Troubleshooting IP and NAT PDF

Network Boundaries and Troubleshooting  Routers as Gateways The router provides a gateway through which hosts on one network can communicate with hosts on different networks. Each interface on a router is connected to a separate network. The IPv4 address assigned to the interface identifies...

Network Boundaries and Troubleshooting  Routers as Gateways The router provides a gateway through which hosts on one network can communicate with hosts on different networks. Each interface on a router is connected to a separate network. The IPv4 address assigned to the interface identifies which local network is connected directly to it. Host PCs typically sets the router as their default gateway  Routers as DHCP Server Dynamic Host Configuration Protocol (DHCP) - network server that automatically provides assigns IP addresses, default gateways and other network parameters to client devices. When a wireless router is configured to be a DHCP server for the local network, it automatically sends the correct interface IPv4 address to the hosts as the default gateway address. Routers as DHCP Server The default IPv4 address configured on the local wireless router interface is usually the first host address on that network. It also provides the subnet mask designated by the network administrator Many ISPs also use DHCP servers to provide IPv4 addresses to the internet side of the wireless router installed at their customer sites. The network assigned to the internet side of the wireless router is referred to as the external, or outside, network. When a wireless router is connected to the ISP, it acts like a DHCP client to receive the correct external network IPv4 address for the internet interface. ISPs usually provide an internet-routable address, which enables hosts connected to the wireless router to have access to the internet. Importance of Routing Router is a networking device that connects multiple Layer 3, IP networks (logical). Switches, which make their forwarding decision based on the Layer 2, MAC address (physical). Fa1/1 0/1 Routing Table Entries Type Network Port Type - The connection type. C stands for directly connected. C 10.0.0.8/8 FastEthernet0/0 Network - The network address. C 172.16.0.0/16 FastEthernet0/1 Port - The interface used to forward packets to the network.  Routing Table Entries Routers must use routing tables to store information: Routing tables are not concerned with the exact addresses of individual hosts but the addresses of networks, and the best path to reach those networks. Entries can be made to the routing table in two ways: dynamically updated by information received from other routers in the network, or manually If the router cannot determine where to forward a message, it will drop it. Network administrators configure a default route that is placed into the routing table so that a packet will not be dropped due to the destination network not being in the routing table. Assessment  Assessment 1. What is the default gateway for H1? 192.168.1.1 2. What is the default gateway for H2? 10.0.0.1 3. What is the default gateway for H3? 172.16.0.50  Network Address Translation The process used to convert private addresses to internet-routable addresses is called Network Address Translation (NAT). With NAT, a private (local) source IPv4 address is translated to a public (global) address. The process is reversed for incoming packets. Pros: Saves Public IPs Flexibility and Network Security Source: OTTVerse Cons: Breaks end-to-end IP traceability. Delays due to translation.  Network Address Translation – Types 1. Static NAT: One-to-One mapping. 2. Dynamic NAT: Pool of public IPs. Source: NetworkAcademy.io Source: NetworkAcademy.io Network Address Translation – Types 3. Port Address Translation– Maps multiple private IP Address and Ports – Apartment Analogy hosts to one public IP by using unique port numbers. Source: Unplash The IP address can be seen as the number of an apartment building Source: NetworkAcademy.io The Port number is your apartment number Network Address Translation – Terms 1. Inside Local: Private IP of a device within the local network. 2. Inside Global: Public IP used to represent the local device on the internet. 3. Outside Local: Public IP address of an external device from the local perspective. 4. Outside Global: Public IP of the external device used on the internet. How NAT Works? – Basic Translation 1. Host 10.1.1.1 sends a packet to an external network. 2. The router translates the private IP (10.1.1.1) to a public IP and logs it in the NAT table. 3. The router forwards the packet with the public IP as the source. 4. The external host sends a response to the public IP. 5. The router translates the public IP back to the private IP (10.1.1.1) and delivers the response.  How NAT Works? – NAT overloading example (PAT) PAT (Port Address Translation) Process 1. Overloading Multiple Hosts: All private hosts share one public IP, with each assigned a unique port number. 2. NAT Table Translation: Private IP → Public IP with unique port numbers. 3. Traffic Routing: Outbound: Router translates IP and assigns a port. Inbound: Router maps the port back to the correct private host. Pros: Cons: Conserves public IPs by allowing If the PAT router fails, all many private IPs to share one public communication using the public IP IP using ports. stops. Assessment Assessment Basics of IP Addressing IP Address: Unique identifier for devices on a network (e.g., 192.168.2.7). Subnet Mask: Divides network and host portions (e.g., 255.255.255.0 or /24). Default Gateway: Routes traffic outside local subnet (192.168.2.3 & 192.168.3.3). Common Issues: Overlapping IPs. Incorrect subnet masks Mismatched gateways. Command – line tools Packet InterNet Groper (ping) – Uses an ICMP echo request and replies to test if a host IP stack is initialized and alive on the network.  Command – line tools Traceroute is a computer network diagnostic tool for displaying the route and measuring transit delays of packets across an Internet Protocol network Windows - tracert MAC/Linux - traceroute  Command – line tools ARP (Address Resolution Protocol) resolves IP addresses to MAC addresses, bridging Layer 3 and Layer 2 to enable devices on a local network to communicate at the Data Link Layer. Command: arp -a – Displays IP–to–MAC-address mappings on a Windows PC. Command – line tools ipconfig /all – Used only from a command prompt. Shows you the PC network configuration. IP Troubleshooting The Four Basic Troubleshooting Steps: 1. Verify IP configuration. 2. Check subnet mask and gateway. 3. Analyze topology. 4. Test communication. Analysis: ISiTE Subnet (192.168.1.64 /27): Range: 192.168.1.65 - 192.168.1.94 Broadcast: 192.168.1.95 Gateway cannot be the broadcast address (192.168.1.95). Therefore, 192.168.1.94 is the correct default gateway for ISiTE  IP Troubleshooting – Analysis 1. Benefits LAN (192.168.1.24/29): Valid Hosts: 192.168.1.25 - 192.168.1.30 Broadcast: 192.168.1.31 Therefore, Configured Correctly 2. WAN Link (192.168.1.40/29): Valid Hosts: 192.168.1.41 - 192.168.1.46 Broadcast: 192.168.1.46 Therefore, Configured Correctly 3. Payroll LAN (192.168.1.80/29): Valid Hosts: 192.168.1.81 - 192.168.1.86 Broadcast: 192.168.1.87 Issue Identified: Payroll2 has been configured with the broadcast address (192.168.1.87), which is invalid for a host.  IP Troubleshooting – Finding valid hosts Subnet for R1 and ACES (192.168.10.64/26): Subnet Mask: /26 or 255.255.255.192 Block Size = 64 (256 - 192). Usable Hosts: 192.168.10.65 - 192.168.10.126 IP: 192.168.10.66 IP: 192.168.10.34 Subnet for R2 and ISITE (192.168.10.32/28): Subnet Mask: 255.255.255.192 Subnet Mask: 255.255.255.240 Subnet Mask: /28 or 255.255.255.240 Block Size = 16 (256 - 240). Usable Host Range: 192.168.10.33 - 192.168.10.46 Checkpoint Question On which of the following devices are you most likely to be able to implement NAT? A. Hub B. Ethernet switch C. Router D. Bridge Checkpoint Question When configuring the IP settings on a computer on one subnet to ensure that it can communicate with a computer on another subnet, which of the following is desirable? A. Configure the computer with the same default gateway as the other computer. B. Configure the computer with the same subnet mask as the other computer. C. Configure the computer with a default gateway that matches the IP address of the interface of the router that is attached to the same subnet as the computer. D. Configure the computer with a subnet mask that matches the IP address of the interface of the router that is attached to the same subnet as the computer Checkpoint Question A network administrator is connecting two hosts directly through their Ethernet interfaces, as shown in the illustration. Ping attempts between the hosts are unsuccessful. What can be done to provide connectivity between the hosts? A. A crossover cable should be used in place of the straight-through cable. B. A rollover cable should be used in place of the straight-through cable. C. A default gateway needs to be set on each host. D. The subnet masks should be set to 255.255.255.0. Checkpoint Question You have one IP address provided from your ISP with a /30 mask. However, you have 300 users that need to access the Internet. What technology will you use to implement a solution? A. PAT B. VPN C. DNS D. LANs