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Introduction to Routing Session 301
301 0947_05F9_c2
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301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
Introduction to Routing Session 301
301 0947_05F9_c2
© 1999, Cisco Systems, Inc.
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Agenda
• Addressing • Concepts • Routing Protocols • Statics and Defaults
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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)
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Router Functions • Routing = building maps and giving directions • Switching = moving packets between interfaces • Routers are packet switches • Path determination is overhead 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
Introduction to IP Addresses UNIX Host
Internet TCP/IP
Company A
UNIX Host
Company B
• Unique addressing allows communication between end stations • Path choice is based on location • Location is represented by an address 301 0947_05F9_c2
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3
IP Addressing 32 Bits
Network 8 Bits
172 301 0947_05F9_c2
Host 8 Bits
.
16
8 Bits
8 Bits
. 122 . 204 7
© 1999, Cisco Systems, Inc.
IP Address Classes
• Class A:
N
H
H
H
• Class B:
N
N
H
H
• Class C:
N
N
N
H
• Class D: for multicast N = Network number assigned by NIC H = Host number assigned by network administrator 301 0947_05F9_c2
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Host Addresses
172.16.200.11
E0
10.1.1.1
E1
172.16.3.10
10.250.8.11
172.16.12.12
10.180.30.118
IP: 172.16.2.1
172 .16
Routing Table Network Interface 172.16.0.0 E0
. 12 . 12
Network 301 0947_05F9_c2
IP: 10.6.24.2
Host
10.0.0.0
E1 9
© 1999, Cisco Systems, Inc.
Subnet Addressing
172.16.2.11
E0
E1
172.16.2.2
172.16.3.100
172.16.2.160
172.16.3.150
IP: 172.16.2.1
172 .16 Network 301 0947_05F9_c2
172.16.3.5
2 .
Subnet
IP: 172.16.3.1
160 .
Host
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Routing Table Network Interface 172.16.2.0 E0 172.16.3.0
E1 10
5
Subnet Mask Network IP Address
172
Host
16
0
0
Network Default Subnet Mask
255
Host
255 Network
8-bit Subnet Mask
255
255
0
0
Subnet
Host
255
0
Use Host Bits, Starting at the High Order Bit Position 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
Discontiguous IP Subnet A Where Is 172.16.0.0?
.5
192.168.1.4 255.255.255.252
B 172.16 172.16.40.1 255.255.255.0
172 172.16.50.1 255.255.255.0 .13
.6 192.168.1.12 255.255.255.252
.9 192.168.1.8 255.255.255.252
.14 .10
172.16 172.16.60.1 255.255.255.0
C
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Variable Length Subnet Mask A .5
172.16.1.4 255.255.255.252
B
172.16.50.1 255.255.255.0 .13
.6
172.16.40.1 255.255.255.0
172.16.1.12 255.255.255.252
.9 172.16.1.8 255.255.255.252
.14 .10
172.16.60.1 255.255.255.0
C
• Conserve IP addresses 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
IPX Addressing 80 Bits
Network
Node
32 Bits
48 Bits
000C 15C0 301 0947_05F9_c2
0077.0650.2328
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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 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
Classless Prefix Notation • 131.108.0.0/16 versus 255.255.0.0 • Summarizable blocks of subnets 131.108.48.0 /24
131.108.48.0 /21
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 /24 301 0947_05F9_c2
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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
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© 1999, Cisco Systems, Inc.
Agenda
• Addressing • Concepts • Routing Protocols • Statics and Defaults
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Convergence • Time required for router to identify and use an alternate path • Dependent on timer values and algorithm • Difficult to predict precisely
x
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© 1999, Cisco Systems, Inc.
Load Balancing
T1
R2
T1
N1
N2 R4
R1 T1
R3
T1
• Equal cost paths • Rapid failover 301 0947_05F9_c2
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Load Balancing
R2
768K
N1
N2 R1
512K R3
R4 T1
• Unequal cost paths 301 0947_05F9_c2
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Holddown I Will Ignore Routes to X While in Holddown
x
• Sets minimum convergence time • Prevents routing loops 301 0947_05F9_c2
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Routing Loop: A Routing Disagreement
Packets for Network X
• Packets do not get to the destination • Temporary traffic surge until convergence 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
Split Horizon
“ Do not send routing data back in the direction from which it came
” 301 0947_05F9_c2
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Split Horizon Frame Relay Network A PVC D
1
PVC
D
B S0
PVC C
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Turn off Split Horizon A 1,3
Frame Relay Network A
2
B
2
C
2
D
1
B
2
C
2
D
2
A PVC PVC
D
B
S0
PVC C
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Split Horizon Frame Relay Network
S0.1
B
2
C
2
D
1
A PVC PVC
D S0.3
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A
2
B
2
D
1
B
PVC C
27
© 1999, Cisco Systems, Inc.
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 301 0947_05F9_c2
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14
Agenda
• Addressing • Concepts • Routing Protocols • Statics and Defaults
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© 1999, Cisco Systems, Inc.
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 Ethernet0 192.150.42.177 192.168.96.0
Ethernet0 192.150.42.177
192.168.97.0
Ethernet0
301 0947_05F9_c2
[110/9936]
02:03:50
O
[120/3]
00:00:20
R
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15
Building the Routing Table
• Hardware state • Dynamic Routes are learned from a protocol
• Static Routes are manually defined 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
Routing Protocols
A
I Know About: Network A Network B Network C
Routing Update
I Know About: Network X Network Y Network Z
B
X Y
Exchanges Network Knowledge
C
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 301 0947_05F9_c2
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Routing Protocol Goals • Optimal path selection
• Easy to configure
• Loop-free routing
• Adapts to changes easily and quickly
• Fast convergence
• Does not create a lot of traffic
• Limited design administration
• Scales to a large size
• Minimize update traffic • Handle address limitations • Support hierarchical topology
• Supports variable length subnet masks and discontiguous subnets
• Incorporate rapid convergence 301 0947_05F9_c2
• Compatible with existing hosts and routers
• Supports policy routing 33
© 1999, Cisco Systems, Inc.
IP RIP • Routing Information Protocol • Widely available • Hop count metric • Periodic update • Easy to implement • Usually free 301 0947_05F9_c2
• RFC 1058 • Simple = limited • Slow convergence • No VLSM • No discontiguous subnets • Routing loops • Count to infinity
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RIP—Distance Vector Net A
Net D
R1
R2 Net B S0 S0
E0
Network Interface A E0 B S0 C S0 D S0
R3 Net C S1
Network Interface B S0 C S1 A S0 D S1
S0
E0
Network Interface C S0 D E0 B S0 A S0
Send Routing Table to Neighbors 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
Broadcast Routing Updates
RIP V1
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RIP Metric 1 Hop Path A
Hops
R2
T1
T1 56k
R1
R3
Path B 0 Hops 301 0947_05F9_c2
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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 301 0947_05F9_c2
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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 301 0947_05F9_c2
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Multicast Routing Updates
RIP V2
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When to Use RIPv2 • Same as RIP • Subnet mask support • Reduce broadcast load • Validated updates • Multivendor environment • Non-redundant network 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
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
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IPX RIP—Ticks • Ticks are used to determine server timeout
• IPXWAN calculates for its interfaces
• Default for LAN interfaces is 1
• can be set via the ipx delay number interface sub command
• Default for WAN interfaces is 4 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
IGRP • Interior Gateway • Routing Protocol • • Cisco developed • • Distance vector • • Compound metric 301 0947_05F9_c2
Cisco IOS 9.21 Periodic update No VLSM Default timers produce slow convergence
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IGRP Compound Metric • Administrative weight
T1 R2
• Delay • Bandwidth
T1
• Reliability
56k
• Load
R1
R3
(K2 * BW) K = ((K1 * BW + (256-load) + K3* delay)) * (reliability5 + K )) 4 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
How the IGRP Metrics Work Delay MetricBased 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 301 0947_05F9_c2
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When to Use IGRP
• Simplicity of RIP • Good for small and medium networks • When metrics are important • Reduced routing overhead
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Enhanced IGRP • Extremely fast convergence • VLSM support • Discontiguous subnets • Arbitrary route summarization • Supports prefix and host routing 301 0947_05F9_c2
• Best of DV and LS • Low overhead • Guaranteed loop-free • Reliable, incremental update-based • Multiprotocol: IP, IPX®, AppleTalk • Easy to configure
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Advanced Distance Vector
A B C
1 13 20
Z
Q
Y
A B C
On Startup Routing Tables Are Exchanged; Routing Table Built Based on Best Paths from Topology Table
27 12 35
A B C
Q Z X
2 13 13
Y’s Table A B C
5 3 3
X
X’s Table
301 0947_05F9_c2
A
B ..
27 1 5 12 ..
Z Q X Z ..
Topology Table
• Construct neighbor tables • Construct topology tables • Compute routes 49
© 1999, Cisco Systems, Inc.
EIGRP Tables • Topology table
• Neighbor table
• Acted upon by DUAL • Keeps adjacent neighbor’s address • All routes advertised by neighbors • Keeps the hold time • List of neighbors for • Information for each route reliable transport • Routes passive or active 301 0947_05F9_c2
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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 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
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 301 0947_05F9_c2
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When to Use EIGRP
• Very large, complex networks • VLSM • For fast convergence • Little network design • Multiprotocol support 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
Link State Routing Z’s Link State Q’s Link State Topology Information Is Kept in a Database Separate from the Routing Table
Z
Q
Y
A B C
Q Z X
2 13 13
• OSPF X’s Link State
X
• IS-IS • NLSP • DECnet V
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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 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
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 301 0947_05F9_c2
• Fast convergence • Variable-length subnet masks • Discontiguous subnets • No periodic updates • Route authentication • Delivered two years after IGRP
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OSPF Areas and Rules Area Border Router
• Backbone area (0) must be present • All other areas must have connection to backbone
Area 2
Area 3 Area 0
Backbone Router
• Backbone must be contiguous
Area 4 Area 1
• Do not partition area (0) Internet 301 0947_05F9_c2
Internal Router
Autonomous System (AS) Border Router 57
© 1999, Cisco Systems, Inc.
When to Use OSPF • Large hierarchical networks • Complex networks, except… Topology restrictive Additional network design
• VLSM • Fast convergence • Multivendor 301 0947_05F9_c2
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IS-IS • IS = Intermediate System
• ISO 10589 • Two types of areas:
• Dual IS-IS
Level-1 other areas
• Integrated IS-IS
Level-2 backbone
• Metric is 6 bits wide (1-63)*
• Default for each level
• All interfaces default to 10
• Much like OSPF
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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 301 0947_05F9_c2
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BGP • RFC 1771
• Many options for policy enforcement
• Border Gateway Protocol
• Classless Inter Domain Routing • Version 4 is current (CIDR) • Exterior routing • Widely used for protocol (vs. Internet backbone interior) • Autonomous • Uses TCP for systems transport 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
BGP Basics Peering A
C
AS 100
AS 101 B
D
E
• Runs over TCP
AS 102
• Path vector protocol • Incremental update 301 0947_05F9_c2
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Internal BGP (IBGP) Peering AS 100 D A B
E
• • • • 301 0947_05F9_c2
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
© 1999, Cisco Systems, Inc.
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 301 0947_05F9_c2
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Policy Drives BGP Requirements Static Route
AS 200 BGP AS 100
BGP BGP
AS 400
AS 300
• Policy for AS 100: Always use AS 300 path to reach AS 400 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
When Not to Use BGP Network Number
Static A
BB
C ISP Runs BGP
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 301 0947_05F9_c2
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Agenda
• Addressing • Concepts • Routing Protocols • Statics and Defaults
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© 1999, Cisco Systems, Inc.
Static Routes
• Routes configured manually • Useful when few or just one route exist • Can be administrative burden • Frequently used for default route 301 0947_05F9_c2
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Floating Static Routes • A static route with a high distance • Can be overridden by dynamic info T1 172.16.3.2 3
ISDN
172.16.1.0 C15C0
172.16.3.1 3 ip route 172.16.1.0 255.255.255.0 172.16.3.1 140 ipx route C15C0 3.0000.0c15.3628 floating-static 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
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 301 0947_05F9_c2
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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” 301 0947_05F9_c2
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© 1999, Cisco Systems, Inc.
Default IP Subnet 172.16.0.0
Internet s0
s1
172.16.1.0
• Two defaults For unknown networks For unknown subnets
• Controlled by ip classless 301 0947_05F9_c2
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Comparison of Routing Protocols
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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
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© 1999, Cisco Systems, Inc.
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
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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 301 0947_05F9_c2
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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) 301 0947_05F9_c2
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Thank You! • Please fill out the survey • This was #301 Introduction to Routing • Related sessions: 304 Intro to IP Switching 307 Deploying IGRP/EIGRP 308 Deploying OSPF/NLSP/IS-IS 309 Deploying BGP 301 0947_05F9_c2
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