tables Topology table Acted upon by DUAL All routes advertised by neighbors List of neighbors for each route Routes passive or active Neighbor table Keeps adjacent neighbor s address Keeps the hold time Information for reliable transport 50 Presentation_ID.scr 25
Diffusing Update Algorithm (DUAL) DUAL is a loop-free routing algorithm that performs a diffused computation of a routing table Uses a new routing algorithm Achieves fast convergence Network changes propagate only to affected nodes ( bounded updates ) No need for route holddown Researched and developed by SRI International 51 IPX EIGRP Automatic redistribution of routes into RIP/SAP Maximum network size is 224 hops vs 15 for RIP Incremental SAPs sent, reducing bandwidth usage All other benefits of EIGRP 52 Presentation_ID.scr 26
When to Use EIGRP Very large, complex networks VLSM For fast convergence Little network design Multiprotocol support 53 Link State Routing Q s Link State Z Z s Link State Topology Information Is Kept in a Database Separate from the Routing Table Q Y A B C Q Z X 2 13 13 X s Link State X OSPF IS-IS NLSP DECnet V 54 Presentation_ID.scr 27
Link State Routing Neighbor discovery Constructing an LSA (Link State Advertisement) Distribute LSA Compute routes using SPF (Shortest Path First) On network failure New LSAs flooded All routers recompute routing tables 55 OSPF Open Shortest Path First Link state or SPF technology Developed by OSPF working group of IETF (RFC 1253) Designed expressly for TCP/IP Internet environment Fast convergence Variable-length subnet masks Discontiguous subnets No periodic updates Route authentication Delivered two years after IGRP 56 Presentation_ID.scr 28
OSPF Areas and Rules Backbone area (0) must be present All other areas must have connection to backbone Backbone must be contiguous Do not partition area (0) Backbone Router Internet Area 2 Area 3 Area 4 Area Border Router Area 0 Area 1 Autonomous System (AS) Border Router Internal Router 57 When to Use OSPF Large hierarchical networks Complex networks, except Topology restrictive Additional network design VLSM Fast convergence Multivendor 58 Presentation_ID.scr 29
IS-IS IS = Intermediate System Dual IS-IS Integrated IS-IS Metric is 6 bits wide (1-63)* All interfaces default to 10 ISO 10589 Two types of areas: Level-1 other areas Level-2 backbone Default for each level Much like OSPF 59 NetWare Link Services Protocol Derived from ISIS NLSP specs 3 levels of routers Only 2 levels are defined Spec is Novell NLSP version 1.1 http://developer.novell.com /devres/langrp/specs/nlspspec.exe http://www.novell.com/documentation /en/kayak/nw411com/ipxrtenu/docmodul/ch3.html 60 Presentation_ID.scr 30
BGP RFC 1771 Border Gateway Protocol Version 4 is current Exterior routing protocol (vs. interior) Uses TCP for transport Many options for policy enforcement Classless Inter Domain Routing (CIDR) Widely used for Internet backbone Autonomous systems 61 BGP Basics A Peering AS 100 AS 101 C B D Runs over TCP Path vector protocol Incremental update E AS 102 62 Presentation_ID.scr 31
Internal BGP (IBGP) Peering A AS 100 B D E BGP peer within the same AS Not required to be directly connected IBGP neighbors should be fully meshed Few BGP speakers in corporate network 63 External BGP (EBGP) Peering A AS 100 AS 101 C B Between BGP speakers in different AS Should be directly connected Don t run an IGP between EBGP peers 64 Presentation_ID.scr 32
Policy Drives BGP Requirements BGP AS 200 Static Route AS 100 BGP AS 400 BGP AS 300 Policy for AS 100: Always use AS 300 path to reach AS 400 65 When Not to Use BGP A Static B C ISP Runs BGP Network Number Advertise Default Network Via IGP Use a Static Route to Provide Connectivity Avoid BGP configuration by using default networks and static routes Appropriate when the local policy is the same as the ISP policy 66 Presentation_ID.scr 33
Agenda Addressing Concepts Routing Protocols Statics and Defaults 67 Static Routes Routes configured manually Useful when few or just one route exist Can be administrative burden Frequently used for default route 68 Presentation_ID.scr 34
Floating Static Routes A static route with a high distance Can be overridden by dynamic info 172.16.3.2 3 ISDN T1 172.16.3.1 3 172.16.1.0 C15C0 ip route 172.16.1.0 255.255.255.0 172.16.3.1 140 ipx route C15C0 3.0000.0c15.3628 floating-static 69 Default Routes Route used if no match is found in routing table Can be carried by routing protocols Two models Special network number: 0.0.0.0 (IP) -2 (IPX) Flagged in routing protocol Protocols support multiple models 70 Presentation_ID.scr 35
Creating a Default Route RIP, RIPv2: network 0.0.0.0 IGRP, EIGRP: ip default-network OSPF: default originate IPX: ipx route default default gateway is for host mode 71 Default IP Subnet 172.16.0.0 s0 s1 Internet Two defaults 172.16.1.0 For unknown networks For unknown subnets Controlled by ip classless 72 Presentation_ID.scr 36
Comparison of Routing Protocols Link State Traditional Distance Vector Advanced Distance Vector Scalability Good Low Excellent Bandwidth Low High Low Memory High Low Moderate CPU High Low Low Convergence Fast Slow Fast Configuration Moderate Easy Easy 73 Internet Routing Protocols IP routing protocols are characterized as Name Type Proprietary Function Updates Metric VLSM Summ RIP DV No Interior 30 Sec Hops No Auto RIPv2 DV No Interior 30 Sec Hops Yes Auto IGRP DV Yes Interior 90 Sec Comp No Auto EIGRP Adv DV Yes Interior Trig Comp Yes Both OSPF LS No Interior Trig Cost Yes Man IS-IS LS No Int/Ext Trig Cost Yes Auto BGP DV No Exterior Trig N/A N/A Man 74 Presentation_ID.scr 37
Topology/Technology Considerations Routing and services overhead is usually not a big deal when you have a lot of bandwidth (i.e. LANs) Protect WAN bandwidth using update-based protocols more bandwidth and buffers for application traffic High densities of sub(interfaces) can cause hot spots and router CPU overload NBMA (Non-Broadcast Multi-Access) technologies always require good design practices 75 For Further Reference Computer Networks, Third Edition by Andrew Tanenbaum (ISBN: 0-13349-945-6) Interconnections : Bridges and Routers by Radia Perlman (ISBN: 0-20156-332-0) Internetworking with TCP / IP, Volume 1: Principles, Protocols, and Architecture by Douglas Comer (ISBN: 0-13216-987-8) IP Routing Fundamentals by Mark Sportack (ISBN: 1-57870-071-x) IP Routing Primer by Robert Wright (ISBN: 1-57870-108-2) OSPF Network Design Solutions by Thomas, Thomas M. (ISBN: 1-57870-046-9) 76 Presentation_ID.scr 38
Thank You! Please fill out the survey This was # Introduction to Routing Related sessions: 304 Intro to IP Switching 307 Deploying IGRP/EIGRP 308 Deploying OSPF/NLSP/IS-IS 309 Deploying BGP 77 Introduction to Routing Session 78 Presentation_ID.scr 39
79 Presentation_ID.scr 40