Troubleshooting IP Addressing 1. Open a DOS window and ping 127.0.0.1 This is the diagnostic or loopback address If successful, IP stack is then considered to be initialized If it fails, then you have an IP stack failure and need to reinstall TCP/IP on the host 2. From the DOS window, ping the IP address of the local host If that’s successful, then your Network Interface Card (NIC) card is functioning If it fails, then there is a problem with the NIC card

Troubleshooting IP Addressing 3. From the DOS window, ping the default gateway (router) If the ping works, it means that the NIC is plugged into the network and can communicate on the local network If it fails, then you have a local physical network problem that could be happening anywhere from the NIC to the router 4. If steps 1 through 3 were successful, try to ping the remote server If that works, then you know that you have IP communication between the local host and the remote server also that the remote physical network is working

Determining IP Address Problems It’s common for a host, router, or other network device to be configured with the wrong IP address, subnet mask, or default gateway First step is to draw the whole network and IP addressing scheme For example take a look on the following case

Determining IP Address Problems A user in the Sales department calls and tells you that he can’t get to ServerA in the Marketing department You ask him if he can get to ServerB in the Marketing department, but he doesn’t know because he doesn’t have rights to log on to that server. What do you do?

Determining IP Address Problems You ask the client to go through the four troubleshooting steps that we learned Steps 1 through 3 work, but step 4 fails By looking at the figure, can you determine the problem? First, the WAN link between the Lab_A router and the Lab_B router shows the mask as a /27 You should already know this mask is 255.255.255.224 and then determine that all networks are using this mask

Determining IP Address Problems The network address is 192.168.1.0. What are our valid subnets and hosts? 256 – 224 = 32 So this makes our subnets 32, 64, 96, 128, etc So, by looking at the figure, you can see that subnet 32 is being used by the Sales department, the WAN link is using subnet 96, and the Marketing department is using subnet 64

Determining IP Address Problems Now you’ve got to determine what the valid host ranges are for each subnet The valid hosts for the Sales LAN are 33 through 62—the broadcast address is 63 because the next subnet is 64, right? For the Marketing LAN, the valid hosts are 65 through 94 (broadcast 95), and for the WAN link, 97 through 126 (broadcast 127) By looking at the figure, you can determine that the default gateway on the Lab_B router is incorrect That address is the broadcast address of the 64 subnet so there’s no way it could be a valid host

Optimization & Troubleshooting IPCONFIG Entered fro the command prompt and it displays the IP address information for the local host PING One of the most commonly used tool for troubleshooting the TCP/IP problems ROUTE Displays the local routing table TRACERT Informs about the health of the route Shows the hops, and how long it took to get from one router to another

Optimization & Troubleshooting NETSTAT Displays the TCP/IP protocol statistics NBTSTAT Displays the current NETBIOS name cache Event viewer Windows based tool. Whenever TCP/IP has a problem initializing, an error message displays and an entry is logged in the system event log.

Routing Basics The term routing is used for taking a packet from one device and sending it through the network to another device on a different network Routers don’t really care about hosts—they only care about networks and the best path to each network The logical network address of the destination host is used to get packets to a network through a routed network Then the hardware address of the host is used to deliver the packet from a router to the correct destination host

Routing Basics To be able to route packets, a router must know, at a minimum, the following: Destination address Neighbor routers from which it can learn about remote networks Possible routes to all remote networks The best route to each remote network How to maintain and verify routing information

Routing Basics The router learns about remote networks from neighbor routers or from an administrator The router then builds a routing table that describes how to find the remote networks If a network is directly connected, then the router already knows how to get to it If a network isn’t connected, the router must learn how to get to the remote network in two ways: by using static routing, meaning that someone must hand-type all network locations into the routing table or through something called dynamic routing

Routing Basics In dynamic routing , a protocol on one router communicates with the same protocol running on neighbor routers The routers then update each other about all the networks they know about and place this information into the routing table If a change occurs in the network, the dynamic routing protocols automatically inform all routers about the event If static routing is used, the administrator is responsible for updating all changes by hand into all routers Typically, in a large network, a combination of both dynamic and static routing is used

The IP Routing Process

The IP Routing Process A router receives the frame and checks the received frame check sequence (FCS); if errors occurred, the frame is discarded. The router makes no attempt to recover the lost packet. If no errors occurred, the router checks the Ethernet Type field for the packet type, and extracts the packet. The Data Link header and trailer can now be discarded. Assuming an IP packet, the router checks its IP routing table for the most specific prefix match of the packet’s destination IP address

The IP Routing Process The matched routing table entry includes the outgoing interface and next-hop router; this information points the router to the adjacency information needed to build a new Data Link frame. Before creating a new frame, the router updates the IP header TTL field, requiring a re-computation of the IP header checksum The router encapsulates the IP packet in a new Data Link header (including the destination address) and trailer (including a new FCS) to create a new frame

Routing Protocol Basics Administrative Distances An administrative distance is an integer from 0 to 255 The administrative distance (AD) is used to rate the trustworthiness of routing information received on a router from a neighbor router 0 is the most trusted and 255 means no traffic will be passed via this route.

Administrative Distance (AD)

Routing Protocol Basics If a router receives two updates listing the same remote network, the first thing the router checks is the AD If one of the advertised routes has a lower AD than the other, then the route with the lowest AD will be placed in the routing table If both advertised routes to the same network have the same AD, then routing protocol metrics (such as hop count or bandwidth of the lines) will be used to find the best path to the remote network The advertised route with the lowest metric will be placed in the routing table.

Routing Protocol Basics If a network is directly connected, the router will always use the interface connected to the network If an administrator configures a static route, the router will believe that route over any other learned routes You can change the administrative distance of static routes, but, by default, they have an AD of 1

Routing Protocols There are three classes of routing protocols: Distance vector Link state Hybrid

Distance vector Protocols The distance-vector protocols find the best path to a remote network by judging distance Each time a packet goes through a router, that’s called a hop The route with the least number of hops to the network is determined to be the best route The vector indicates the direction to the remote network RIP and IGRP are examples of distance-vector routing protocols They send the entire routing table to directly connected neighbors

Link-state Protocols In link-state protocols, also called shortest-path-first protocols, the routers each create three separate tables One of these tables keeps track of directly attached neighbors, one determines the topology of the entire internetwork, and one is used as the routing table Link-state routers know more about the internetwork than any distance-vector routing protocol OSPF is an example of a completely link state IP routing protocol Link state protocols send updates containing the state of their own links to all other routers on the network

Hybrid Protocols Hybrid protocols use aspects of both distance vector and link state EIGRP (Enhanced Interior Gateway Routing Protocol) is an example