1. CIT 384: Network Administration
Routing
CIT 384: Network Administration

2. CIT 384: Network Administration
Topics
Connected Routes
Static Routes
Routing Protocols
RIP
CIT 384: Network Administration

3. CIT 384: Network Administration
Sample routing infrastructure: 3 routers, 3 LANs with PCs, 3 LANs between routers, 3 interfaces/router
CIT 384: Network Administration

4. CIT 384: Network Administration
Routes
Sources of routes
Connected routes
Static routes
Routing protocols
Router will use best match route.
Matching route with longest prefix length.
CIT 384: Network Administration

5. CIT 384: Network Administration
Connected Routes
Routes to networks where rtr has interface.
Router determines these routes from interface IP address and subnet.
Listed in route table with a C prefix.
How to deliver packets to non-connected nets?
Needs routes for those subnets, or
A default route for all other networks.
CIT 384: Network Administration

6. CIT 384: Network Administration
show ip route
Router-251>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
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 to network
/8 is variably subnetted, 2 subnets, 2 masks
C /24 is directly connected, FastEthernet0/0
C /16 is directly connected, FastEthernet0/1
S* /0 [1/0] via
CIT 384: Network Administration

7. CIT 384: Network Administration
show ip route address
Router-251>show ip route
Routing entry for /24
Known via "connected", distance 0, metric 0 (connected, via interface)
Routing Descriptor Blocks:
* directly connected, via FastEthernet0/0
Route metric is 0, traffic share count is 1
Router-251>show ip route
% Network not in table
CIT 384: Network Administration

8. CIT 384: Network Administration
Static Routes
Routes entered by network administrator.
Listed in route table with S prefix.
Easy to understand network behavior.
Avoids problems with routing protocols.
Requires extensive planning for large networks.
Does not adapt to changing networks.
Does not scale to large networks.
CIT 384: Network Administration

9. Creating a Static Route
ip route network subnet destination
ip route
ip route
ip route fa0/1
CIT 384: Network Administration

10. How to configure branch office router R1?
Configure hundreds of static routes on R1, all of which will have S0/1 as destination.
Enable a routing protocol to learn routes.
Add a default route to R1 with outgoing interface S0/1.
CIT 384: Network Administration

11. CIT 384: Network Administration
Default Routes
What happens if no route matches an IP?
Packet is discarded by router.
Unless there is a default route.
Default route matches all destination addrs.
Listed with S* prefix in routing table.
Configuring a default route
ip route
CIT 384: Network Administration

12. CIT 384: Network Administration
Routing Protocols
Routing protocols allow routers to learn.
Routers start knowing only connected routes.
Routers advertise routes to other routers.
Connected routes.
Learned routes from other router’s advertisements.
Routing protocol must avoid loops.
Routers must choose best route when presented with multiple routes for the same subnet.
CIT 384: Network Administration

13. CIT 384: Network Administration

14. CIT 384: Network Administration
Interior and Exterior
Interior Gateway Protocols (IGPs)
Used inside a single autonomous system.
Examples:
RIP
IGRP
OSPF
Exterior Gateway Protocols (EGPs)
Used between different autonomous systems.
Identify with autonomous system numbers (ASN)
Border Gateway Protocol (BGP)
CIT 384: Network Administration

15. CIT 384: Network Administration
Usage of IGPs and EGPs
CIT 384: Network Administration

16. Routing Protocol Algorithms
Distance vector: counts number of routers (hops) between a router and destination subnet.
Link state: sum of interface cost settings for all links in route, defaulting to interface bandwidth.
Algorithm Type
IGPs
Distance vector
RIPv1, RIPv2, IGRP
Link state
OSPF
Balanced hybrid
EIGRP
CIT 384: Network Administration

17. CIT 384: Network Administration
Comparing RIP and EIGRP costs, as RIP only uses hop count, while EIGRP considers bandwidth as well.
CIT 384: Network Administration

18. CIT 384: Network Administration
Summarization
Routers perform better with fewer routes.
Summarization reduces # of routes.
Manual summarization allows network admin to control summary routes.
Autosummarization allows router to automatically create summary routes for adjacent networks.
CIT 384: Network Administration

19. CIT 384: Network Administration
Convergence
Convergence is the process by which routers collectively realize network has changed, advertise information about changes to other routers, and all routers choose the current best routes for each network. Occurs when:
A link goes down.
A link bcomes available.
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20. CIT 384: Network Administration
Other Differences
How are routing updates sent?
Broadcast (RIPv1)
Multicast
Authentication
Prevents routing update spoofing.
Attackers could change routes to:
Sniff packets from networks they don’t have a machine located on.
Launch DoS attacks against routing infrastructure.
CIT 384: Network Administration

21. CIT 384: Network Administration
IGP Comparison
Feature
RIPv1
RIPv2
EIGRP
OSPF
Classless n y
VLSM support
Sends subnet mask in update
Distance vector
Link state
Autosummarization support
Manual summarization support
Proprietary
Uses multicast for updates
Authentication support
Convergence
Slow
Fast
CIT 384: Network Administration

22. Administrative Distance
Metrics aren’t comparable between IGPs.
RIP values are small hop counts.
EIGRP values involve large bandwidth numbers.
Use AD values to determine which to use.
Low AD values indicate better routes.
Connected, then static are the best.
CIT 384: Network Administration

23. Default Administrative Distances
Route Type
Administrative Distance
Connected
Static 1
BGP (external routes) 20
EIGRP (internal routes) 90
IGRP
100
OSPF
110
IS-IS
115
RIP
120
EIGRP (external routes)
170
BGP (internal routes)
200
Unusable
255
CIT 384: Network Administration

24. CIT 384: Network Administration
Configuring RIP
R1# configure terminal
R1(config)# router rip
R1(config-router)# version 2
R1(config-router)# network
R1(config-router)# network
R1(config-router)# network
CIT 384: Network Administration

25. CIT 384: Network Administration
show ip route (RIP)
Albuquerque#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
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 not set
/24 is subnetted, 6 subnets
R [120/1] via , 00:00:16, Serial0/1/0
R [120/1] via , 00:00:09, Serial0/0/1
C is directly connected, FastEthernet0/0
C is directly connected, Serial0/1/0
CIT 384: Network Administration

26. CIT 384: Network Administration
show ip protocols
Albuquerque#show ip protocols
Routing Protocol is "rip"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set !
! The next line identifies the time interval for periodic routing updates, and when this
! router will send its next update.
Sending updates every 30 seconds, next due in 22 seconds
Invalid after 180 seconds, hold down 180, flushed after 240
Redistributing: rip
! The next few lines result from the version 2 command being configured
Default version control: send version 2, receive version 2
Interface Send Recv Triggered RIP Key-chain
FastEthernet0/
Serial0/0/
Serial0/1/
Automatic network summarization is in effect
Maximum path: 4
CIT 384: Network Administration

27. CIT 384: Network Administration
show ip protocols !
! The next two lines reflect the fact that this router has a single network command,
! namely network If other network commands were configured, these networks
! would also be listed.
Routing for Networks:
! The next section lists the IP addresses of neighboring routers from which Albuquerque
! has received routing updates, and the time since this router last heard from the
! neighbors. Note is Seville, and is Yosemite.
Routing Information Sources:
Gateway Distance Last Update
:00:25
:00:20
Distance: (default is 120)
CIT 384: Network Administration

28. CIT 384: Network Administration
RIP Messages
Albuquerque#debug ip rip
RIP protocol debugging is on
Albuquerque#
! Update sent by Albuquerque out Fa0/0:
! The next two messages tell you that the local router is sending a version 2 update
! on Fa0/0, to the multicast IP address. Following that, 5 lines list the
! 5 subnets listed in the advertisement.
*Jun 9 14:35:08.855: RIP: sending v2 update to via FastEthernet0/0 ( )
*Jun 9 14:35:08.855: RIP: build update entries
*Jun 9 14:35:08.855: /24 via , metric 2, tag 0
*Jun 9 14:35:08.855: /24 via , metric 2, tag 0
*Jun 9 14:35:08.855: /24 via , metric 1, tag 0
*Jun 9 14:35:08.855: /24 via , metric 2, tag 0
*Jun 9 14:35:08.855: /24 via , metric 1, tag 0
CIT 384: Network Administration

29. CIT 384: Network Administration
RIP Messages
! The next 4 messages are about a RIP version 2 (v2) update received by Albuquerque
! from Seville (S0/1/0), listing three subnets. Note the mask is listed as /24.
*Jun 9 14:35:13.819: RIP: received v2 update from on Serial0/1/0
*Jun 9 14:35:13.819: /24 via in 2 hops
*Jun 9 14:35:13.819: /24 via in 1 hops
*Jun 9 14:35:13.819: /24 via in 1 hops
! from Yosemite (S0/0/1), listing three subnets. Note the mask is listed as /24.
*Jun 9 14:35:16.911: RIP: received v2 update from on Serial0/0/1
*Jun 9 14:35:16.915: /24 via in 1 hops
*Jun 9 14:35:16.915: /24 via in 2 hops
*Jun 9 14:35:16.915: /24 via in 1 hops
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30. CIT 384: Network Administration
References
James Boney, Cisco IOS in a Nutshell, 2nd edition, O’Reilly, 2005.
Cisco, Cisco Connection Documentation,
Cisco, Internetworking Basics,
Wendell Odom, CCNA Official Exam Certification Library, 3rd edition, Cisco Press, 2007.
CIT 384: Network Administration