Overview of
Dynamic Routing Protocols
CIT 340
Overview of Routing Protocols
Exterior
Gateway
Protocols
Interior Gateway Protocols
Distance Vector
Routing Protocols
Classful
Classless
IPv6
IGRP
EGP
(1982/1988)
(1985)
(1982)
RIPv2
EIGRP
OSPFv2
IS-IS
BGPv4
(1994)
(1992)
(1991)
(1990)
(1995)
RIPng
EIGRP for
IPv6
OSPFv3
IS-IS for
IPv6
BGPv4
for IPv6
(2000)
(1999)
(not yet
released)
•
Path
Vector
RIPv1
(1997)
•
Link State Routing
Protocols
(1999)
Note: IGRP and EIGRP are Cisco proprietary protocols. They are meant as an alternative between
the limited RIP routing protocol and the more complicated and resource intensive OSPF and IS-IS
routing protocols. IGRP was discontinued with IOS 12.2 in 2005.
The dates shown are when the RFC or other document was finalized. The protocol may have been
implemented earlier than this date.
2
The Routing Protocols we will focus on
Exterior
Gateway
Protocols
Interior Gateway Protocols
Distance Vector
Routing Protocols
Classful
Classless
IPv6
Link State Routing
Protocols
Path
Vector
RIPv1
IGRP
EGP
(1982/1988)
(1985)
(1982)
RIPv2
EIGRP
OSPFv2
IS-IS
BGPv4
(1994)
(1992)
(1991)
(1990)
(1995)
RIPng
EIGRP for
IPv6
OSPFv3
IS-IS for
IPv6
BGPv4
for IPv6
(2000)
(1999)
(1997)
(not yet
released)
(1999)
• Note: RIPv2 will not be discussed in detail but will be used as an
example of transitioning from a classful to a classless routing protocol.
3
Dynamic Routing Protocol Basics
• Routing Protocol = A language a router speaks with other routers to
•
share information about the reachability and status of networks.
Routing protocols perform:
– Best-path determination
– Route-table-update functions
– Next-best path should the best-path become unusable
4
Algorithms
• All dynamic routing protocols are built around an
•
•
algorithm.
Algorithm = Step-by-step procedure for solving a
problem.
At a minimum the algorithm must specify:
– A procedure for passing reachability information
about networks to other routers.
– A procedure for receiving reachability information
from other routers.
– A procedure for determining optimal routes based
on the reachability information it has and for
recording this information in a route table.
– A procedure for reacting to, compensating for, and
advertising topology changes in a network.
A tribute to alKhwarizmi, 9th
century Persian
mathematician, the
originator and
namesake of
algorithms.
5
Algorithms
Distance Vector Routing Protocols
• RIP, IGRP:
– Variant of Bellman-Ford (or Ford-Fulkerson)
• EIGRP:
– Diffusing Update Algorithm (DUAL) first
proposed by E.W. Dykstra and C.S. Scholten
– Latest and most prominent work done by J.J.
Garcia-Luna Aceves (UC Santa Cruz)
Link State Routing Protocols
• OSPF, IS-IS:
– Dijkstra’s SPF (Shortest Path First) algorithm,
E.W. Dijkstra
6
Path Determination
192.168.10.1
Serial 0 255.255.255.252
Ethernet 0
172.16.1.1
255.255.255.0
MAC: 0cddeeffaabb
Ethernet 1
172.16.2.1
255.255.255.0
MAC: 0abbccddeeff
• Router interfaces must be members of different networks.
• Router interfaces participate in the network like other hosts on that
•
network.
Ethernet interfaces:
– Have MAC Addresses
– ARP Tables
– Participate in the ARP Request and ARP Reply process like other
hosts on that network.
7
Path Determination
?
Routing
Updates
Simplistic questions illustrating the complexity of routing protocols:
• What should Router A do with the routing updates from B and C?
• What mechanism is used to ensure that all routers receive all routing
information?
• If Router A has hears about 192.168.4.0/24 from B and C which router
should be the next hop used to reach that network? Should both be
used?
• What metric is used to determine best path?
8
Metrics
• Metric = A variable assigned to
routes as a meaning of ranking
them from best to worst or from
most preferred to least
preferred.
– Hop count
– Bandwidth
– Delay
– Reliability
– Load
– Cost
• RIP
•
•
•
•
– Hop count
IGRP and EIGRP
– Bandwidth
– Delay
– Reliability
– Load
OSPF
– Cost (Cisco defines cost as
Bandwidth)
IS-IS
– Default (Cisco supported)
– Delay
– Expense
– Error
BGP
– Policies and Attributes
9
Convergence
•
Convergence = The process of bringing all route tables to
a state of consistency.
Convergence
Vegetarian Catering
10
Convergence
• During the time it takes for convergence to occur, routers will continue
•
•
•
to route packets using their current routing tables.
It is during this time that routing errors may occur.
Therefore, convergence time is an important factor in any routing
protocol.
The faster a network can reconverge after a topology change, the
better.
11
Distance Vector Routing Protocols
•
•
•
Most routing protocols fall into one of two classes:
1. Distance Vector
2. Link State
Distance Vector = Derived from the fact that routes are advertised as
vectors of (distance, direction), where distance is defined in terms of a
metric and direction is defined in terms of the next-hop router.
Built around Bellman-Ford algorithm.
Serial 0
Ethernet 0
Distance
Distance
Ethernet 1
Distance
12
Distance Vector Routing Protocols
•
•
Distance Vector Routing Protocols include:
– RIP for IP
– XNS (Xerox Networking System’s) RIP
– Novell’s IPX RIP
– Cisco’s IGRP
– Cisco EIGRP
– DEC’s DNA Phase IV
– AppleTalks Routing Table Maintenance Protocol (RTMP)
Only RIP for IP and EIGRP are current routing protocols.
13
Distance Vector Routing Protocols
Periodic updates
Common Characteristics (generalization)
• Periodic Updates
– RIP’s 30 seconds to IGRP’s 90 seconds. (Notable exception is
EIGRP)
• Neighbors
– Sharing a common data link or higher-level adjacency.
• Broadcast updates
– Sends updates to a broadcast IP address (Some protocols use
multicast addresses)
• Full Routing Table Updates
– Tell their neighbors everything they know by sending their entire
routing table.
14
Routing by Rumor
15
Distance Vector
Techniques Review
Event-driven or triggered updates
• Route Invalidation Timers
•
•
•
•
•
– “If I don’t hear from you within a certain time period I will invalidate
you and your routes.”
Split Horizon and Split Horizon with Poison Reverse
– “I don’t need to tell you since you are the one who told me.”
Counting to Infinity and Setting a Maximum
– “In case there is a routing loop being created, I will set a maximum
metric and then declare the route unreachable.”
Triggered Updates or Flash Updates
– “As soon as I hear a change, I will let my other neighbors know.”
Holddown Timers
– “I’m skeptical of this new “poorer” information and will wait to see if
convergence is in the works.”
Asynchronous Updates and Timing Jitter
– “So we all don’t talk at once, we’ll each wait a certain random time.”
16
Routing by Rumor
•
Distance vector routing
protocols provide road signs
to networks.
17
As opposed to Link State Routing Protocols
•
Link state routing
protocols provide
road maps to
networks (next).
18
Link State Routing Protocols
• Link state routing protocols sometimes
•
•
called:
– Shortest Path First (SPF) protocol
– Distributed Database protocol
Built around algorithm from graph
theory, E.W. Dijkstra’s short path
algorithm.
Link state routing protocols include:
– OSPF
– IS-IS
– DEC’s DNA Phase V (legacy)
– Novell’s Netware Link Services
Protocol (NLSP) (legacy)
19
Link State Routing Protocols
These topics will be discussed in detail during OSPF
• Neighbor and Neighbor Discovery
– Process of discovering neighbors on common
links
• Link State Flooding
– Process of flooding link state information within
a topology
– Link state protocols converge much faster than
distance vector routing protocols when the
topology changes
• Link State Database
– Major part of a link state routing protocol
– Important that routers have common link state
databases
• SPF Algorithm
– Using the link state database, this algorithm is
used to calculate the shortest paths to
networks.
20
Link State Routing Protocols
1 – Flooding of link-state
information
2 – Building a
Topological Database
5 – Routing Table
3 – SPF Algorithm
4 – SPF Tree
21
Interior and Exterior Gateway Protocols
Exterior
Gateway
Protocols
Interior Gateway Protocols
Distance Vector
Routing Protocols
Classful
Classless
IPv6
IGRP
EGP
(1982/1988)
(1985)
(1982)
RIPv2
EIGRP
OSPFv2
IS-IS
BGPv4
(1994)
(1992)
(1991)
(1990)
(1995)
RIPng
EIGRP for
IPv6
OSPFv3
IS-IS for
IPv6
BGPv4
for IPv6
(2000)
(1999)
(not yet
released)
•
Path
Vector
RIPv1
(1997)
•
Link State Routing
Protocols
(1999)
Note: IGRP and EIGRP are Cisco proprietary protocols. They are meant as an alternative between
the limited RIP routing protocol and the more complicated and resource intensive OSPF and IS-IS
routing protocols. IGRP was discontinued with IOS 12.2 in 2005.
The dates shown are when the RFC or other document was finalized. The protocol may have been
implemented earlier than this date.
22
Interior and Exterior Gateway Protocols
• Border Gateway Protocol (BGP) for IP
• Exterior Gateway Protocol (EGP) for IP (yes, an EGP named EGP)
• ISO’s InterDomain Routing Protocol (IDRP)
23
Interior and Exterior Gateway Protocols
• Interior Gateway Protocols = Routing protocols within an
•
•
autonomous system.
Exterior Gateway Protocols = Routing protocols between an
autonomous system.
Autonomous System
– Older definition: Group of routers under a common administrative
domain running a common routing protocol. (Nowadays it is
common the some companies may run multiple routing protocols.)
– Newer definition: A network under a common administration.
– Note: AS might also sometimes refer to a process domain.
24
Redistribution
•
Redistribution is used to route between different IGP
routing protocols.
25
Classful vs. Classless Routing Protocols
26
Classless Routing Protocols
“The true characteristic of a classless routing protocol is the ability to
carry subnet masks in their route advertisements.” Jeff Doyle, Routing
TCP/IP
Benefits:
• All-zeros and all-ones subnets
– - Although some vendors, like Cisco, can also handle this with
classful routing protocols.
• VLSM
– Can have discontiguous subnets
– Better IP addressing allocation
• CIDR
– More control over route summarization
Classless Routing Protocols
Classless Routing Protocols:
• RIPv2
• EIGRP
• OSPF
• IS-IS
• BGPv4
Remember classful/classless routing protocols is different than classful/classless
routing behavior.
Classlful/classless routing protocols (RIPv1, RIPv2, IGRP, EIGRP, OSPF, etc.)
has to do with how routes get into the routing table; how the routing table gets
built.
Classful/classless routing behavior (no ip classless or ip classless) has to do with
the lookup process of routes in the routing table (after the routing table has
been built).
It is possible to have a classful routing protocol and classless routing behavior or
visa versa.
It is also possible to have both a classful routing protocol and classful routing
behavior; or both a classless routing protocol and classless routing behavior.
SantaCruz1
router rip
network 172.30.0.0
network 192.168.4.0
version 2
no auto-summary
RIPv2 Example
Internet
static route to
207.0.0.0/8
10.0.0.0/8
.1
SantaCruz2
router rip
network 172.30.0.0
network 192.168.4.0
version 2
no auto-summary
207.0.0.0/16
207.1.0.0/16
207.2.0.0/16
207.3.0.0/16
etc.
.1 e0
ISP
.25
s0
s1
.21
192.168.4.24/30
192.168.4.20/30
172.30.200.32/28
ISP
router rip
redistribute static
network 10.0.0.0
network 192.168.4.0
version 2
no auto-summary
Lo2
.26
172.30.2.0/24
ip route 207.0.0.0 255.0.0.0 null0
s0
Lo0
.1 SantaCruz1
.1 e0
172.30.1.0/24
s0
.22
Lo1
`
172.30.200.16/28
SantaCruz2 Lo0
.1 e0
.1
172.30.100.0/24
172.30.110.0/24
SantaCruz2#show ip route
C
C
R
R
C
C
R
C
R
R
VLSM and the Routing Table
172.30.0.0/16 is variably subnetted, 6 subnets, 2 masks
172.30.200.32/28 is directly connected, Loopback2
172.30.200.16/28 is directly connected, Loopback1
172.30.2.0/24 [120/2] via 192.168.4.21, 00:00:21, Serial0
172.30.1.0/24 [120/2] via 192.168.4.21, 00:00:21, Serial0
172.30.100.0/24 is directly connected, Ethernet0
172.30.110.0/24 is directly connected, Loopback0
192.168.4.0/30 is subnetted, 2 subnets
192.168.4.24 [120/1] via 192.168.4.21, 00:00:21, Serial0
192.168.4.20 is directly connected, Serial0
Internet
10.0.0.0/8 [120/1] via 192.168.4.21, 00:00:21, Serial0
static route to
207.0.0.0/8 [120/1] via 192.168.4.21, 00:00:21, 10.0.0.0/8
Serial0
207.0.0.0/8
.1
207.0.0.0/16
207.1.0.0/16
207.2.0.0/16
207.3.0.0/16
etc.
.1 e0
ISP
.25
Supernet, classless routing protcols
will route supernets (CIDR)
s0
s1
.21
192.168.4.24/30
192.168.4.20/30
172.30.200.32/28
Lo2
.26
172.30.2.0/24
s0
Lo0
.1 SantaCruz1
.1 e0
172.30.1.0/24
s0
.22
Lo1
`
172.30.200.16/28
SantaCruz2 Lo0
.1 e0
.1
172.30.100.0/24
172.30.110.0/24