Download TDC 563-98-301/302, Spring 2002 2-14 TDC 563-98

Unit 2: Interior Routing Protocols: RIP
and OSPF
• Introduction to Cisco Router Configuration
• RIP
– RIP-1 v.s. RIP-2
– RIP for IPv6
• OSPF
– Review of link state routing
– Modified Dijkstra’s algorithm for finding multiple paths
– Packet types
• LSA (Link state advertisements)
• Lollipop Sequence number
• OSPF for IPv6 (Section 6.7. Read on your own)
TDC 563-98-301/302, Spring 2002
2-1
Cisco Router Configuration
Glossary Of Terms And Acronyms
Cisco IOS - Cisco Internetworking Operating System
CLI - Command Line Interface
EXEC - Command line session to the router (could be console,
modem, or telnet)
Flash - Non-Volatile Memory used to store IOS software image
NVRAM- Non-Volatile RAM used to store router configuration
RAM - Random Access Memory
TDC 563-98-301/302, Spring 2002
2-2
CLI Architecture
• CLI
can be accessed through one of the following
• console connection
• modem connection, or
• a telnet session.
• referred to as an EXEC session
• user EXEC level – limited amount of basic monitoring
• privileged EXEC level – access all router commands, including critical commands
such as configuration and management.
Router> enable
Password: [enable password]
Router#
disable Router>
TDC 563-98-301/302, Spring 2002
2-3
Global Command: A single-line
command that affects the function of
the whole unit
Configuration mode
Major Command: A command
that indicates a particular
interface or process that is
being configured. It must be
followed by subcommands.
TDC 563-98-301/302, Spring 2002
Subcommand: used after a major
command to configure a process or
interface
2-4
CLI Editor Features
Context Sensitive Help
• question mark (?) to get help
• Word help - obtain a list of commands that begin with a particular character
sequence. Example:
Router# co?
configure connect copy
• Command syntax help - obtain a list of command, keyword, or argument
options that are available based on the syntax the user has already entered.
Enter a question mark (?) in the place of a keyword or argument.
Example:
Router# configure ?
memory
Configure
network
Configure
overwrite-network Overwrite
terminal
Configure
<cr>
TDC 563-98-301/302, Spring 2002
from NV memory
from a TFTP network host
NV memory from TFTP network host
from the terminal
2-5
Command Syntax Check
• router will inform the user and indicate where the syntax error has occurred. A
caret symbol (^) will appear underneath the incorrect command, keyword, or
argument. Example:
Router(config)#interface ethernat
^%
Invalid input detected at '^' marker.
Command Abbreviation
Commands and keywords can be abbreviated to the minimum number of
characters that identifies a unique selection. For example, you can abbreviate the
"configure" command to "conf" because "configure" is the only command that
begins with "conf". You could not abbreviate the command to "con" because
more than one command could fit this criteria. The router will issue the
following error message if you do not supply enough characters.
cisco(config)#I
% Incomplete command
TDC 563-98-301/302, Spring 2002
2-6
Hot Keys
(See more on page 13
in the text)
Backspace
- Removes one character to the left of the cursor.
TAB
- Finishes a partial command.
Ctrl-A
- Moves the cursor to the beginning of the current
line.
Ctrl-R
- Redisplays a line.
Ctrl-U
- Erases a line.
Ctrl-W
- Erases a word.
Ctrl-Z
- Ends configuration mode and returns to the EXEC.
Up Arrow
- Allows user to scroll forward through former
commands.
- Allows user to scroll backward through former
commands.
Down
Arrow
TDC 563-98-301/302, Spring 2002
2-7
Router Configuration
Entering Configurations: An example
Router> enable
- switches to privileged EXEC level
Router# configure terminal
- switches to global configuration level
Router(config)# enable secret cisco
- configures router with an enable secret (global)
Router(config)# ip route 0.0.0.0 0.0.0.0 20.2.2.3
- configures a static IP route (global)
Router(config)# interface ethernet0
- switches to configure the ethernet0 interface
Router(config-if)# ip address 10.1.1.1 255.0.0.0
- configures an IP address on ethernet0 (interface)
Router(config-if)# no shutdown
- activates ethernet0 (interface)
Router(config-if)# exit
- exits back to global configuration level
Router(config)# interface serial0
- switches to configure the serial0 interface
Router(config-if)# ip address 20.2.2.2 255.0.0.0
- configures an IP address on serial0 (interface)
Router(config-if)# no shutdown
- activates serial0 (interface)
Router(config-if)# exit
- exits back to global configuration level
Router(config)# router rip
- switches to configure RIP routing engine
Router(config-router)# network 10.0.0.0
- adds network 10.0.0.0 to RIP engine (routing engine)
Router(config-router)# network 20.0.0.0
- adds network 20.0.0.0 to RIP engine (routing engine)
Router(config-router)# exit
- exits back to global configuration level
Router(config)# exit
- exits out of configuration level
Router# copy running-config startup-config
- saves configuration into NVRAM
Router# disable
- disables privileged EXEC level
Router>
- indicates user is back to user EXEC level
TDC 563-98-301/302, Spring 2002
2-8
Table 3.1 in text
Command
Description
Configure
terminal
Executes configuration commands from the
terminal. Use this command to make changes to the
configuration file from the console port or a telnet
session. Once changes are entered, press <Ctrl-Z>
to end the update mode session.
Configure
memory
Executes configuration commands stored in
NVRAM
Configure
network
Retrieves configuration commands are stored in a
network server and load that configuration into
memory. You will be prompted for the IP address of
the TFTP (Trivial FTP) server to connect to, as well
as the configuration filename.
TDC 563-98-301/302, Spring 2002
2-9
Removing Commands / Resetting Default Values
navigate to the proper location and type "no" followed by the command to be removed.
Router> enable
Router# configure terminal
Router(config)# interface ethernet0
Router(config-if)# no ip address
Router(config-if)# exit
Router(config)# exit
Router# disable
Router>
- switches to privileged EXEC level
- switches to global configuration level
- switches to configure the ethernet0 interface
- removes IP address
- exits back to global configuration level
- exits out of configuration level
- disables privileged EXEC level
- prompt indicates user is back to user EXEC level
Some configuration commands in IOS are enabled by default and assigned a certain default
value. When left at the default value, these commands will not be displayed when the
configuration is listed. If the value is altered from the default setting, issuing a "no" form of the
command will restore the value to the default setting.
TDC 563-98-301/302, Spring 2002
2-10
Saving Configurations
•configurations in two locations - RAM and NVRAM.
•The running configuration is stored in RAM.
•Any configuration changes to the router are made to the running-configuration and take
effect immediately after the command is entered.
•The startup-configuration is saved in NVRAM and is loaded into the router's runningconfiguration when the router boots up.
• To save the running-configuration to the startup configuration, type the following from
privileged EXEC mode (i.e. at the "Router#" prompt.)
Router# write mem
TDC 563-98-301/302, Spring 2002
2-11
Router Management
Some common commands for displaying information.
Displaying Configurations
Router#sh conf
- show NVRAM configuration
Router#wri term
- Display running
configuration
Displaying Software Version And More
Software Version
- IOS software version (stored in flash)
Bootstrap Version
- Bootstrap version (stored in Boot ROM)
System up-time
- Time since last reboot
System restart info - Method of restart (e.g. power cycle,
crash)
Software image name - IOS filename stored in flash
Router Type and Processor type
- Model number and
processor type
Memory type and allocation (Shared/Main) - Main = Processor RAM
- Shared = Packet I/O buffering
Software Features
- Supported protocols / feature sets
Hardware Interfaces - Interfaces available on router
Configuration Register - Bootup specifications, console speed
setting, etc.
TDC 563-98-301/302, Spring 2002
2-12
Example output of Router#wri
TDC 563-98-301/302, Spring 2002
term
2-13
TDC 563-98-301/302, Spring 2002
2-14
Displaying Interface States
To view information about a particular interface, use the show interface command. The show
interface command provides the following list of important information:
Interface State (e.g. UP, DOWN, LOOPED)
Protocol addresses
Bandwidth
Reliability and Load
Encapsulation type
Packet Rates
Error Rates
Signaling Status (i.e. DCD,DSR,DTR,RTS,CTS)
TDC 563-98-301/302, Spring 2002
2-15
TDC 563-98-301/302, Spring 2002
2-16
RIP1 (RFC 1058) and (RFC 1388) RIP2

distance-vector protocol using hop-count as metric

infinity value is 16 hops

announces (distance vectors) sent to neighbors every 30 seconds; time
out in 180 sec every

split horizon with poisoned reverse

encapsulated in UDP: Well known port 520

Included in RIP-maintained routing table:
- address of (net/subnet/host) destination
- metric associated with destination 2
- address of next hop router
- recently-updated flag-updated flag
- several timers several timers FC
TDC 563-98-301/302, Spring 2002
2-17
RIP-1 Message Format
Supposed to support a variety
of protocols. But in practice
only TCP/IP uses it.
Figure 13-8 Response message
TDC 563-98-301/302, Spring 2002
2-18
RIP-2
•compatible upgrade to RIP v1 including subnet routing, authentication, CIDR
aggregation, route tags and multicast transmission t
•RFC 2453 includes background and protocol definition
Subnet Support
•RIP-1 supports subnet routes only within the subnetted network (suing single subnet
mask)
•RIP-2 includes subnet mask in the messages. This allows for subnet knowledge outside
subnet
Distinguish
•More convenient partitioning using variable-length subnets
TDC 563-98-301/302, Spring 2002
multiple domains
running on the
same wire/subnet
2-19
Routing per subnet
10.1.0.0
(255.255.0.0)
A
B
 10.0.0.0
(255.0.0.0)
E
F
 10.0.0.0
(255.0.0.0)
C
D
10.2.0.0
(255.255.0.0)
TDC 563-98-301/302, Spring 2002
2-20
Next Hop
Authentication
RIP-1 is completely not secure; anyone can act as a router just by
sending RIP-1 messages (e.g. advertise cost 0 and everyone will use that
route)
RIP-2 supports generic notion of authentication, but only “password” is
defined so far. Still not very secure.
At least prevents some “accidents” reasonably well
TDC 563-98-301/302, Spring 2002
2-21
Authentication
TDC 563-98-301/302, Spring 2002
2-22
Variable-length subnetting
TDC 563-98-301/302, Spring 2002
2-23
Multicasting
Broadcast on a local link will be sent to all nodes including hosts
RIP-2 uses 224.0.0.9 – Multicast address to routers only
3 modes:
oSend RIP-1 packets in broadcast mode - When most routers are not yet
upgraded)
oSend RIP-2 packets in broadcast mode - When some routers are still RIP-1)
oSend RIP-2 packets in multicast mode – When all routers are upgraded to RIP-2
RIPng for IPv6
Almost the same as IPv6 except
The use of Ipv6 security instead of RIPv2 authentication entries
Change in the packet formats in order to carry the longer Ipv6 addresses
(Skip section 5.6)
TDC 563-98-301/302, Spring 2002
2-24
Some Cisco commands related to configuration of RIP
• router1 (config)# router rip
enable rip routing process
router1 (config-router) network A.B.C.D
• router1 (config-router)# passive interface S0 stop router sending updates
through this interface
• router1 (config-router)#neighbor W.X.Y.Z
allow updates to be sent to a
neighbor connected by a
non-broadcast network
• router1# show ip route
• router1# show ip protocol
TDC 563-98-301/302, Spring 2002
2-25
Link State Routing
• Dynamic
• Sharing knowledge about the neighborhood- link states: who I am
directly connected to and the distance (based on minimum delay,
maximum throughput, cost, hop counts etc.)
• Sharing with every other router – broadcast by flooding
• Sharing when there is a change
• OSPF (Open Shortest Path First), the newer Internet routing protocol is
an example.
• General steps
–
–
–
–
–
Hello: discovering reachability
Build link state packets (advertisements)
Broadcast the link state packets: initially and when there are changes
Build a map from the received link state packets
From the map calculate the shortest path
TDC 563-98-301/302, Spring 2002
2-26
Multiple metrics
Can support fine-grained metrics (vs. RIP)
Multiple metrics
oThroughput, Delay, Cost, Reliability
Can computer a different routing table for each metric.
OSPFv2 supports an extension that allows the metric to be used specified in the
packet.
OSPF: Areas within an AS
•Backbone router: connect only to the backbone area (Area 0)
•Area border router: attaches to multiple areas.
•Internal router: all interfaces connected to the same area.
•AS boundary router: connect to other ASes
TDC 563-98-301/302, Spring 2002
2-27
Area 0
Example Cisco
configuration:
Router1 e0/0 120.1.1.1
Router2 e0/0 120.1.1.2
Router2 e0/1 150.1.1.1
Area 1
Router3 e0/0 150.1.1.2
OSPF process ID
Router1:
Router1(config)# router ospf 10
Router1(config-router)# network 120.0.0.0 0.255.255.255 area 0
Wildcard mask: like an inverse subnet mask
Router2:
Router2(config)# router ospf 10
Router2(config-router)# network 120.0.0.0 0.255.255.255 area 0
Router2(config-router)# network 150.1.0.0 0.0.255.255 area 1
Router3:
Router3(config)# router ospf 10
Router3(config-router)# network 150.1.0.0 0.0.255.255 area 1
TDC 563-98-301/302, Spring 2002
2-28
Point-to-point link
TDC 563-98-301/302, Spring 2002
2-29
Transient link
Stub link
Virtual link: When the link between two routers is broken, a virtual link can
be created to go through other routers (usually more than one).
TDC 563-98-301/302, Spring 2002
2-30
An Example Internet
Graphical
representation of the
internet
5
TDC 563-98-301/302, Spring 2002
5
2-31
Dijkstra’s Algorithm
1.
Initialize the set E to contain only the source node S and R to contain all
other nodes. Initialize the list of paths O to contain the one segment paths
starting from S. Each of these paths has a cost equal to the corresponding
link’s metric. Sort list O by increasing metrics.
2.
If list O is empty, or if the first path in O has an infinite metric, mark all
nodes left in R as unreachable. The algorithm has terminated.
3.
First examine P. the shortest path in list O. Remove P from O. Let V be
the last node in P. If V is already in set E, continue at step 2. Otherwise, P
is the shortest path to V. Move V from R to E.
4.
Build a set of new candidate paths by concatenating P and each of the
links starting from V. The cost of these paths is the sum of the cost of P
and the metric of the link appended to P. Insert the new links in the
ordered list O, each at the rank corresponding to its cost. Continue at step
2.
TDC 563-98-301/302, Spring 2002
2-32
Permanent (E) (each cell
includes the entries in the
previous rows)
A
Tentative (R)
Paths (O)
N1 [A  N1 (5)]
B, C, D, E, F, N1, N2, N3, N4,
N5
B, C, D, E, F, N2, N3, N4, N5
B [A N1B (5)]
C, D, E, F, N2, N3, N4, N5
C [A N1C (5)]
D, E, F, N2, N3, N4, N5
N2 [AN1CN2 (7)]
D, E, F, N3, N4, N5
D [AD (8)]
E, F, N3, N4, N5
E [AN1BE (10)]
F, N3, N4, N5
N3 [ADN3 (10)]
F, N4, N5
Shortest path already exists to E
F, N4, N5
F [ADN3F (10)]
N4, N5
N4 [AN1BEN4 (12)]
N5
Shortest path already exists to
N3
N5[ADN3FN5 (15)]
N5
A  N1 (5)
A D (8)
AN1B (5)
AN1C (5)
AD (8)
AN1C (5)
AD (8)
AN1BE (10)
AN1CN2 (7)
AD (8)
AN1BE (10)
AD (8)
AN1BE (10)
AN1BE (10)
ADN3 (10)
ADN3 (10)
AN1BEN4 (12)
AN1BEN3 (15)
ADN3E (10)
ADN3F (10)
AN1BEN4 (12)
AN1BEN3 (15)
ADN3F (10)
AN1BEN4 (12)
AN1BEN3 (15)
AN1BEN4 (12)
AN1BEN3 (15)
ADN3FN5 (15)
AN1BEN3 (15)
ADN3FN5 (15)
ADN3FN5 (15)
TDC 563-98-301/302, Spring 2002
2-33
Multiple paths using a modification of Dijkstra’s Algorithm (Equal Cost)
1.
Initialize the set E to contain only the source node S and R to contain all other
nodes. Initialize the list of paths O to contain the one segment paths starting
from S. Each of these paths has a cost equal to the corresponding link’s metric.
Sort list O by increasing metrics.
2.
If list O is empty, the algorithm has terminated.
3.
First examine P. the shortest path in list O. Remove P from O. Let V be the last
node in P. If V is already in set E, check continue at step 4. Otherwise, P is the
shortest path to V. Move V from R to E. Continue at step 5.
4.
If the metric of path P between S and V is equal to the previously computed
distance between S and V, we have found an “equal cost path” to V. If it is
larger, we should ignore P. In all cases, continue at step 2.
5.
Build a set of new candidate paths by concatenating P and each of the links
starting from V. The cost of these paths is the sum of the cost of P and the
metric of the link appended to P. Insert the new links in the ordered list O, each
at the rank corresponding to its cost. Continue at step 2.
TDC 563-98-301/302, Spring 2002
2-34
Permanent (E) (each cell
includes the entries in the
previous rows)
A
Tentative (R)
Paths (O)
N1 [A  N1 (5)]
B, C, D, E, F, N1, N2, N3, N4,
N5
B, C, D, E, F, N2, N3, N4, N5
B [A N1B (5)]
C, D, E, F, N2, N3, N4, N5
C [A N1C (5)]
D, E, F, N2, N3, N4, N5
N2 [AN1CN2 (7)]
D, E, F, N3, N4, N5
D [AD (8)]
E, F, N3, N4, N5
E [AN1BE (10)]
F, N3, N4, N5
A  N1 (5)
A D (8)
AN1B (5)
AN1C (5)
AD (8)
AN1C (5)
AD (8)
AN1BE (10)
AN1CN2 (7)
AD (8)
AN1BE (10)
AD (8)
AN1BE (10)
AN1BE (10)
ADN3 (10)
ADN3 (10)
AN1BEN4
AN1BEN3
ADN3E (10)
ADN3F (10)
AN1BEN4
AN1BEN3
ADN3F (10)
AN1BEN4
AN1BEN3
AN1BEN4
AN1BEN3
ADN3FN5
AN1BEN3
ADN3FN5
ADN3FN5
N3 [ADN3 (10)]
F, N4, N5
E [ADN3E (10)]
(An additional shortest path. Do
not expand)
F [ADN3F (10)]
F, N4, N5
N4 [AN1BEN4 (12)]
N5
The above path to N3 is longer
than the existing shortest path 
ignore
N5[ADN3FN5 (15)]
N5
TDC 563-98-301/302, Spring 2002
N4, N5
(12)
(15)
(12)
(15)
(12)
(15)
(12)
(15)
(15)
(15)
(15)
(15)
2-35
OSPF Packet Types
•Hello: Establishes and maintains neighbor relationships.
•Database Description: When a router just came up, it cannot wait for all link
state packets. Neighbors will send it a database description (not the full database
but like an outline). From this, the router can then ask for information it does not
have. Describes the contents of the topological database.
•Link-state Request: Requests pieces of the topological database from neighbor
routers. These messages are exchanged after a router discovers (by examining
database-description packets) that parts of its topological database are out of
date.
•Link-state Update: Responds to a link-state request packet. These messages
also are used for the regular dispersal of LSAs. Several LSAs can be included
within a single link-state update packet.
•Link-state Acknowledgment: Acknowledges link-state update packets.
TDC 563-98-301/302, Spring 2002
2-36
Link-state advertisement types
•Router Links (RL) are generated by all routers. These links describe the state of
the router interfaces inside a particular area. These links are only flooded inside the
router's area.
•Network Links (NL) are generated by a DR (Designated Router) of a particular
segment; these are an indication of the routers connected to that segment.
•Summary Links (SL) are the inter-area links (type 3); these links will list the
networks inside other areas but still belonging to the autonomous system. Summary
links are injected by the ABR (Area Border Router) from the backbone into other
areas and from other areas into the backbone. These links are used for aggregation
between areas.
•Asbr-summary links are type 4 links that point to the ASBR (Autonomous System
Boundary Router). This is to make sure that all routers know the way to exit the
autonomous system.
•External Links (EL), these are injected by the ASBR into the domain.
TDC 563-98-301/302, Spring 2002
2-37
Router Link – defines the links of a true router
Router Link LSA (6.5.2 in text)
= 1  ExternalRoutingCapability
(eg. Non-stop area, backbone etc.)
= 1  Border Router
(Details later)
(Depends on type of link)
(Depends on type of link)
(Default)
(Type of Service)
TDC 563-98-301/302, Spring 2002
2-38
Link Type
Type 1: Pointto-point
connection to
another router
Type 2:
Connection to
any-to-any
network
Type 3:
Connection to
stub network
Type 4:
Virtual link
TDC 563-98-301/302, Spring 2002
Link Identification
Address of neighbor
router
Link Data
Interface number
Address of designated
router
Router address
Network address
Network mask
Address of neighbor
router
Router address
2-39
Network link – defines the links of a network.
Network links (6.5.3 in text)
(All attached routers)
TDC 563-98-301/302, Spring 2002
2-40
Summary link to network
Summary link to AS
boundary router
TDC 563-98-301/302, Spring 2002
2-41
Summary links (6.5.4 in text) to network or to AS boundary router
or Type: 4
(All 0’s for type 4)
External link
TDC 563-98-301/302, Spring 2002
2-42
External links (6.5.5 in text)
(May provide a better route)
(Used by other protocols)
Multiple Areas:
Example
TDC 563-98-301/302, Spring 2002
2-43
LSA (Link State Advertisement) header
Link state age: # of sec since the message is generated
E flag: set to 0 for a stub area. E stands for external capability
T flag: set if the router can handle multiple types of service
Link state ID: Depends on the link state type. Usually an IP address of a router or network.
Advertising router: IP address of the advertising router
Link state checksum: cover the entire packet except for the age field
Length: Length of the whole packet in bytes
TDC 563-98-301/302, Spring 2002
2-44
Problem: router failure
• A failed router and comes up but does not remember the last sequence number it
used before it crashed
• New LSPs may be ignored if they have lower sequence number (sequence
number wraps around)
 One solution: LSP Aging
• Nodes periodically decrement age of stored LSPs
• LSPs expire when TTL reaches 0
– LSP is re-flooded once TTL = 0
• Rebooted router waits until all LSPs have expired
• Trade-off between frequency of LSPs and router wait after reboot
– Age too small  frequent updates
– Age too large  router wait long time on rebooting
TDC 563-98-301/302, Spring 2002
2-45
 A better solution: Lollipop sequence space
Let N = 232/2 = 231. Divide sequence space into 3 spaces:
– -N + 1 to 0 (negative space)
– 0 to N-2 (positive space)
– -N and N-1 (illegal)
• Router comes up and starts with –N+1, then –N+2 etc.
• When seq number becomes positive, wrap around and stay in the positive space
• Suppose a < b:
 a is older than b if:
–a<0
– a > 0 and b - a < (N-1)/2, (i.e., smaller than a half circle)
 a is newer otherwise
TDC 563-98-301/302, Spring 2002
2-46
Lollipop cont.
• Newly booted router always starts with oldest seq num (-N + 1)
• New rule:
– if router R1 gets older LSP from router R2, R1 informs R2 of the seq
number in R1’s LSP
• Newly booted router discovers its seq number before it crashed and resumes
• Aging still needed to flush out old states:
– suppose a router is down but not detected
– net partitions and then heals
TDC 563-98-301/302, Spring 2002
2-47