Network+ Chapter 7

Convergence?

Convergence occurs when all routers share a consistent view of the network. Each router will used converged path information to insert next hop information for each learned path into the routing table. It does this by choosing the route with the lowest metric.

What are the 3 routing protocols categories?

Distance vector routing Link State Hybrid

What is EIGRP?

Enhanced Interior Gateway Routing Protocol EIGRP is a hybrid routing protocol developed by Cisco for routing within an AS. • EIGRP uses a composite number for the metric, which indicates bandwidth and delay for a link. The higher the bandwidth, the lower the metric. • EIGRP is a classless protocol. EIGRP is best suited for medium to large private networks.

What is IS-IS?

Intermediate System to Intermediate System IS-IS is a link-state routing protocol used for routing within an AS. • IS-IS uses relative link cost for the metric. • IS-IS is a classless protocol. • The original IS-IS protocol was not used for routing IP packets; use integrated IS-IS to include IP routing support. • IS-IS divides a large network into areas. There is no area 0 requirement, and IS-IS provides greater flexibility for creating and connecting areas than OSPF . • L1 routers share routes within an area. L2 routers share routes between areas. An L1/L2 router can share routes with both L1 and L2 routers. • A network link is the boundary between one area and another area. IS-IS is best suited for large private networks; it supports larger networks than OSPF. IS-IS is typically used within an ISP and easily supports IPv6 routing.

Latency?

Latency is the delay in transmissions over the path. If latency is used in the cost, a path with higher latency will have a higher cost.

Link utilization?

Link utilization is the percentage of a network's bandwidth that is currently being consumed by network traffic. If utilization is used, the cost will be less for links with low utilization.

What does NAT stand for?

Network address translation

Bandwidth?

Network bandwidth measures the capacity of a link. If bandwidth is a factor in the cost, a link with a lower capacity link will have a higher cost than a link with a high bandwidth link.

Reliability?

Reliability is measured by how often the path is down. If it is used in cost calculations, a highly reliable path will have a lower cost.

Routing Scope

The first way of classifying a routing protocol is the scope. The scope identifies what information is shared and remembered. A private network that is connected to the Internet is known as an Autonomous System, or AS, and is fairly independent from the Internet. The only thing that is really shared is the link to the Internet. Businesses or organizations that connect their private network to the Internet are assigned a unique autonomous system number, or ASN. Usually, the ASN is handled by the ISP. The routing protocol scope identifies boundaries where routing information is shared

What is Proxy ARP?

This document explains the concept of proxy Address Resolution Protocol (ARP). Proxy ARP is the technique in which one host, usually a router, answers ARP requests intended for another machine. By "faking" its identity, the router accepts responsibility for routing packets to the "real" destination. Proxy ARP can help machines on a subnet reach remote subnets without the need to configure routing or a default gateway.

Exterior routing?

Exterior routing is done between autonomous systems. Organizations that connect their private network to the internet are assigned a unique autonomous system number, or ASN.

Throughput?

Although the advertised bandwidth is the maximum capacity of a link, its actual throughput will be less due to latency and other network overhead. If used in the cost calculation, larger throughput will contribute to a lower cost.

What are the reserved IP addresses

• 10.0.0.1 to 10.255.255.254 • 172.16.0.1 to 172.31.255.254 • 192.168.0.1 to 192.168.255.254

Link State?

1. Link state protocols are also known as shortest path first protocols. The following is the general process employed by a router that uses link state protocols for finding best hop information. 2. The router examines its directly connected network links and assigns a metric value. o The metric value is based on the status and connection type of the link. o The metric value may also include other factors, such as bandwidth and delay. 3. The router determines the neighbor routers that are connected by each direct network link. 4. The router builds a link-state packet (LSP) that contains a list of its neighbors and the metric value of the link to that neighbor. 5. Through a process called flooding, the router sends the LSP to its neighbor routers. 6. Neighboring routers, in turn, sends the LSP to its neighbors, and so on. o To eliminate looping, each router forwards the packet to every neighbor except the one it received the packet from. o A smart flooding algorithm prevents looping when there are circular routing paths. 7. Using converged route information, the router constructs a complete map of the routing topology. 8. From this map, the router will calculate the best path to each destination network. o Best path is determined using Dijkstras's algorithm, which calculates the shortest path first. 9. Using the link-state protocol, the router uses the best path information to insert next hop information for each network path into the routing table.

EGP

An Exterior Gateway Protocol, or EGP, is used to share routing information between autonomous systems. For example, a routing protocol used within the Internet to route data between Internet routers and into autonomous systems runs as a protocol that is classified as an EGP. As a network administrator, you will mostly work with IGP routing protocols. The only situation where you would work with EGP is if you had a very large network connected to the Internet.

IGP

An Interior Gateway Protocol, or IGP, is a routing protocol that is used within an Autonomous System.Within your private network you would run a routing protocol to share internal routes. This is an interior gateway protocol

What is BGP?

Border Gateway Protocol BGP is an advanced distance vector protocol (also called a path vector protocol). BGP is an exterior gateway protocol (EGP) used for routing between autonomous systems. • BGP uses paths, rules, and policies instead of a metric for making routing decisions. • BGP is a classless protocol. • Internal BGP (iBGP) is used within an autonomous system; External BGP (eBGP) is used between autonomous systems. BGP is the protocol used on the internet; ISPs use BGP to identify routes between autonomous systems. Very large networks can use BGP internally, but typically share routes on the internet only if the AS has two (or more) connections to the internet through different ISPs.

Dynamic NAT?

Dynamic NAT automatically maps internal IP addresses with a dynamic port assignment. On the NAT device, the internal device is identified by the public IP address and the dynamic port number. Dynamic NAT allows internal (private) hosts to contact external (public) hosts, but not vice versa—external hosts cannot initiate communications with internal hosts. This implementation is also sometimes called many-to-one NAT because many internal private IP address are mapped to one public IP address on the NAT router.

Troubleshoot: Can't access outside local subnet

If one or more hosts can communicate only with hosts on the local subnet, the problem is likely with the default gateway configuration. • If a single host is having problems, check the default gateway setting on that host. • If multiple hosts are having problems, check the default gateway setting and verify that the DHCP server is configured to deliver the correct default gateway address. • If all hosts have the same problem and the default gateway setting is correct, verify that the default gateway server is up and configured for routing.

What is routing metrics?

If there are multiple paths to a distant network, a routing protocol will assign a metric to each directly connected network link. The metric value can be thought of as the cost of sending a packet over that link. The metric is used when determining the best path to a network.

Interior routing?

Interior routing is done within an autonomous system (AS). An autonomous system is a private network that is somewhat independent of the internet. The only thing that is shared is the link to the internet.

What is a loopback entry?

Loopback entries contains loopback addresses which are used for diagnostics and for troubleshooting the TCP/IP stack. Loopback interfaces are always available. They will continue to run even if other physical interfaces in the router are down.

Dynamic routing?

Maintaining static only routing in a large network with multiple routers would be very difficult, especially when there are multiple network paths that an IP packet can take to get to its destination. Routers can dynamically learn about networks by sharing routing information with other routers. • Dynamic routing is implemented by enabling a routing protocol. • A routing protocol adds dynamic entries to the routing table. • If multiple paths to a network are available, routing protocols define: o The algorithm used to calculate a metric. o How routers communicate with each other to share network path information. • Routing protocols use metric information to insert the best hop into the routing table when multiple paths are available.

How does NAT work?

NAT works by translating private addresses to the public address of the NAT router. • Hosts on the private network share the IP address of the NAT router or a pool of addresses assigned for the network. • The NAT router maps port numbers to private IP addresses. Responses to internet requests include the port number appended by the NAT router. This allows the NAT router to forward responses back to the correct private host. • Technically speaking, NAT translates one address to another. Port address translation (PAT) associates a port number with the translated address. o With only NAT, you would need a public address for each private host. NAT associates a single public address with a single private address. o PAT allows multiple private hosts to share a single public address. Each private host is associated with a unique port number on the NAT router. o Because virtually all NAT routers perform PAT, you normally use PAT, and not just NAT, when you use a NAT router. (NAT is usually synonymous with PAT.) NAT supports a limit of 5,000 concurrent connections.

What is Port Forwarding?

One commonly used implementation of static NAT is called port forwarding. Port forwarding allows incoming traffic addressed to a specific port to move through the firewall and be transparently forwarded to a specific host on the private network. Inbound requests are addressed to the port used by the internal service on the router's public IP address (such as port 80 for a web server). This is often called the public port. Port forwarding associates the inbound port number with the IP address and port of a host on the private network. This port is often called the private port. Based on the public port number, incoming traffic is redirected to the private IP address and port of the destination host on the internal network.

What is OSPF?

Open Shortest Path First OSPF is a link state routing protocol used for routing within an AS. • OSPF uses relative link cost (shortest path) for the metric. • OSPF is a classless protocol. • OSPF divides a large network into areas. o Each autonomous system requires an area 0 that identifies the network backbone. o All areas are connected to area 0, either directly or indirectly through another area. o Routes between areas must pass through area 0. • Internal routers share routes within an area; area border routers share routes between areas; autonomous system boundary routers share routes outside of the AS. • A router is the boundary between one area and another area. OSPF is best suited for large private networks.

Packet loss?

Packet loss occurs when IP packets fail to reach their destination. If it is used in calculating cost, a link that experiences greater packet loss will have a higher cost.

What is RIP?

Routing Information Protocol RIP is a distance vector routing protocol used for routing within an autonomous system (such as an IGP). • RIP uses hop count as the metric. • RIP network size is limited to a maximum of 15 hops between any two networks. A network with a hop count of 16 indicates an unreachable network. • RIP v1 is a classful protocol; RIP v2 is a classless protocol. RIP is best suited for small private networks.

How does routing work?

Routing is the process of moving packet from one network to another using routers. To perform routing, a router: • Receives a frame • Opens the frame's payload, which is an IP packet • Reads the packet header to find IP addressing information • Matches the destination network address with entries in its routing table creates a new frame using the packet as a payload • Transmits the new frame to the next hop gateway.

Distance vector routing?

Set a metric value or cost based on how far away a network is. o Are generally measured by hop count. o May measure distance by delay, packets lost, or something similar. • Set a direction that is associated with the distance. o Direction refers to the network interface that is used to forward the IP packet to the distant network. When using a distance vector protocol, a router: • Will only share information with its direct neighbors (the next hop routers). • Will share all route information that it knows about. o Directly connected routes o Routes learned from its direct neighbors • Will send route information at a regularly scheduled time

Static NAT (SNAT)?

Static NAT maps a single private IP address to a single public IP address on the NAT router. Static NAT is used to take a server on the private network (such as a web server) and make it available on the internet. Using a static mapping allows external hosts to contact internal hosts—external hosts contact the internal server using the public IP address and the static port. This implementation is called one-to-one NAT because one private IP address is mapped to one public IP address. In addition to static NAT, the term SNAT also means source NAT, stateful NAT, and secure NAT. Although the terms vary, the function is the same.

Static routing?

Static routing entries are manually added to the routing table. • A route entry of 0.0.0.0 identifies the default entry or default route which is special form of a static entry. • Static entries remain in the routing table until they manually removed. • When changes to the network occur, static entries must be modified, added, or removed. • Static routing works well in smaller networks.

What is a default route?

The default route is an entry of 0.0.0.0 in a routing table. This entry matches every network. If no other entry in the routing table matches the destination IP address in a packet, the router will send the packet to the gateway found in the default route. • The gateway identified in the default route is known as the default gateway. • If a default route does not exist, the router will drop any packets that do not match an entry in a routing table.

Hop count?

The distance between networks can be measured in hop counts, or the number times a router forwards an IP packet from one network to another. For a directly connected link, the hop count will be zero.

Load?

The load on a router refers to the amount of computational work that it performs. If load is a factor in the cost, links for routers that are performing under heavy load will have a higher cost.

MTU?

The maximum transmission unit (MTU) setting on a router determines the maximum payload size for a frame. While this characteristic is not usually included in a metric, it is sometimes used as a tie-breaker when two links or paths have the same cost.

What is a routing table?

The routing table is a database of entries, each with: • The address of a known network • The next hop gateway (router) • The network interface to reach the next hop gateway • A metric or cost that indicates the desirability of the route (The lower the metric, the more desirable the route.)