Exercise 1 INTERNET. x.x.x.254. net /24. net /24. x.x.x.33. x.x.x.254. x.x.x.52. x.x.x.254. x.x.x.254. x.x.x.

Transcription

1 Exercise 1 Given the IP network below: Assign feasible IP addresses to the interfaces and write down a feasible routing table for routers A and B guaranteeing full connectivity x.x.x.33 x.x.x.254 net /24 B x.x.x.254 Net /24 x.x.x.254 A Net /24 x.x.x.52 x.x.x.254 INTERNET net /24 Net /24 x.x.x.254

2 Solution 1 A Routing Table network netmask first hop B Routing Table network netmask first hop A Interfaces interface address netmask A B C B Interfaces interface address netmask A B C network netmask first hop

3 Routing & Forwarding

4 Activity 1 Given the network below: Router eth0 A D eth1 B Let IP-x and MAC-x be the IP and Ethernet Addresses of x=[a,b,c,d] respectively. C

5 Activity 1 Router eth0 A D eth1 B We assume empty ARP tables for A, D and the Router Host A needs to send out an IP packet destined to host D. Upon reception, host D answers with a packet destined to A. a) Plot the sequence of all messages/packets exchanged among the three entities with the correspondent addresses used (at both the IP and Ethernet level) C

6 Solution 1 Router A D ARP request src: MAC-A dest: broadcast layer ARP: IP-A, MAC-A, IP-B,? B C ARP reply src: MAC-B dest: MAC-A layer ARP: IP-A, MAC-A, IP-B, MAC-B

7 Solution 1 Router A D PACKET A-D src: MAC-A dest: MAC-B layer 3: src: IP-A dest: IP-D B C

8 Solution 1 Router A D B C ARP request src: MAC-C dest: broadcast layer ARP: IP-C, MAC-C, IP-D,? ARP reply src: MAC-D dest: MAC-C layer ARP: IP-C, MAC-C, IP-D, MAC-D

9 Solution 1 Router A D B C PACKET A-D src: MAC-C dest: MAC-D layer 3: src: IP-A dest: IP-D PACKET D-A src: MAC-B dest: MAC-A layer 3: src: IP-D dest: IP-A PACKET D-A src: MAC-D dest: MAC-C layer 3: src: IP-D dest: IP-A

10 Activity 2 Bridge eth0 A D eth1 B b) Solve the same exercise, assuming now the interconnecting device is a Bridge C

11 Solution 2 Bridge A D B C ARP request src: MAC-A dest: broadcast layer ARP: IP-A, MAC-A, IP-D,? ARP reply src: MAC-D dest: MAC-A layer ARP: IP-A, MAC-A, IP-D, MAC-D

12 Solution 2 Bridge A D PACKET A-D src: MAC-A dest: MAC-D layer 3: src: IP-A dest: IP-D B C PACKET D-A src: MAC-D dest: MAC-A layer 3: src: IP-D dest: IP-A

13 Activity 3 A router has the following routing table and the following interfaces network netm ask first hop interface eth0 IP address netm ask interface eth1 IP address netm ask interface eth2 IP address netm ask How does the router forward the IP packets with the following IP destination addresses?

14 Solution 3 network netm ask first hop interface eth0 IP address netm ask interface eth1 IP address netm ask interface eth2 IP address netm ask Directly Forwarded through interface eth Forwarded to the next hop Forwarded to the default gateway

15 Ex. 4 A router has the following routing table and interfaces configuration. eth eth Network Netmask Next Hop The router receives packets with the following IP destination addresses: received from interface eth received from interface eth0 Specify the behavior of the router for each packet. What kind of forwarding is implemented (direct, indirect)? Which is thenext hop Which the line of the routing table used to decide the next hop?

16 20/09/2006 -Ex AND 1. /20 = /19 = /16 = /19 = /0 = OK OK OK Network Netmask Next Hop Indirect Forwarding

17 20/09/2006 -Ex AND 1. /20 = /19 = /16 = /19 = /0 = OK OK OK OK Network Netmask Next Hop Indirect Forwarding

18 20/09/2006 -Ex AND 1. /20 No match 2. /19 No match 3. /16 No match 4. /19 No match 5. /0 = OK Network Netmask Next Hop Indirect Forwarding

19 20/09/2006 -Ex. 4 eth eth Network Netmask Next Hop Limited broadcast, router drops the packet from eth1 Direct broadcast to subnet , router forwards the packet through eth from eth0 It is never a valid destination address, the router drops the packet

20 Activity 4 A router has the following routing table and the following interfaces. The router receives 8 packets whose destination IP addresses and incoming interfaces are reported below. Indicate what is the behavior of the router for each packet indicating: If the packet is forwarded or not In the case the packet is forwarded, the next hop (IP address) whether the forwarding is direct or indirect eth0 Interface IP Address Netmask Eth R eth2 Eth1 Eth eth1 Network Netmask Next Hop RECEIVED PACKETS A from eth2 B from eth0 C from eth2 D from eth1 E from eth1 F from eth1 G from eth0 H from eth1

21 Solution 4 eth0 Interface IP Address Netmask Eth R eth2 Eth1 Eth eth1 Network Netmask Next Hop A from eth2 direct forwarding through eth0 B direct broadcast address: not forwarded C direct forwarding through eth1

22 R Solution 4 eth0 eth1 Interface Eth eth2 Eth D from eth1 Indirect forwarding, 1st line routing table, NH: E from eth1 Indirect forwarding, 4th line routing table, NH: F from eth1 Indirect forwarding, 3rd line routing table, NH: Eth0 Network IP Address Netmask Netmask Next Hop

23 Solution 4 R eth0 eth1 Interface Eth eth2 Eth Eth0 Network IP Address Netmask Netmask Next Hop G from eth0 Indirect forwarding, last line routing table, NH: H from eth1 special address, only source, not processed