1 TCP/IP Internetworking (Part 2) (February 9, 2015) © Abdou Illia – Spring 2015

2 Border Router vs. Internal Router Corporate network x.x Border routers connect different networks In this case network x.x and network 60.x.x.x). An “x” indicates anything

3 Border Router vs. Internal Router (cont.) Internal routers connect different subnets in a network In this case, subnets: x, x, and x. Corporate network x.x

4 IP Routing Routing Matches Host Because of multiple alternative routes in router meshes, routers may have several rows that match an IP address. Routers must find All matches and then select the BEST ONE. This is slow and therefore expensive compared to switching. Router A

5 IP Routing (cont.) The Routing Table Each router has a routing table that it uses to make routing decisions Routing Table Rows Each row represents a route for a RANGE of IP addresses—often a network or subnet All packets with destination addresses in this range are routed according to that row Route IP Address Range Governed by the route Metric Next-Hop Router x.x9B

6 The Routing Table Routing Table Columns Row (route) number: Not in real routing tables IP address range governed by the row Metric for the quality of the route (cost, speed, etc.) Next-hop router that should get the packet next if the row is selected as the best match RouteIP Address Range MetricNext-Hop Router x.x9B x.x2B IP Routing (cont.)

7 A Routing Decision The router looks at the destination IP address in an arriving packet (in this case, ). 1. The router determines which rows match (have an IP address range containing the packet’s destination IP address) The router must check ALL rows for possible matches RouteIP Address Range MetricNext-Hop Router x.x9B x.x2B Arriving Packet Match No Match IP Routing (cont.) x8CMatch

8 A Routing Decision 2. After finding all matches, the router then determines the BEST MATCH row 2A. Selects the row with the LONGEST MATCH  60.3.x.x has 16 bits of match  x has 24 bits of match so is a better match 2B. If two or more rows tie for the longest match, router uses the METRIC column value  If cost, lowest metric value is best  If speed, highest metric value is best  Etc. IP Routing (cont.)

9 A Routing Decision 3. After selecting the best-match row, the router sends the packet on to the next-hop router indicated in the best-match row—Next- Hop Router C in this example. RouteIP Address Range MetricNext-Hop Router x.x9B x.x2B Send Packet out to NHR B IP Routing (cont.) x8CBest-Match Row

10 Vertical Communication on Routers Port 1 DL Port 2 DL Port 3 DL Port 4 DL PHY Internet Layer Process Packet Frame Router 1 A Decapsulation Notes: A.Router R1 receives frame in Port 1. Port 1 Data Link decapsulates the IP packet. Port 1 Data Link passes packet to internet Layer.

11 Vertical Communication on Routers Port 1 DL Port 2 DL Port 3 DL Port 4 DL PHY Internet Layer Process Packet Frame Router 1 Router 2 B Encapsulation B.Internet layer sends packet out on Port 4. Data Link process on Port 4 encapsulates packet in a DL frame. Data Link process passes frame to Port 4 PHY.

12 Summary Questions (Part 1) How many layers are there in a router? Can a router be a software program? Suppose that Computer 1 sends a message to Computer 2. Assume that there are two routers (R1 and R2) along the route that leads to Computer 2. Assume that a frame from the message is received by R1 in Port 2. Which of the following will happen next? a) The Data Link layer process in Port 1 will de-encapsulate the IP packet from the frame b) The Physical layer will pass the frame to the Data Link layer process in Port 2 c) The Data Link layer process in Port 2 will de-encapsulate the IP packet from the frame d) None of the above

13 IP Addresses Network Browser Packet Router Packet Route Webserver Software User PC (Host) IP Address= Webserver (Host) IP Address= Host name=eiu.edu

14 IP Address IP is a connectionless protocol IP address is like postal addresses Postal addresses are hierarchical: state, city, postal zone, street, house address IP Addresses have the following hierarchy Network number (tells what network the host is on) Subnet number (tells what segment of network the host is on) Computer number (identifies a particular computer on the segment) Routers look at network part (and segment part for some) to make routing decisions Final router looks at Host part

15 Hierarchical IP Address Network Part (not always 16 bits) Subnet Part (not always 8 bits) Host Part (not always 8 bits) Total always is 32 bits Host School of Business Subnet ( 130 ) EIU Network (139.67) The Internet 13

16 IP Address notations IP addresses Are really strings of 32 bits (1s and 0s) Example: Usually represented by four number segments separated by dots: dotted decimal notation Example:

17 IP Address structure Each IP Address has two main parts: Each Organization is given the Network Part by an IP address Registrar (see For Eastern Illinois University, this is All IP Addresses for Eastern’s computers begin with that Network Part IP Address Network PartLocal Part American Registry for Internet Numbers Check EIU’s IP registration info

18 IP Address structure Network Parts is 8 to 24 bits long For Eastern, it is 16 bits long 16 bits is only an example Local Part Total address is 32 bits, so if the network part is 8 bits, the local part is 24 bits Network Part (8 to 24 bits)

19 Assigning Parts Most Organizations have multiple segments within the organizational network So, usually Local Part is broken in two parts a Segment Part to represent each segment Remaining Bits are the Host Part, designating a particular computer on that segment Network PartSegment Part IP Address (32 bits total) Host Part Local Part

20 Network classes Class A Class B Class C 0.x.x.x to 127.x.x.x x.x to x.x x to x ClassAddress range 0xxx 10xx 110x Leftmost bits 8 bits 16 bits 24 bits Network Part Length Classful IP Addressing Classless IP Addressing (since 1993) Most networks too big for "class C“. Therefore received a "class B" set of addresses instead. With the rapid growth of the Internet, there is a shortage of class B addresses Classful IP addressing is replaced by Classless IP addressing e.g., instead of a full class B, business gets "a set of /16 addresses" # of networks # of host/ network Question: Determine the number of maximum networks and hosts for each class.

21 IP Address Spoofing Trusted Server Victim Server Trust Relationship From: To: Spoofed Source IP Address is used. Attacker’s Client PC Reasons for IP spoofing: Anonymity Exploiting trust relationship IP address spoofing is sending a message with a false IP address with the intent to mislead the receiving device and gain access