Static Routing Design Exercises

Transcription

1 Static Routing Design Exercises Mario Baldi Flavio Marinone Fulvio Risso Static_routing_ex - 1 Copyright notice: page 2

2 Copyright notice This set of transparencies, hereinafter referred to as slides, is protected by copyright laws and provisions of International Treaties. The title and copyright regarding the slides (including, but not limited to, each and every image, photography, animation, video, audio, music and text) are property of the authors specified on page 1. The slides may be reproduced and used freely by research institutes, schools and Universities for non-profit institutional purposes. In such cases, no authorization is requested. Any total or partial use or reproduction (including, but not limited to, reproduction on magnetic media, computer networks, and printed reproduction) is forbidden, unless explicitly authorized by the authors by means of written license. Information included in these slides is deemed as accurate at the date of publication. Such information is supplied for merely educational purposes and may not be used in designing systems, products, networks, etc. In any case, these slides are subject to changes without any previous notice. The authors do not assume any responsibility for the contents of these slides (including, but not limited to, accuracy, completeness, enforceability, updated-ness of information hereinafter provided). In any case, accordance with information hereinafter included must not be declared. In any case, this copyright notice must never be removed and must be reported even in partial uses. Static_routing_ex - 2 Copyright notice: page 2

3 Routing Table n Used by routers to decide how to forward each packet n Each row contains two columns: n (1) Destination (a prefix) n (2) Next hop (an IP address) n E.g.,: from here, to reach Naples, go to Rome n Additional information: cost n Used to choose among multiple next hops to the same destination n Backup/fault tolerance, load balancing Static_routing_ex - 3 Copyright notice: page 2

4 Designing Static Routing n Identify the best path from each router to each destination n A routing tree for each network node n Root: node being considered n Leaves: all possible destinations n Logical IP subnets n Branches (edges): show the path taken by packets n Minimizes a cost function n Number of hops, delay, link load, link bandwidth n Assign cost/weight to each link n Ensure consistency for different nodes!! n Extract routing table entries for each router n For each router, identify next hop to each destination Static_routing_ex - 4 Copyright notice: page 2

5 Static_routing_ex - 5 Copyright notice: page 2 Identify the best path to a destination n Node dependent n Routing trees for F and H A B E C D G H F A B E C D G H F A B E C D G H F

6 Next Hop n A neighbor router n The address entered in the routing table must be directly connected n Routers do not have visibility on the whole path n Their horizon towards each destination is limited oto the next hop A F B E D G C H Static_routing_ex - 6 Copyright notice: page 2

7 Routing Table Router F example Destination A B C D E G H Next-hop E E H H E H H A F B E D G C H Static_routing_ex - 7 Copyright notice: page 2

8 Routing n Asymmetrical Route n Packets from A to B travel on a different path than packets form B to A n Not unusual in IP networks n Each source has its own tree n Usually table contains a default route n Next hop to be used for any unspecified destination n In peripheral areas n the rest of the world is in the same direction n Usually a sequence of default routers leads to a router that has knowledge of specific routes n Next hop ó Gateway ó Router Static_routing_ex - 8 Copyright notice: page 2

9 Routing Algorithm on a Router Pick an interface PKT Direct routing Forwarding Is destination in the LIS of the interface? Y Activate data-link mechanisms for delivery N Y Are there more interfaces? N Select next hop router Longest Prefix Matching in the routing table Send packet Static_routing_ex - 9 Copyright notice: page 2

10 Routing Table Content n Direct routing information n Interface configuration n Next-hop is often shown as the IP address of the router on the interface n Cost, if present, is minimum n Static Routes n Manually configured by network administrator n Must know network topology n Be aware of reachability n Must compute best route n Dynamic Routing n Routing protocol to discover network topology n Routing algorithm to build routing tree n Ensuring consistency Static_routing_ex - 10 Copyright notice: page 2

11 Routing Table Content 1. Remote destinations (Local Destinations) 4. Aggregatable networks / /24 2. Best path.1 3. Next Hop Routing table: (static routes) S / S / S / S / (direct routes) D / D / D / / / / / / / /24 Static_routing_ex - 11 Copyright notice: page 2

12 Filling Out a Routing Table Routing table S S S S S D D D S / / /21 9.0/ / / / / / / /24 Static_routing_ex - 15 Copyright notice: page 2

13 Network Administration Exercise n Address assignment n Link cost assignment and tree computation n Next hop identification and routing table R1 2.2/25 Ethernet0 LAN Hosts 3.10/30 Serial0 Net 3 Ethernet0 Serial0 Serial0 2.1/25 3.1/30 3.2/30 Prefixes x.y 3.9/30 Serial0 R2 Net 4 0.1/23 Ethernet0 Serial1 3.5/30 3.6/30 Serial1 LAN Hosts LAN 2 63 Hosts R3 Net 5 R4 Ethernet /25 Static_routing_ex - 16 Copyright notice: page 2

14 R4 Routing Tree R1 Net 3 R2 LAN 1 LAN 0 LAN 2 Net 4 R3 Net 5 R4 Static_routing_ex - 17 Copyright notice: page 2

15 / /28 Static Routing Exercise R AO.2.100/ /24 R TO.2.88/ /27 Internet / R MI / /28 R MV /24 R GE /25 R VC R IM R SV / / /29 Static_routing_ex - 19 Copyright notice: page 2

16 / /28 Link Costs R AO /24 R TO.89 Cost: /27 Internet / R MI / /28 R MV /24 R GE /25 R VC R IM R SV / / /29 Static_routing_ex - 20 Copyright notice: page 2

17 Reachable Networks: End Destinations n /24 n /25 n /26 n /27 n /27 n /27 n /28 n /28 n /28 n /29 Static_routing_ex - 21 Copyright notice: page 2

18 Reachable Networks: Routers n /30 n /30 n /30 n /30 n /30 n /30 n /30 n /30 n /30 Static_routing_ex - 22 Copyright notice: page 2

19 Solution n Router R MI n Directly connected networks n /30 n /30 n Internet connection: /30 assigned by Internet Service Provider n Router will automatically generate direct entries Type Dest. Net Gateway Metric D / D / D / Static_routing_ex - 23 Copyright notice: page 2

20 Solution n Router R MI n Available next hops n R TO à n R GE à n à Internet n Default route to with Cisco syntax: # ip route n Networks that can be reached through R TO n LAN TO à /24 n LAN VC à /26 n ISDN à /27 n LAN MV1 à /27 Static_routing_ex - 24 Copyright notice: page 2

21 Solution n LAN AO1 à /27 n LAN MV2 à /28 n LAN AO2 à /28 n P-P TO-GE à /30 n P-P TO-AO à /30 n P-P TO-MV à /30 n P-P TO-VC à /30 n Networks reachable through R GE n LAN GE à /25 n LAN IM à /28 n LAN SV à /29 n P-P GE-IM à /30 n P-P GE-SV à /30 n P-P GE-FORN à /30 n Other network à /24 Static_routing_ex - 25 Copyright notice: page 2

22 Solution n One entry must be created in the routing table for each reachable network n With Cisco syntax: # ip route # ip route # ip route Static_routing_ex - 26 Copyright notice: page 2

23 Solution: R MI routing table Type Destination Net Gateway Metric S / S / S / S / S / S / S / S / S / S / S / S / S / S / S / S / S / S / S / Static_routing_ex - 27 Copyright notice: page 2

24 Solution n 19 routes n We should try to aggregate routes that use the same next hop n Shorter prefix including multiple longer ones n Level of aggregation depends on the addressing plan n The routing table shown by the router will also show direct routes Static_routing_ex - 28 Copyright notice: page 2

25 Aggregating in R MI Routing Table /25 /26 /28 Type Destination Net Gateway Metric S / S / S / S / S / S / S / S / S / S / S / S / Static_routing_ex - 29 Copyright notice: page 2

26 Aggregating in R MI Routing Table /29 Type Destination Net Gateway Metric S / S / S / S / S / S / S / If we knew for sure that /30 is not reachable through the default route or that a specific route will be introduced for it if neeed, we could further aggregate in /28 Static_routing_ex - 30 Copyright notice: page 2

27 R MI Routing Table with Aggregation n 11 routes Type Destination Net Gateway Metric S / S / S / S / S / S / S / S / S / S / S / Static_routing_ex - 31 Copyright notice: page 2

28 R MI Routing Table with Aggregation n With addressing plan designed to enable aggregation: only 4 routes!! Type Destination Net Gateway Metric S / S / S / S / Static_routing_ex - 32 Copyright notice: page 2

29 Other Routers n R TO and R GE routing tables are simpler n More peripheral n A large fraction of destination networks can be reached through the default gateway R TO Cost: 2 R MI R GE Static_routing_ex - 33 Copyright notice: page 2

30 R TO Routing Table n Direct routes Type Destination Net Gateway Metric D / D / D / D / D / D / n Available next hops n R MI à n R GE à n R AO à n R MV à n R VC à Static_routing_ex - 34 Copyright notice: page 2

31 R TO Routing Table n Static routes Type Destination Net Gateway Metric S / S / S / S / S / S / n No aggregation possible: next hops are all different! Static_routing_ex - 35 Copyright notice: page 2

32 R GE Routing Table n Direct routes Type Destination Net Gateway Metric D / D / D / D / D / D / n Available next hops n R MI à n R TO à n R IM à n R SV à n Other network à Static_routing_ex - 36 Copyright notice: page 2

33 R GE Routing Table n Static routes Type Destination Net Gateway Metric S / S / S / S / Static_routing_ex - 37 Copyright notice: page 2