73 IP Routing Two types: direct and indirect. Routing provides for efficient network topologies....
Transcript of 73 IP Routing Two types: direct and indirect. Routing provides for efficient network topologies....
11
IP RoutingIP Routing
Two types: direct and indirect.
Routing provides for efficient network topologies.
Flat networks cannot scale.
Protocols used today are the same ones that were used back in the shared network environment.
Two types of protocols IGP and EGP. IGP provides for routing within a single AS EGP provides for routing between ASs
22
Direct RoutingDirect Routing
Network numbers must match for direct routing.
Different network numbers for indirect routing.
Remote nodes may use a combination of both direct and indirect routing.
Direct RoutingDirect Routing
Indirect RoutingIndirect RoutingStation D 140.2.1.1Station D 140.2.1.1
DirectDirectRoutingRouting Station AStation A
140.1.1.1140.1.1.1Station BStation B140.1.2.1140.1.2.1
Station CStation C140.1.3.1140.1.3.1
33
Indirect RoutingIndirect Routing
Occurs when the source and destination network or subnet do not match.
Source will ARP for a router and send the datagram to the router.
The router will either forward the packet directly to the destination or it will forward it to another router in the path to the destination.
Routers decrement the TTL field.
Routers forward the packet based on the IP address and not the MAC address.
44
A FlowchartA Flowchart
Header and checksum valid?
Decrement TTL;TTL >= 0?
If route is available, search for MACaddress in ARP
cache
Build new packet withMAC address and
route packet throughport found in routing
table.
Received ARP reply,insert MAC and IP
address intoARP table
NO
YES YES
YES
NO
NO
Packet ReceivedPacket Received
Route found?
Default route available?
Discard originalpacket
Send ICMPerror messageto originator
YES
NOMAC address
found?
Route Table lookup based on
destination address
Send ARP requestand wait for a
response
Received ARP
Reply?
YES
NO
NO
YES
55
Routing Protocols - Distance VectorRouting Protocols - Distance Vector134.4.0.0134.4.0.0
134.3.0.0134.3.0.0
1122
Network Metric Port Age134.4.0.0 1 1 xxx134.3.0.0 1 1 xxx134.5.0.0 2 2 xxx
134.5.0.0134.5.0.0
66
Updating Other Routers (Distance Updating Other Routers (Distance Vectors)Vectors) Upon initialization, each router reads its preconfigured IP address and metric (cost
in hops) of all its active ports.
Each router transmits a portion of its routing table (network ID, metric) to each “neighbor” router.
Each router uses the most recent updates from each neighbor.
Each router uses the update information to calculate its own “shortest path” (distance in hops) to a network.
Tables are updated only:
If the received information indicates a shorter path to the destination network.
If the received update information indicates a network is no longer reachable.
If a new network is found.
77
A Bigger UpdateA Bigger Update
Route HopRoute Hop
Router A
Router B
X 1Y 1Z 2
Z Y X
W
W 1X 1Y 2Z 3
Router CNetwork Hop Router PortNetwork Hop Router Port
WW 11 LocalLocal 22
XX 11 LocalLocal 11
YY 22 BB 11
ZZ 33 BB 11
Z 1Z 1Y 1Y 1Z 1Z 1Y 1Y 1
Route HopRoute HopRoute Hop
88
IP Routing TablesIP Routing Tables
Network NumberNetwork Number Next HopNext Hop HopsHops Learned fromLearned from PortPort
132.2.0.0132.2.0.0 DirectDirect 1 1 RIP RIP 11
133.3.0.0133.3.0.0 DirectDirect 1 1 RIP RIP 22
130.1.0.0130.1.0.0 DirectDirect 1 1 RIP RIP 33
134.4.0.0134.4.0.0 DirectDirect 1 1 RIP RIP 22
132.2.0.0132.2.0.0
130.1.0.0130.1.0.0
133.3.0.0133.3.0.0 134.4.0.0134.4.0.0
2.22.2 3.33.3
3.43.44.54.5
1.11.1
Port IP addressPort IP address(i.e., 132.2.2.2)(i.e., 132.2.2.2)
Routing TableRouting Table
99
UDP HeaderUDP Header UDP DataUDP Data
The Routing Information Protocol The Routing Information Protocol (Version 1)(Version 1)
DADA SASA TFTF CRCCRCDataData
IP HeaderIP Header IP DataIP Data
RIP HeaderRIP Header RIP DataRIP Data
1010
RIP Operational TypesRIP Operational Types
RIP can operate in either ACTIVE or PASSIVE mode.
Active means that it builds routing tables and responds to RIP requests.
Passive means that it can build a routing table for its own use, but it does not respond to any RIP requests.
Most workstations (PCs) use a default gateway (i.e., router) and not a routing update protocol like RIP.
1111
RIP Field DescriptionsRIP Field Descriptions
0 31
Up to 25 entriesUp to 25 entries
DADA SASA TFTF CRCCRCUDP DataUDP Data
CommandCommand VersionVersion ReservedReserved
ReservedReservedFamily of Net 1Family of Net 1
Net 1 addressNet 1 address
Set to 0Set to 0
Set to 0Set to 0
Distance of network 1Distance of network 1
Family of Net 2Family of Net 2 ReservedReserved
Net 2 addressNet 2 address
Distance of network 2Distance of network 2
Set to 0Set to 0
Set to 0Set to 0
IP HdrIP Hdr UDP HdrUDP Hdr
1212
Default Router and GatewaysDefault Router and Gateways
129.1.1.1129.1.1.1
Default RouteDefault Route129.1.1.1129.1.1.1
130.1.1.1130.1.1.1 Default RouteDefault Route130.1.1.1130.1.1.1
Default RouteDefault Route0.0.0.00.0.0.0
129.1.1.2129.1.1.2
129.1.1.2129.1.1.2
1313
Disadvantages of the RIPv1 ProtocolDisadvantages of the RIPv1 Protocol
RIPv1 only understands the shortest route to a destination, based on a simple count of router hops.
It depends on other routers for computed routing updates.
Routing tables can get large and these are broadcasted every 30 seconds.
Distances are based on hops, not real costs (such as the speed of a link).
Patched with split horizon, poison reverse, hold-down timers, triggered updates. It continues to be a router-to-router configuration. One router is fully
dependent on the next router to implement the same options.
Fix one problem and others appear.
1414
Scaling with RIPScaling with RIP
Router A
Router B
Z Y X
W
Router C
Z 1Z 1Y 1Y 1Z 1Z 1Y 1Y 1
WW 22XX 11YY 11ZZ 11
WW 22XX 11YY 11ZZ 22
WW 11XX 11YY 22ZZ 33
WW 11XX 11YY 22ZZ 33
Router A previously sent its table
1515
Routers and Subnet MasksRouters and Subnet Masks
150.1.1.0150.1.1.0255.255.255.0255.255.255.0
160.1.1.0160.1.1.0255.255.255.0255.255.255.0
150.1.3.0150.1.3.0255.255.255.0255.255.255.0
150.1.0.0150.1.0.0
160.1.0.0160.1.0.0 150.1.3.0150.1.3.0
1616
RIP FixesRIP Fixes
Split Horizon—Rule states that a router will not rebroadcast a learned route back over the interface from which the route was learned.
Hold-Down Timer—Rule states that when a router receives information about a network that is unreachable, the router must ignore all subsequent information about that network for a configurable amount of time.
Poisoned Reverse and triggered updates—Rule states a router is allowed to rebroadcast a learned route over the interface from which it learned it, but the metric is set to 16. A triggered update allows a router to broadcast its table when a network is found to be down.
1717
Split Horizon DemonstratedSplit Horizon Demonstrated
Router A
Router B
Z Y X
W
Router C
XX 11YY 11ZZ 22WW 22
XX 11YY 11WW 22
WW 11XX 11
WW 11XX 11YY 22ZZ 33
ZZ 11YY 11
1818
RIP Version 2RIP Version 2
CommandCommand VersionVersion UnusedUnusedRoute TagRoute TagAddress Family IdentifierAddress Family Identifier
Net 1 addressNet 1 addressSubnet maskSubnet mask
Next-Hop IP AddressNext-Hop IP Address
MetricMetricAddress Family IdentifierAddress Family Identifier Route TagRoute Tag
Net 2 addressNet 2 address
MetricMetricNext HopNext Hop
Subnet maskSubnet mask
DADA SASA TFTF CRCCRCUDP DataUDP DataIP HdrIP Hdr UDP HdrUDP Hdr
1919
AuthenticationAuthentication
Command Version UnusedAuthentification TypeOxFFFF
PasswordPassword
Address Family Identifier Route TagNet 2 address
Next HopSubnet mask
PasswordPasswordPasswordPasswordPasswordPassword
Metric
00 3131
2020
Subnet Mask FieldSubnet Mask Field
Command Version UnusedAuthentification TypeOxFFFF
PasswordPassword
Address Family Identifier Route TagNet 2 address
Next HopSubnet mask
PasswordPasswordPasswordPasswordPasswordPassword
Metric
00 3131
2121
Route Tag and Next-Hop FieldsRoute Tag and Next-Hop Fields
Command Version UnusedAuthentification TypeOxFFFF
PasswordPassword
Address Family Identifier Route TagNet 2 address
Next HopSubnet mask
PasswordPasswordPasswordPasswordPasswordPassword
Metric
00 3131
2222
Multicast Support Multicast Support
RIPv2 uses the multicast address of 224.0.0.9 to multicast, does not broadcast its table.
MAC address of 01-00-5E-00-00-09. Details of this conversion are covered in RFC 1700 and the
multicast section of this book
RIPv1 uses a broadcast address in both the IP header and the MAC header.
IGMP is not used for this multicast support.
2323
RIPv2 Compatibility with RIPv1RIPv2 Compatibility with RIPv1
Configuration parameters on the router for: RIPv1 only – version 1 messages will be sent RIPv1 compatibility – RIP 2 messages as broadcast RIPv2 – Messages are multicast None – No RIP messages are sent
2424
Open Shortest Path First (OSPF, RFC Open Shortest Path First (OSPF, RFC 2178)2178) Shortest-path routes based on true metrics, not just a hop count.
Computes the routes only when triggered to or every 30 minutes (whichever is less).
Pairs a network address entry with a subnet mask.
Allows for routing across equal paths.
Supports ToS.
Permits the injection of external routes (other ASs).
Authenticates route exchanges.
Quick convergence.
Direct support for multicast in both the IP header and the MAC header.
2525
An OSPF NetworkAn OSPF Network
RouterRouter
RouterRouter
RouterRouter
PCPC PCPC
PCPC
PCPC
HostHost
RouterRouter
Other AutonomousOther AutonomousSystemsSystems Backbone Area 0.0.0.0Backbone Area 0.0.0.0
Area 1Area 1 Area 2Area 2
Area 5Area 5
Area 4Area 4
2626
A Routing Protocol ComparisonA Routing Protocol Comparison
Function/Feature RIPv1 RIPv2 OSPFStandard Number RFC 1058 RFC 1723 RFC 2178Link State Protocol No No YesLarge Range ofMetrics
Hop Count(16=Infinity)
Hop Count (16 =Infinity)
Yes, based on 1- 65535
Update Policy Route Table every 30sec
Route Table every 30sec
Link state changes orevery 30 minutes
Update address Broadcast Broadcast, Multicast MulticastDead Interval 300 secs total 300 seconds total Up to 300 seconds
total. Usually shorterSupportsauthentication
No Yes Yes
Convergence Time Variable based on(number of routers xdead interval)
Variable based on(number of routers xdead interval)
Media Delay + Dead Interval
Variable LengthSubnets
No Yes Yes
SupportsSupernetting
No Yes Yes
Type of Service (TOS) No No YesMultipath routing No No YesNetwork Diameter 15 hops 15 hops N/A but up to 65535Easy to use Yes Yes No
2727
OSPF OverviewOSPF Overview
Upon initialization, each router records information about all its interfaces. Each router builds a packet known as the Link State Advertisement (LSA).
Contains a listing of all recently seen routers and their cost LSAs are restricted to being forwarded only in the orginated area
Received LSAs are flooded to all other routers. Each router makes a copy of the most recently “seen” LSA
Each router has complete knowledge of the topology of the area to which it belongs.
Adjacencies are formed between a Designated Router (and Backup DR) and other routers on a network.
Shortest Path Trees are constructed after routers exchange their databases. Router algorithm only when changes occur (or every 30 minutes, whichever is
shorter).
2828
OSPF Media SupportOSPF Media Support
Broadcast - Networks such as Ethernet, Token Ring, and FDDI.
Non-broadcast Multiaccess (NBMA) - access that does not support broadcast but allows for multiple station access such as ATM, Frame Relay, and X.25.
Point-to-Point - Links that only have two network attachments, such as two routers connected by a serial line.
2929
Router TypesRouter Types
RouterRouter RouterRouter
PCPC PCPCPCPC
HostHost
Other AutonomousOther AutonomousSystemsSystems
Backbone Area 0.0.0.0Backbone Area 0.0.0.0Internal RouterInternal Router
Area 1Area 1 Area 2Area 2 Area 4Area 4
Autonomous SystemAutonomous SystemBorder RouterBorder Router
BackboneBackboneRouterRouter
DesignatedDesignatedRouterRouter
Internal RouterInternal Router
BackupBackupDRDR
Area 3Area 3
Area BorderArea BorderRouterRouter
3030
Router Names and Routing MethodsRouter Names and Routing Methods
Three types of routing in an OSPF network: Intra-Area routing - Routing within a single area Inter-Area routing - Routing within two areas of the same AS Inter-AS routing Routing between AS systems
3131
Message TypesMessage Types
OSPF routers communicate by sending Link State Advertisement (LSAs) to each other. Type 1 - Router Links Advertisement Type 2 - Network Links Advertisement Type 3 - Summary Links Advertisement Type 4 - AS Boundary Router Summary Link Advertisement Type 5 - AS External Link Advertisement Type 6 - Multicast Group Membership LSA
LSAs contain sequence numbers to detect old and duplicate LSAs.
3232
Metrics (Cost)Metrics (Cost)
Reference RFC 1253
Metric = 10n8 / interface speed
Examples: => 100 Mbps 1 10 Mbps 10 E1 48 T1 65 64 kbps 1562 19.2 kbps 5208 9.6 kbps 10416
3333
Generic Packet FormulaGeneric Packet Formula
DADA SASA TFTF CRCCRCIP DataIP DataIP Header IP Header Protocol ID 89Protocol ID 89
Version Type Packet Length
Router ID
Area ID
Checksum Authentication Type
Authentication
LSA Specific1 – Hello, 2 – DB Description, 3 – LS Request,
4 – LS Update, 5 – LS Ack
3434
The Hello ProtocolThe Hello Protocol
Routers send periodic Hello messages to each other. The packet contains:
The router’s selection of the DR and BDR Router’s priority used to determine the DR and BDR Configurable timers that include:
Hello Interval – To determine when you should hear from a neighbor
RouterDeadInterval – The period before a router is declared down A list of neighbors the router has heard from
This can be turned off by setting the network to an NBMA. This is useful when there is only one router on the cable segment
AA BB CC DDBackupBackupDRDR
DesignatedDesignatedRouterRouter
CC BB 3030 1515 CC BB 8989 AA MCMC
3535
AdjacencyAdjacency
Hello
Hello DR = RT2
D-D Seq = x M, Master
D-D Seq = y M, Master
D-D Seq = y M, Slave
D-D Seq = y+1 M, Master
D-D Seq = y+1 M, Slave
D-D Seq = y+n, Master
D-D Seq = y+n, SlaveLS RequestLS UpdateLS RequestLS UpdateLS AckLS Ack
Down
ExStart
Exchange
Loading
Full
Down
ExStart
Exchange
Loading
Full
Router 1Router 1 Router 2Router 2Designated RouterDesignated Router
3636
Maintaining the DatabaseMaintaining the Database
After Dykstra runs, the database is checked for consistency.
Uses the flooding procedure: Receive an LSA Check for the information in the database Determine whether or not to forward this LSA to an adjacency
Reliability checked using an acknowledgment procedure.
Each LSA contains an age entry.
Sequence numbers are generated for every LSA.
3737
OSPF AreasOSPF AreasAS 1AS 1
Area 0Area 0
BackboneBackboneRouterRouter
BackboneBackboneRouterRouter
BackboneBackboneRouterRouter
Could be a RIPCould be a RIPnetwork within the network within the same domain as OSPFsame domain as OSPF
Area 1Area 1 Internal Internal RouterRouterArea 2Area 2
ASBRASBR
Area Area BorderBorderRouterRouter
3838
The Backbone AreaThe Backbone Area
There must be at least one area in an OSPF network. It is called the backbone area.
Designated by area ID of 0.0.0.0.
Primarily responsibility to propagate information between areas.
Has the same attributes as any other area.
Any network topology may make up the backbone.
It can be used as a real network with attachments.
3939
The Area Border Router (ABR)The Area Border Router (ABR)
Connects an area (or areas) to the backbone.
Summarizes its area topology to the backbone.
Propagates summarized information from the backbone into its area.
Final router that receives an area’s LSA. ABRs do not flood LSA information into the backbone Only produces summaries to the backbone for the backbone to propagate to
other areas
Uses the network summary LSA.
Summarized information is propagated in an area by the DR and its adjacencies.
4040
Virtual LinkVirtual Link
ABRABR ABRABR
Virtual LinkVirtual Link
Area 2.2.2.2Area 2.2.2.2 Area 1.1.1.1Area 1.1.1.1 Backbone AreaBackbone Area
4141
Inter-Area RoutingInter-Area Routing
Area 1Area 1Area 2Area 2
Area BorderRouter
AS 1AS 1
Area 0Area 0
BackboneRouter
BackboneRouter
BackboneRouter
Could be a RIPnetwork within the same domain as OSPF
ASBR
4242
Information from other Autonomous Information from other Autonomous SystemsSystems
Uses the ASBR.
Other ASs according to OSPF may simply be a RIP network within the same OSPF domain.
External LSA used.
Type 1 – The preferred route and used when considering the internal cost of the AS.
Type 2 – Advertising the same metric as was advertised by the ASBR.
These are used to calculate the shortest path to the ASBR.
4343
Stub AreasStub Areas
An area that has only one entry and one exit point (must be the same area).
Used to reduce the number of external advertisements.
A stub area blocks AS external link advertisements.
Area 1Area 1 Area 2Area 2
Area 0Area 0
AS 2AS 2
Contains AS2Contains AS2route entriesroute entries
Does not Does not contain AS2contain AS2route entriesroute entries
4444
RFCs Related to OSPFRFCs Related to OSPF
2178 DS: J. Moy, “OSPF Version 2,” 07/22/97 (211 pages) (.txt format) (obsoletes RFC 1583).
2154 ES: M. Murphy, B. Badger, A. Wellington, “OSPF with Digital Signatures,” 06/16/97 (29 pages) (.txt format).
1850 DS: F. Baker, R. Coltun, “OSPF Version 2 Management Information Base,” 11/03/95. (80 pages)
(.txt format) (Obsoletes RFC 1253).
1793 PS: J. Moy, “Extending OSPF to Support Demand Circuits,” 04/19/95 (31 pages) (.txt format).
1765 E: J. Moy, “OSPF Database Overflow,” 03/02/95 (9 pages) (.txt format).
1745 PS: K. Varadhan, S. Hares, Y. Rekhter, “BGP4/IDRP for IP—OSPF Interaction,” 12/27/94 (19 pages) .txt format).
1587 PS: R. Coltun, V. Fuller, “The OSPF NSSA Option,” 03/24/94 (17 pages) (.txt format).
1586 I: O. deSouza, M. Rodrigues, “Guidelines for Running OSPF Over Frame Relay Networks,”
03/24/94 (6 pages) (.txt format).
1585 I: J. Moy, “MOSPF: Analysis and Experience,” 03/24/94 (13 pages) (.txt format).
1584 PS: J. Moy, “Multicast Extensions to OSPF,” 03/24/94 (102 pages) (.txt, .ps formats).
1403 PS: K. Varadhan, “BGP OSPF Interaction,” 01/14/93 (17 pages) (.txt format) (obsoletes RFC 1364).
1370 PS: Internet Architecture Board, “Applicability Statement for OSPF,” 10/23/92 (2 pages) (.txt format).
4545
Static versus Dynamic RoutingStatic versus Dynamic Routing Entries in a routing table can be static (manually entered by the network administrator) or
dynamic (learned through a routing protocol such as RIP).
Static entries: In the workstation for either:
Default Gateway (router) - used by indirect routing Place a static route in for one that is not learned through RIP, etc.
In the router: Entered as 0.0.0.0 and the next hop (no subnet) to indicate a default route Routers can broadcast this information to their networks to let everyone know which is
the default router A default router is one that all other look to for networks that are not in their tables
Static routes can be used to increase security on the network Any IP network address can be manually entered into the routing table The router administrator supplies:
IP Network address Subnet mask Next hop interface (the IP address of the next routers interface to get to the
network)
4646
Remote NetworksRemote Networks
T3T3T3T3
AAZZ
T1T1CaliforniaCalifornia
VirginiaVirginia
TexasTexas
T1T1 == 1.544Mbps1.544MbpsT3T3 == 45Mbps45Mbps
4747
Datagram RoutingDatagram Routing
PCPC
Host - 129.1.1.1Host - 129.1.1.1
RouterRouter
AA
BB
CC
DDEE
Host - 129.1.1.2Host - 129.1.1.2
129.1.1.3129.1.1.3
129.2.1.1129.2.1.1
129.2.1.2129.2.1.2
CC DD 08000800 129.2.1.2129.2.1.2 129.1.1.2129.1.1.2 IP DataIP Data CRCCRC
BB AA 08000800 129.2.1.2129.2.1.2 129.1.1.2129.1.1.2 IP DataIP Data CRCCRC
DADA SA SA TF TF Data Data CRCCRC
IP IP HeaderHeader
IP IP HeaderHeader