Download - RS Chapter8
-
7/26/2019 RS Chapter8
1/60
-
7/26/2019 RS Chapter8
2/60
Presentation_ID 2 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Chapter 8
8.1 Characteristics of OSPF
8.2 Configuring Single-area OSPFv2
8.3 Configure Single-area OSPFv3
-
7/26/2019 RS Chapter8
3/60
Presentation_ID 3 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Chapter 8: Objectives
-
7/26/2019 RS Chapter8
4/60
Presentation_ID 4 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Open Shortest Path First
Evolution of OSPF
Interior Gateway Protocols
19881989
updated in2008
-
7/26/2019 RS Chapter8
5/60
Presentation_ID 5 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Open Shortest Path First
Features of OSPF
-
7/26/2019 RS Chapter8
6/60
Presentation_ID 6 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Open Shortest Path First
Components of OSPF
-
7/26/2019 RS Chapter8
7/60
Presentation_ID 7 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Open Shortest Path First
Components of OSPF (cont.)
OSPF Routers Exchange Packets - These packets are
used to discover neighboring routers and also toexchange routing information to maintain accurateinformation about the network.
-
7/26/2019 RS Chapter8
8/60
Presentation_ID 8 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Open Shortest Path First
Link-State Operation
If a neighbor is present,the OSPF-enabledrouter attempts toestablish a neighboradjacency with thatneighbor
-
7/26/2019 RS Chapter8
9/60
Presentation_ID 9 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Open Shortest Path First
Link-State Operation (cont.)
LSAs contain the stateand cost of each directly
connected link. Routers flood their LSAs
to adjacent neighbors. Adjacent neighbors
receiving the LSA
immediately flood the LSAto other directly connectedneighbors, until all routersin the area have all LSAs.
-
7/26/2019 RS Chapter8
10/60
Presentation_ID 10 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Open Shortest Path First
Link-State Operation
Build the topology tablebased on the received
LSAs. This database eventually
holds all the informationabout the topology of thenetwork.
Execute the SPFAlgorithm.
-
7/26/2019 RS Chapter8
11/60
Presentation_ID 11 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Open Shortest Path First
Link-State Operation (cont.)
From the SPF tree,the best paths areinserted into therouting table.
-
7/26/2019 RS Chapter8
12/60
Presentation_ID 12 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Open Shortest Path First
Single-area and Multiarea OSPF
-
7/26/2019 RS Chapter8
13/60
Presentation_ID 13 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Open Shortest Path First
Single-area and Multiarea OSPF (cont.)
-
7/26/2019 RS Chapter8
14/60
Presentation_ID 14 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Messages
Encapsulating OSPF Messages
-
7/26/2019 RS Chapter8
15/60
Presentation_ID 15 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Messages
Types of OSPF Packets
-
7/26/2019 RS Chapter8
16/60
Presentation_ID 16 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Messages
Hello Packet
OSPF Type 1 packet = Hello packet:
Discover OSPF neighbors and establishneighbor adjacencies.
Advertise parameters on which two routers
must agree to become neighbors. Elect the Designated Router (DR) andBackup Designated Router (BDR) onmultiaccess networks like Ethernet andFrame Relay.
-
7/26/2019 RS Chapter8
17/60
Presentation_ID 17 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Messages
Hello Packet (cont.)
-
7/26/2019 RS Chapter8
18/60
Presentation_ID 18 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Messages
Hello Packet Intervals
OSPF Hello packets are transmitted: To 224.0.0.5 in IPv4 and FF02::5 in IPv6 (all OSPF
routers) Every 10 seconds (default on multiaccess and point-to-
point networks)
Every 30 seconds (default on non-broadcastmultiaccess [NBMA] networks)
Dead interval is the period that the router waits toreceive a Hello packet before declaring the neighbor
down Router floods the LSDB with information about down
neighbors out all OSPF enabled interfaces Ciscos default is 4 times the Hello interval
-
7/26/2019 RS Chapter8
19/60
Presentation_ID 19 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Messages
Link-State Updates
-
7/26/2019 RS Chapter8
20/60
Presentation_ID 20 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Operation
OSPF Operational States
When an OSPF router is
initially connected to anetwork, it attempts to: Create adjacencies
with neighbors
Exchange routinginformation Calculate the best
routes Reach convergence OSPF progresses
through several stateswhile attempting toreach convergence.
-
7/26/2019 RS Chapter8
21/60
Presentation_ID 21 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Operation
Establish Neighbor Adjacencies
-
7/26/2019 RS Chapter8
22/60
-
7/26/2019 RS Chapter8
23/60
Presentation_ID 23 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Operation
OSPF DR and BDR
-
7/26/2019 RS Chapter8
24/60
Presentation_ID 24 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Operation
Synchronizing OSPF Database
-
7/26/2019 RS Chapter8
25/60
Presentation_ID 25 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Operation
Synchronizing OSPF Database (cont.)
-
7/26/2019 RS Chapter8
26/60
Presentation_ID 26 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Router ID
OSPF Network Topology
-
7/26/2019 RS Chapter8
27/60
Presentation_ID 27 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Router ID
Router IDs
-
7/26/2019 RS Chapter8
28/60
Presentation_ID 28 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Configure Single-area OSPFv2
The network Command
-
7/26/2019 RS Chapter8
29/60
Presentation_ID 29 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
By default, OSPF messages are forwarded out all OSPF-enabledinterfaces. However, these messages really only need to be sent
out interfaces connecting to other OSPF-enabled routers.
Sending out unneeded messages on a LAN affects the network inthree ways:
Inefficient Use of Bandwidth
Inefficient Use of Resources
Increased Security Risk
The Passive Interface feature helps limiting the scope of routing
updates advertisements.
Configure Single-Area OSPFv2
Passive Interface
-
7/26/2019 RS Chapter8
30/60
Presentation_ID 30 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Configure Single-area OSPFv2
Configuring Passive Interfaces
Use thepassive-interface routerconfiguration mode command to prevent thetransmission of routing messages through arouter interface, but still allow that network tobe advertised to other routers.
-
7/26/2019 RS Chapter8
31/60
Presentation_ID 31 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Cost
OSPF Metric = CostCost = reference bandwidth / interface bandwidth(default reference bandwidth is 10^8)Cost = 100,000,000 bps / interface bandwidth in bps
-
7/26/2019 RS Chapter8
32/60
Presentation_ID 32 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Cost
OSPF Accumulates Costs
Cost of an OSPF route is the accumulated value from one router to thedestination network.
-
7/26/2019 RS Chapter8
33/60
Presentation_ID 33 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Cost
Adjusting the Reference Bandwidth
Use thecommand - auto-cost reference-bandwidth Must be configured on every router in the OSPF domain
Notice that the value is expressed in Mb/s: Gigabit Ethernet -auto-cost reference-bandwidth 1000 10 Gigabit Ethernet -auto-cost reference-bandwidth 10000
-
7/26/2019 RS Chapter8
34/60
-
7/26/2019 RS Chapter8
35/60
Presentation_ID 35 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Cost
Adjusting the Interface Bandwidths
-
7/26/2019 RS Chapter8
36/60
Presentation_ID 36 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Cost
Manually Setting the OSPF Cost
Both thebandwidth interface command and theip ospf cost interfacecommand achieve the same result, which is to provide an accurate
value for use by OSPF in determining the best route.
-
7/26/2019 RS Chapter8
37/60
Presentation_ID 37 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Verify OSPF
Verify OSPF Neighbors
Verify that the router has formed an adjacency with
its neighboring routers.
-
7/26/2019 RS Chapter8
38/60
Presentation_ID 38 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Verify OSPF
Verify OSPF Protocol Settings
-
7/26/2019 RS Chapter8
39/60
Presentation_ID 39 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Verify OSPF
Verify OSPF Process Information
-
7/26/2019 RS Chapter8
40/60
Presentation_ID 40 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Verify OSPF
Verify OSPF Interface Settings
-
7/26/2019 RS Chapter8
41/60
Presentation_ID 41 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPFv2 vs. OSPFv3
OSPFv3
-
7/26/2019 RS Chapter8
42/60
Presentation_ID 42 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPFv2 vs. OSPFv3
Similarities Between OSPFv2 to OSPFv3
-
7/26/2019 RS Chapter8
43/60
Presentation_ID 43 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPFv2 vs. OSPFv3
Differences Between OSPFv2 to OSPFv3
-
7/26/2019 RS Chapter8
44/60
Presentation_ID 44 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPFv2 vs. OSPFv3
Link-Local Addresses
FF02::5 address is the all OSPF router addressFF02::6 is the DR/BDR multicast address
-
7/26/2019 RS Chapter8
45/60
Presentation_ID 45 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Configuring OSFPv3
OSPFv3 Network Topology
-
7/26/2019 RS Chapter8
46/60
Presentation_ID 46 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Configuring OSFPv3
OSPFv3 Network Topology (cont.)
-
7/26/2019 RS Chapter8
47/60
Presentation_ID 47 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Configuring OSFPv3
Link-LocalAddresses
Link-local addresses are automatically created when an IPv6 global unicast
address is assigned to the interface (required). Global unicast addresses are not required. Cisco routers create the link-local address using FE80::/10 prefix and the
EUI-64 process unless the router is configured manually, EUI-64 involves using the 48-bit Ethernet MAC address, inserting FFFE in
the middle and flipping the seventh bit. For serial interfaces, Cisco uses theMAC address of an Ethernet interface. Notice in the figure that all three interfaces are using the same link-local
address.
-
7/26/2019 RS Chapter8
48/60
Presentation_ID 48 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Configuring OSFPv3
Assigning Link-Local AddressesManuallyconfiguring the link-local addressprovides the abilityto create anaddress that isrecognizable andeasier to remember.
-
7/26/2019 RS Chapter8
49/60
Presentation_ID 49 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Configuring OSFPv3
Configuring the OSPFv3 Router ID
-
7/26/2019 RS Chapter8
50/60
Presentation_ID 50 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Configuring OSFPv3
Configuring the OSPFv3 Router ID (cont.)
-
7/26/2019 RS Chapter8
51/60
Presentation_ID 51 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Configuring OSFPv3
Modifying an OSPFv3 Router ID
-
7/26/2019 RS Chapter8
52/60
Presentation_ID 52 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
OSPF Configuring OSFPv3
Enabling OSPFv3 on Interfaces
Instead of using thenetwork router configuration modecommand to specify matching interface addresses,
OSPFv3 is configured directly on the interface.
-
7/26/2019 RS Chapter8
53/60
Presentation_ID 53 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Verify OSPFv3
Verify OSPFv3 Neighbors/Protocol Settings
-
7/26/2019 RS Chapter8
54/60
Presentation_ID 54 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Verify OSPFv3
Verify OSPFv3 Interfaces
-
7/26/2019 RS Chapter8
55/60
Presentation_ID 55 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Verify OSPFv3
Verify IPv6 Routing Table
-
7/26/2019 RS Chapter8
56/60
Presentation_ID 56 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Chapter 8: SummaryOSPF:
For IPv4 is OSPFv2
For IPv6 is OSPFv3
Classless, link-state routing protocol with a default administrativedistance of 110, and is denoted in the routing table with a routesource code of O
OSPFv2 is enabled with therouter ospf process-id globalconfiguration mode command. The process-id value is locallysignificant, which means that it does not need to match other OSPFrouters to establish adjacencies with those neighbors.
Network command uses the wildcard-mask value which is theinverse of the subnet mask, and the area-id value
-
7/26/2019 RS Chapter8
57/60
Presentation_ID 57 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Chapter 8: Summary (cont.)OSPF:
By default, OSPF Hello packets are sent every 10 seconds onmultiaccess and point-to-point segments and every 30 seconds on
NBMA segments (Frame Relay, X.25, ATM), and are used by OSPFto establish neighbor adjacencies. The Dead interval is four times theHello interval, by default.
For routers to become adjacent, their Hello interval, Dead interval,
network types, and subnet masks must match. Use theshow ip ospfneighborscommand to verify OSPF adjacencies.
In a multiaccess network, OSPF elects a DR to act as collection anddistribution point for LSAs sent and received. A BDR is elected to
assume the role of the DR should the DR fail. All other routers areknown as DROTHERs. All routers send their LSAs to the DR, whichthen floods the LSA to all other routers in the multiaccess network.
-
7/26/2019 RS Chapter8
58/60
Presentation_ID 58 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Chapter 8: Summary (cont.)OSPF:
In multiaccess networks, the router with the highest router ID is the
DR, and the router with the second highest router ID is the BDR. Thiscan be superseded by theip ospf priority command on thatinterface. The router with the highest priority value is the DR, andnext-highest the BDR.
Theshow ip protocols command is used to verify important OSPFconfiguration information, including the OSPF process ID, the routerID, and the networks the router is advertising.
OSPFv3 is enabled on an interface and not under routerconfiguration mode. OSPFv3 needs link-local addresses to be
configured. IPv6 Unicast routing must be enabled for OSPFv3. A 32-bit router-ID is required before an interface can be enabled forOSPFv3.
-
7/26/2019 RS Chapter8
59/60
Presentation_ID 59 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Chapter 8: Summary (cont.)OSPF:
Theshow ip protocols command is used to verify importantOSPFv2 configuration information, including the OSPF process ID,
the router ID, and the networks the router is advertising.
OSPFv3
Enabled on an interface and not under router configurationmode
Needs link-local addresses to be configured. IPv6
Unicast routing must be enabled for OSPFv3
32-bit router-ID is required before an interface can be enabled
for OSPFv3 show ipv6 protocols command is a quick way to verify
configuration information (OSPF process ID, the router ID, andthe interfaces enabled for OSPFv3)
-
7/26/2019 RS Chapter8
60/60
Presentation_ID 60 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential