Vlsm
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© 2002, Cisco Systems, Inc. All rights reserved.
Variable-Length Subnet Masks
©©2002, 2002,Cisco CiscoSystems, Systems,Inc. Inc.All Allrights rightsreserved. reserved.
ICND v2.0—5-2
2
What Is a Variable-Length Subnet Mask?
• Subnet 172.16.14.0/24 is divided into smaller subnets: – Subnet with one mask (/27) – Then further subnet one of the unused /27 subnets into multiple /30 subnets © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-3
Calculating VLSMs
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-4
A Working VLSM Example
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-5
What Is Route Summarization?
• Routing protocols can summarize addresses of several networks into one address © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-6
Summarizing Within an Octet
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-7
Summarizing Addresses in a VLSMDesigned Network
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-8
Implementation Considerations
• Multiple IP addresses must have the same highest-order bits. • Routing decisions are made based on the entire address. • Routing protocols must carry the prefix (subnet mask) length.
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-9
Route Summarization Operation in Cisco Routers
192.16.5.33 192.16.5.32 192.16.5.0 192.16.0.0 0.0.0.0
/32 /27 /24 /16 /0
Host Subnet Network Block of Networks Default
• Supports host-specific routes, blocks of networks, default routes • Routers use the longest match
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-10
Summarizing Routes in a Discontiguous Network
• RIPv1 and IGRP do not advertise subnets, and therefore cannot support discontiguous subnets. • OSPF, EIGRP, and RIPv2 can advertise subnets, and therefore can support discontiguous subnets. © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-11
Link-State and Balanced Hybrid Routing
©©2002, 2002,Cisco CiscoSystems, Systems,Inc. Inc.All Allrights rightsreserved. reserved.
ICND v2.0—5-12
12
Link-State Routing Protocols
• After initial flood, pass small event-triggered link-state updates to all other routers © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-13
Link-State Network Hierarchy Example
• Minimizes routing table entries • Localizes impact of a topology change within an area © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-14
Link-State Routing Protocol Algorithms
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-15
Benefits of Link-State Routing • Fast convergence: changes are reported immediately by the source affected. • Robustness against routing loops: – Routers know the topology. – Link-state packets are sequenced and acknowledged. • By careful (hierarchical) network design, you can utilize resources optimally.
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-16
Caveats of Link-State Routing • Significant demands for resources: – Memory (three tables: adjacency, topology, forwarding) – CPU (Dijkstra’s algorithm can be intensive, especially when a lot of instabilities are present.) • Requires very strict network design (when more areas— area routing) • Problems with partitioning of areas • Configuration generally simple but can be complex when tuning various parameters and when the design is complex • Troubleshooting easier than in distance vector routing © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-17
Drawbacks to Link-State Routing Protocols
• Initial discovery may cause flooding. • Memory- and processor-intensive.
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-18
Enabling OSPF
©©2002, 2002,Cisco CiscoSystems, Systems,Inc. Inc.All Allrights rightsreserved. reserved.
ICND v2.0—5-19
19
Introducing OSPF
•Open standard •Shortest path first (SPF) algorithm •Link-state routing protocol (vs. distance vector) © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-20
OSPF as a Link-State Protocol • OSPF propagates link-state advertisements rather than routing table updates. • LSAs are flooded to all OSPF routers in the area. • The OSPF link-state database is pieced together from the LSAs generated by the OSPF routers. • OSPF uses the SPF algorithm to calculate the shortest path to a destination. – Link = router interface – State = description of an interface and its relationship to neighboring routers © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-21
OSPF Hierarchical Routing
• Consists of areas and autonomous systems • Minimizes routing update traffic © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-22
Shortest Path First Algorithm
• Places each router at the root of a tree and calculates the shortest path to each destination based on the cumulative cost • Cost = 108/bandwidth (bps) © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-23
Configuring Single Area OSPF
Router(config)#router ospf process-id
• Defines OSPF as the IP routing protocol
config-router)#network address mask area area-id
• Assigns networks to a specific OSPF area
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-24
OSPF Configuration Example
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-25
Configuring Loopback Interfaces
Router ID: • Number by which the router is known to OSPF • Default: The highest IP address on an active interface at the moment of OSPF process startup • Can be overridden by a loopback interface: Highest IP address of any active loopback interface © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-26
Verifying the OSPF Configuration Router#show ip protocols
• Verifies that OSPF is configured Router#show ip route
• Displays all the routes learned by the router Router#show ip ospf interface
• Displays area-ID and adjacency information Router#show ip ospf neighbor
• Displays OSPF-neighbor information on a per-interface basis © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-27
OSPF debug commands
Router#debug ip ospf events OSPF:hello with invalid timers on interface Ethernet0 hello interval received 10 configured 10 net mask received 255.255.255.0 configured 255.255.255.0 dead interval received 40 configured 30 Router# debug ip ospf packet OSPF: rcv. v:2 t:1 l:48 rid:200.0.0.117 aid:0.0.0.0 chk:6AB2 aut:0 auk: Router#debug ip ospf packet OSPF: rcv. v:2 t:1 l:48 rid:200.0.0.116 aid:0.0.0.0 chk:0 aut:2 keyid:1 seq:0x0
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-28
Enabling EIGRP
©©2002, 2002,Cisco CiscoSystems, Systems,Inc. Inc.All Allrights rightsreserved. reserved.
ICND v2.0—5-29
29
Balanced Hybrid Routing
• Shares attributes of both distance vector and link-state routing
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-30
Introducing EIGRP
EIGRP supports: • Rapid convergence • Reduced bandwidth usage • Multiple network-layer protocols © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-31
EIGRP Terminology
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-32
Comparing EIGRP and IGRP
• • • •
© 2002, Cisco Systems, Inc. All rights reserved.
Similar metric Same load balancing Improved convergence time Reduced network overhead
ICND v2.0—5-33
Configuring EIGRP
Router(config)#router eigrp autonomous-system
• Defines EIGRP as the IP routing protocol
outer(config-router)#network network-number
• Selects participating attached networks
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-34
EIGRP Configuration Example
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-35
Verifying the EIGRP Configuration Router#show ip eigrp neighbors
• Displays the neighbors discovered by IP EIGRP Router#show ip eigrp topology
• Displays the IP EIGRP topology table Router#show ip route eigrp
• Displays current EIGRP entries in the routing table Router#show ip protocols
• Displays the parameters and current state of the active routing protocol process Router#show ip eigrp traffic
• Displays the number of IP EIGRP packets sent and received © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-36
debug ip eigrp Command
Router#debug ip eigrp IP-EIGRP: Processing incoming UPDATE packet IP-EIGRP: Ext 192.168.3.0 255.255.255.0 M 386560 - 256000 130560 SM 360960 256000 104960 IP-EIGRP: Ext 192.168.0.0 255.255.255.0 M 386560 - 256000 130560 SM 360960 256000 104960 IP-EIGRP: Ext 192.168.3.0 255.255.255.0 M 386560 - 256000 130560 SM 360960 256000 104960 IP-EIGRP: 172.69.43.0 255.255.255.0, - do advertise out Ethernet0/1 IP-EIGRP: Ext 172.69.43.0 255.255.255.0 metric 371200 - 256000 115200 IP-EIGRP: 192.135.246.0 255.255.255.0, - do advertise out Ethernet0/1 IP-EIGRP: Ext 192.135.246.0 255.255.255.0 metric 46310656 - 45714176 596480 IP-EIGRP: 172.69.40.0 255.255.255.0, - do advertise out Ethernet0/1 IP-EIGRP: Ext 172.69.40.0 255.255.255.0 metric 2272256 - 1657856 614400 IP-EIGRP: 192.135.245.0 255.255.255.0, - do advertise out Ethernet0/1 IP-EIGRP: Ext 192.135.245.0 255.255.255.0 metric 40622080 - 40000000 622080 IP-EIGRP: 192.135.244.0 255.255.255.0, - do advertise out Ethernet0/1
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-37
Summary • EIGRP is an interior gateway protocol suited for many different topologies and media. • EIGRP is an enhanced version of the IGRP developed by Cisco, with improved convergence properties and operating efficiency over IGRP. • Use the router eigrp and network commands to create an EIGRP routing process. • Use the show ip eigrp commands to display information about your EIGRP configuration. • To display information on EIGRP packets, use the debug ip eigrp privileged EXEC command. © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-38
Variable-Length Subnet Masks
©©2002, 2002,Cisco CiscoSystems, Systems,Inc. Inc.All Allrights rightsreserved. reserved.
ICND v2.0—5-2
2
What Is a Variable-Length Subnet Mask?
• Subnet 172.16.14.0/24 is divided into smaller subnets: – Subnet with one mask (/27) – Then further subnet one of the unused /27 subnets into multiple /30 subnets © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-3
Calculating VLSMs
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-4
A Working VLSM Example
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-5
What Is Route Summarization?
• Routing protocols can summarize addresses of several networks into one address © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-6
Summarizing Within an Octet
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-7
Summarizing Addresses in a VLSMDesigned Network
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-8
Implementation Considerations
• Multiple IP addresses must have the same highest-order bits. • Routing decisions are made based on the entire address. • Routing protocols must carry the prefix (subnet mask) length.
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-9
Route Summarization Operation in Cisco Routers
192.16.5.33 192.16.5.32 192.16.5.0 192.16.0.0 0.0.0.0
/32 /27 /24 /16 /0
Host Subnet Network Block of Networks Default
• Supports host-specific routes, blocks of networks, default routes • Routers use the longest match
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-10
Summarizing Routes in a Discontiguous Network
• RIPv1 and IGRP do not advertise subnets, and therefore cannot support discontiguous subnets. • OSPF, EIGRP, and RIPv2 can advertise subnets, and therefore can support discontiguous subnets. © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-11
Link-State and Balanced Hybrid Routing
©©2002, 2002,Cisco CiscoSystems, Systems,Inc. Inc.All Allrights rightsreserved. reserved.
ICND v2.0—5-12
12
Link-State Routing Protocols
• After initial flood, pass small event-triggered link-state updates to all other routers © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-13
Link-State Network Hierarchy Example
• Minimizes routing table entries • Localizes impact of a topology change within an area © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-14
Link-State Routing Protocol Algorithms
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-15
Benefits of Link-State Routing • Fast convergence: changes are reported immediately by the source affected. • Robustness against routing loops: – Routers know the topology. – Link-state packets are sequenced and acknowledged. • By careful (hierarchical) network design, you can utilize resources optimally.
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-16
Caveats of Link-State Routing • Significant demands for resources: – Memory (three tables: adjacency, topology, forwarding) – CPU (Dijkstra’s algorithm can be intensive, especially when a lot of instabilities are present.) • Requires very strict network design (when more areas— area routing) • Problems with partitioning of areas • Configuration generally simple but can be complex when tuning various parameters and when the design is complex • Troubleshooting easier than in distance vector routing © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-17
Drawbacks to Link-State Routing Protocols
• Initial discovery may cause flooding. • Memory- and processor-intensive.
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-18
Enabling OSPF
©©2002, 2002,Cisco CiscoSystems, Systems,Inc. Inc.All Allrights rightsreserved. reserved.
ICND v2.0—5-19
19
Introducing OSPF
•Open standard •Shortest path first (SPF) algorithm •Link-state routing protocol (vs. distance vector) © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-20
OSPF as a Link-State Protocol • OSPF propagates link-state advertisements rather than routing table updates. • LSAs are flooded to all OSPF routers in the area. • The OSPF link-state database is pieced together from the LSAs generated by the OSPF routers. • OSPF uses the SPF algorithm to calculate the shortest path to a destination. – Link = router interface – State = description of an interface and its relationship to neighboring routers © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-21
OSPF Hierarchical Routing
• Consists of areas and autonomous systems • Minimizes routing update traffic © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-22
Shortest Path First Algorithm
• Places each router at the root of a tree and calculates the shortest path to each destination based on the cumulative cost • Cost = 108/bandwidth (bps) © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-23
Configuring Single Area OSPF
Router(config)#router ospf process-id
• Defines OSPF as the IP routing protocol
config-router)#network address mask area area-id
• Assigns networks to a specific OSPF area
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-24
OSPF Configuration Example
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-25
Configuring Loopback Interfaces
Router ID: • Number by which the router is known to OSPF • Default: The highest IP address on an active interface at the moment of OSPF process startup • Can be overridden by a loopback interface: Highest IP address of any active loopback interface © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-26
Verifying the OSPF Configuration Router#show ip protocols
• Verifies that OSPF is configured Router#show ip route
• Displays all the routes learned by the router Router#show ip ospf interface
• Displays area-ID and adjacency information Router#show ip ospf neighbor
• Displays OSPF-neighbor information on a per-interface basis © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-27
OSPF debug commands
Router#debug ip ospf events OSPF:hello with invalid timers on interface Ethernet0 hello interval received 10 configured 10 net mask received 255.255.255.0 configured 255.255.255.0 dead interval received 40 configured 30 Router# debug ip ospf packet OSPF: rcv. v:2 t:1 l:48 rid:200.0.0.117 aid:0.0.0.0 chk:6AB2 aut:0 auk: Router#debug ip ospf packet OSPF: rcv. v:2 t:1 l:48 rid:200.0.0.116 aid:0.0.0.0 chk:0 aut:2 keyid:1 seq:0x0
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-28
Enabling EIGRP
©©2002, 2002,Cisco CiscoSystems, Systems,Inc. Inc.All Allrights rightsreserved. reserved.
ICND v2.0—5-29
29
Balanced Hybrid Routing
• Shares attributes of both distance vector and link-state routing
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-30
Introducing EIGRP
EIGRP supports: • Rapid convergence • Reduced bandwidth usage • Multiple network-layer protocols © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-31
EIGRP Terminology
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-32
Comparing EIGRP and IGRP
• • • •
© 2002, Cisco Systems, Inc. All rights reserved.
Similar metric Same load balancing Improved convergence time Reduced network overhead
ICND v2.0—5-33
Configuring EIGRP
Router(config)#router eigrp autonomous-system
• Defines EIGRP as the IP routing protocol
outer(config-router)#network network-number
• Selects participating attached networks
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-34
EIGRP Configuration Example
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-35
Verifying the EIGRP Configuration Router#show ip eigrp neighbors
• Displays the neighbors discovered by IP EIGRP Router#show ip eigrp topology
• Displays the IP EIGRP topology table Router#show ip route eigrp
• Displays current EIGRP entries in the routing table Router#show ip protocols
• Displays the parameters and current state of the active routing protocol process Router#show ip eigrp traffic
• Displays the number of IP EIGRP packets sent and received © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-36
debug ip eigrp Command
Router#debug ip eigrp IP-EIGRP: Processing incoming UPDATE packet IP-EIGRP: Ext 192.168.3.0 255.255.255.0 M 386560 - 256000 130560 SM 360960 256000 104960 IP-EIGRP: Ext 192.168.0.0 255.255.255.0 M 386560 - 256000 130560 SM 360960 256000 104960 IP-EIGRP: Ext 192.168.3.0 255.255.255.0 M 386560 - 256000 130560 SM 360960 256000 104960 IP-EIGRP: 172.69.43.0 255.255.255.0, - do advertise out Ethernet0/1 IP-EIGRP: Ext 172.69.43.0 255.255.255.0 metric 371200 - 256000 115200 IP-EIGRP: 192.135.246.0 255.255.255.0, - do advertise out Ethernet0/1 IP-EIGRP: Ext 192.135.246.0 255.255.255.0 metric 46310656 - 45714176 596480 IP-EIGRP: 172.69.40.0 255.255.255.0, - do advertise out Ethernet0/1 IP-EIGRP: Ext 172.69.40.0 255.255.255.0 metric 2272256 - 1657856 614400 IP-EIGRP: 192.135.245.0 255.255.255.0, - do advertise out Ethernet0/1 IP-EIGRP: Ext 192.135.245.0 255.255.255.0 metric 40622080 - 40000000 622080 IP-EIGRP: 192.135.244.0 255.255.255.0, - do advertise out Ethernet0/1
© 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-37
Summary • EIGRP is an interior gateway protocol suited for many different topologies and media. • EIGRP is an enhanced version of the IGRP developed by Cisco, with improved convergence properties and operating efficiency over IGRP. • Use the router eigrp and network commands to create an EIGRP routing process. • Use the show ip eigrp commands to display information about your EIGRP configuration. • To display information on EIGRP packets, use the debug ip eigrp privileged EXEC command. © 2002, Cisco Systems, Inc. All rights reserved.
ICND v2.0—5-38
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