Basics of Dynamic Routing
Presented by Aaron Jarvis
Network Engineer
1
Agenda
•Introduction to Dynamic Routing
•Choosing the Right Protocol
•Configuring Dynamic Routing
•How the ITaP Production Data Network uses
dynamic routing
Agenda
•Introduction to Dynamic Routing
•Choosing the Right Protocol
•Configuring Dynamic Routing
•How the ITaP Production Data Network uses
dynamic routing
Introduction to Dynamic Routing
•What is routing?
•How data is forwarded between subnets
•Network Layer or Layer 3 in the OSI Model
•Provides end-to-end reachability
Network
Data Link
Physical
Introduction to Dynamic Routing
•How are routing decisions made?
•Forwarded based on the destination IP address
•Router builds/maintains a routing table
•Current view of the network
•Populated either dynamically or manually
router#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is 192.5.40.54 to network 0.0.0.0
69.0.0.0/19 is subnetted, 1 subnets
O E2
69.51.160.0 [110/1] via 192.5.40.54, 6d21h, Port-channel61
O E2 199.233.104.0/24 [110/1] via 192.5.40.54, 3w4d, Port-channel61
192.5.40.0/24 is variably subnetted, 19 subnets, 4 masks
D
192.5.40.238/32 [90/131328] via 192.31.0.13, 2d16h, Vlan4094
[90/131328] via 192.31.0.113, 2d16h, Vlan4084
O IA
192.5.40.225/32 [110/2] via 192.5.40.54, 3w4d, Port-channel61
O IA
192.5.40.227/32 [110/4] via 192.5.40.54, 3w4d, Port-channel61
C
192.5.40.240/28 is directly connected, Vlan898
D
192.5.40.168/29 [90/3072] via 192.31.0.113, 7w0d, Vlan4084
[90/3072] via 192.31.0.13, 7w0d, Vlan4094
Snip……
Agenda
•Introduction to Dynamic Routing
•Choosing the Right Protocol
•Configuring Dynamic Routing
•How the ITaP Production Data Network uses
dynamic routing
Choosing the Right Protocol
•Interior Routing Protocols
•Used within an autonomous system
•Used within an area of administrative
control
•Exterior Routing Protocols
•Used between autonomous systems
•Used to peer with networks in which you
have no administrative control
Choosing the Right Protocol
•Interior Routing Protocols
•Static
•RIP
•OSPF
•EIGRP
•ISIS
•Exterior Routing Protocols
•BGP
NOTE: This is not an exhaustive list of protocols available but merely a list of those commonly used.
Choosing the Right Protocol
•Static Routing
•May be suitable on small networks
•Administration intensive as changes have to
be made on each router
•Commonly used for default routing
•0.0.0.0/0  Next Hop Router
Choosing the Right Protocol
•Dynamic Routing Protocol Types
•Distance Vector
•Routing Information Protocol(RIP)
•Interior Gateway Routing Protocol(IGRP)
•Enhanced Interior Gateway Routing
Protocol(EIGRP)
•Link State
•Open Shortest Path First(OSPF)
•Intermediate System to Intermediate
System(ISIS)
•Path Vector
•Border Gateway Protocol(BGP)
Choosing the Right Protocol
•Routing Information Protocol(RIP)
•RFC 1058(RIPv1), 1988
•Classful, no support for VLSM
•No support for authentication
•RFC 2453(RIPv2), 1998
•Classless, support for CIDR
•Support for authentication
•Uses hop count as routing metric
•Slow to converge
•Not very scalable
•Limited to 15 hops
Choosing the Right Protocol
•Interior Gateway Routing Protocol(IGRP)
•Invented by Cisco to overcome limitations of
RIP
•Allows for hop count up to 255
•Allows for multiple route metrics
•Bandwidth
•Delay
•Load
•MTU
•Reliability
•Classful, no support for VLSM
Choosing the Right Protocol
•Enhanced Interior Gateway Routing
Protocol(EIGRP)
•Replaced IGRP
•Maintains a Topology table
•Successors, feasible successors
•Allows for multiple route metrics
•Classless, support for CIDR
•Very fast to converge
•Maintains neighbor relationships
•Diffusing Update Algorithm(DUAL)
•Not as CPU intensive as OSPF
Choosing the Right Protocol
•Open Shortest Path First(OSPF)
•RFC 2328(OSPFv2), 1998
•Maintains neighbor relationships
•Concept of Areas
•Different areas can be used to control
flooding of routing information
•Classless, supports VLSM
•Fast to converge
•CPU Intensive Dijkstra Algorithm
•Designing can be complicated
Choosing the Right Protocol
•Intermediate System to Intermediate
System(ISIS)
•RFC 1142, 1990
•Dijkstra Algorithm
•Mainly used by large service providers
•Does not use IP to carry routing information
•Uses ISO addresses
•Level Concept
•Level 1 or Intra Area
•Level 2 or Inter Area
•Level 1/2 or Both
•Classless, supports VLSM
Choosing the Right Protocol
•Border Gateway Protocol(BGP)
•RFC 4271(BGPv4), 2006
•Peers manually defined
•Used typically for multi-homing to ISP(s)
•Very scalable
•Makes decisions based upon AS Path
•Lots of policy options
•Very granular control
Agenda
•Introduction to Dynamic Routing
•Choosing the Right Protocol
•Configuring Dynamic Routing
•How the ITaP Production Data Network uses
dynamic routing
Configuring Dynamic Routing
•How to configure dynamic routing?
•Choose a protocol that meets your needs
•Each vendor has specific commands but
should have a configuration guide available to
assist
•Plan well to ensure a functional network
•Create a diagram
•Consider high availability technologies
•HSRP
•VRRP
Configuring Dynamic Routing
•Best Practices
•Only enable a routing protocol for interfaces
you intend on using
•If compromised can cause a lot of
problems
•Enable authentication(if available)
•Use authentication to ensure that the
remote routers are valid peers
Configuring Dynamic Routing
•Best Practices Cont…
•Control Network Advertisements
•Only allow networks to be advertised that
should be
•Private Address Space
•Use only within your organization
•Private AS Numbers
•Strip before sending to ISP
Agenda
•Introduction to Dynamic Routing
•Choosing the Right Protocol
•Configuring Dynamic Routing
•How the ITaP Production Data Network uses
dynamic routing
How the ITaP Production Network
Uses Dynamic Routing
•Routing Protocols Used
•Interior
•EIGRP
•OSPF
•Static
•Exterior
•BGP
How the ITaP Production Network
Uses Dynamic Routing
Whiteboard Drawing
Questions?