Network Plus Part 3 - The World of TCP/IP

How many hosts are available with a CIDR of /25 through /30?

/25 - 126. /26 - 62. /27 - 30. /28 - 14 /29 - 6. /30 - 2

How many networks are available with a CIDR of/25 through /30?

/25 - 2. /26 - 4. /27 - 8. /28 - 16. /29 - 32. /30 - 64

What are the well-known port numbers?

0 through 1,023.

What are the 3 private IP address ranges?

1) 10.x.x.x 2) 172.16.xx to 172.31.xx 3) 192.168.x.x

What are 2 problems with distance vector routing?

1) It uses hop count, which is not always an accurate way to determine metrics. 2) The routing table updates sent between routers are sent at predetermined intervals, so there might be a change between routers that has not yet been communicated to the neighbor routers.

What are 2 benefits to link state routing over distance vector routing?

1) LSA's send updates to other routers, rather than sending entire routing tables, which is faster and uses less bandwidth. 2) Link state routing tables are updated faster, decreasing the time for total convergence between routers.

What are the 4 things that can affect routing metrics?

1) Maximum Transmission Unit, or MTU. 2) Network bandwidth. 3) Cost. 4) Latency.

What are the 4 steps for a computer to get an IP address from DHCP?

1) The computer boots up and sends out a DHCP discover broadcast. 2) DHCP sends a unicast DHCP offer via the requesting computer's MAC address. 3) The computer receives the DHCP offer and responds with a DHCP request saying that it agrees to use the DHCP configuration that was offered. 4) DHCP responds with a DHCP acknowledge and then stores that computers IP configuration.

In a router's routing table, at a bare minimum, what 4 columns of information will be included?

1) The network address, such as 192.168.15.0. 2) The subnet specific to that network, such as 255.255.255.0. 3) The Gateway, which is 0.0.0.0 if the router is directly connected to that network. 4) The IP address of the router's interface that is connected to that network.

What is the Loopback address used by IPv4?

127.0.0.1

What is the Loopback address used by IPv6?

::1

What is Address Resolution Protocol, or ARP?

A broadcast that is sent over a network to match a known IP address with an unknown MAC address.

What type of port number information is included in an IP packet?

A destination port number that is determined by the type of application that you are using. The source port number is assigned by the system that sent the packet, and it can be any arbitrary port number, other than the well-known port numbers.

What is Open Shortest Path First, or OSPF?

A dynamic, interior gateway protocol that uses link state protocol. It uses link state advertisements between routers to update routing tables, using bandwidth as the primary factor to determine metrics.

What is a static route in a router or other TCP/IP enabled devices?

A route that is manually entered, rather than dynamically generated.

What type of device would you use port forwarding for?

A security camera or some other device that did not get a lot of consistent traffic. If you did it with a web server or something like that, it would create too much of a demand on the router.

What is the link between 2 routers considered?

A separate, private subnet. Static IP routes can be set in those routers to shuttle traffic back and forth so hosts on those different networks can use each other's resources.

What is port triggering?

A way to set up a router so that if traffic goes out on one port, such as port 21 for FTP, to allow that traffic back into the network if it comes back on a different port, such as port 20, which is the port that FTP responds on..

How are autonomous systems related to EGP vs. IGP dynamic routing?

All communication inside an autonomous system is done using IGP, and any communication that is outside of the AS is done using EGP.

What is Dynamic NAT, or DNAT?

Also known as Pooled NAT, it is when there are a fixed number of NAT IP addresses configured on a router, instead of everyone using the same one.

What is an expired IP address?

Although DHCP leases for IP addresses normally renew themselves when the lease is expired & the computer is restarted, it is possible that an IP address can expire, but then not be able to reach DHCP for some reason to get a new IP address.

What is Routing Information Protocol, or RIP?

An interior gateway, distance vector protocol that is one of the oldest dynamic routing protocols, but it is still used in smaller networks that don't change very often.

What is an Autonomous System, or AS?

Any given organization that has control over all of the routers that affect their network.

In a subnet mask, what is the signifigance of ones and zeroes?

Anywhere in the subnet mask that has a one is a value that can't be changed. If there is a zero, those numbers can be changed. In 255.255.255.0, the first 3 octets can't be changed, but the last octet can be.

How does network bandwidth affect routing metrics?

As traffic traverses different networks, it can be slowed down as it moves through hardware or network mediums that do not support higher transmission speeds.

What is APIPA?

Automatic Private IP Addressing is what a computer does when it cannot reach a DHCP server while trying to get IP configuration information. It is an IP address like 169.254.x.x, which is not a publicly routable IP address.

What is the Linux equivalent to Dynamic Host Control Protocol, or DHCP?

BOOTP, or Bootstrap Protocol.

Name 4 things you will likely find on a SOHO router that you won't find on an enterprise-level router.

Built-in switches, firewalls, WAP's, and web-based interfaces.

What is a scenario when 2 hosts in a network might end up with the same IP address, creating duplicate IP addresses in that network?

Certain hosts like printers, servers, etc., are commonly given static IP addresses. If someone manually configures a host, instead of using DHCP, they could inadvertantly choose an IP address that has already been assigned elsewhere.

What are the ranges for Class A, B, and C IP addresses?

Class A) 0 - 126/8 Class B) 128 - 191/16 Class C) 192 - 223/24

What are the 2 methods that dynamic routing protocols use to determine metrics and dynamic routes?

Distance Vector and Link State.

What does On-link mean in the Gateway column of a routing table?

Don't send that traffic through a gateway.

How do you convert the ones and zeroes in the octets of an IPv4 address into dotted decimal notation?

Each of the ones and zeroes matches up from left to right to the numbers 128, 64, 32, 16, 8, 4, 2, 1. If there is a one in the IPv4 address, add that number. If there is a zero, don't add that number. The total is the digit for that octet.

How does the Designated Router, or DR, in OSPF send out LSA's for the network?

Each router sends the DR information using the multicast address 224.0.0.6. The DR sends the network LSA, aka LSA Type 2, to represent the broadcast network to the rest of the OSPF area.

In OSPF, what are Area ID's?

Every router in OSPF is configured to be within a particular Area ID, and that area's designation looks a lot like an IP address, but it has absolutely nothing to do with IP addressing.

How do you view the routing table on a Windows and MAC computer?

From the command line in Windows, use the command "route print" or "netstat -r". On a MAC , go to the /System/Library/CoreServices/Applications folder and then open the Netstat utility.

When finding out how many host addresses are available, why do you have to subtract 2?

In any given range of host addresses, the very first number in that range is always the network ID, and the very last number is always the broadcast address. Every other number is available to be assigned an IP address.

What are the 2 groups that all dynamic routing protocols fall in to?

Interior Gateway Protocols, or IGP, and Exterior Gateway Protocols, or EGP.

What is the metric value in a routing table?

It is a measurement of how long it is estimated for traffic to traverse any given route. By default, routers will always use the route with the lowest number metric to get to any given destination.

In OSPF, how is a Designated Router elected?

It is something that is done automatically between routers running OSPF once their Area ID's have been configured. It can also be configured manually.

What is port range forwarding?

It is the same thing as port forwarding, only you can set up an entire range of ports to forward if you need more than one. An example of that would be setting up a private, multi-user online gaming server.

Is is possible to have duplicate MAC addresses in a network?

It is very unlikely, but if you are using virtual machines that are sometimes manually configured, it is possible to set up more than 1 machine with the same MAC address.

In what domain does a DHCP server need to be in?

It needs to be in the same broadcast domain as the hosts that it will be managing because the hosts send out broadcasted DHCP discover messages when they need IP configuration information. There should only be 1 DHCP server p/broadcast domain.

How does a host on a local network know if a host that it wants to talk to is on the same local network?

It uses its own IP address and subnet mask to compare with the IP address of the other host. If the network ID matches, then the other host is local. Otherwise, the sending host sends an ARP request to the default gateway to get the MAC address of the distant host.

What can you do if your router only supports 2 connections and you want to connect to additional upstream routers?

Many advanced routers allow you to buy and install additional interfaces to add to the total number of connections available.

How does latency affect routing metrics?

Many things, such as distance, can affect latency, which will in turn affect transmission speeds.

How does maximum transmission unit, or MTU, affect routing metrics.

Maximum Transmission Unit affects routing metrics because ethernet traffic traverses different network mediums on the way to its destination, and the frames might have to be modified, which can slow down transmission.

How does Network Address Translation, or NAT, work on a router?

Most networks run on private IP address ranges that are not publicly routable. NAT takes a private, internal IP address, port information, etc., and attaches it's own, public, routable IP address to the packet so it can traverse the Internet.

Do routers only use ethernet?

No, routers can use multiple types of network mediums depending on the connections available on any given router.

Do hosts send out subnet mask information during communications?

No, subnet masks are never sent out from a host.

Do routers care about where an IP packet came from?

No, they only care about where to send it.

Is a routing metric only based on the number of hops between any given router and the destination network?

No, which is why modern routers use a metric count instead of just a hop count to determine the best routes.

Are all IP addresses that are in a DHCP scope automatically available to be assigned to hosts?

Normally, yes. However, you can set up individual or ranges of IP address exclusions to tell the DHCP server to not hand out those IP addresses.

In OSPF, what is a Designated Router, or DR?

OSPF elects a Designated Router (DR) for each broadcast network to act as the main point of contact for the network segment. Each router on the segment becomes adjacent with the DR, which handles all LSAs for the network.

Is DHCP always run off of a separate server or computer?

Often times, yes, but it can also be software that runs on a non-dedicated DHCP machine, such as a router.

Is NAT turned on by default?

On most SOHO routers, yes, and it is sometimes referred to as gateway or router mode. Most enterprise level routers will need to have NAT configured and turned on before it will work.

What is RIP's maximum hop count?

Only 15 hops between networks, so for any network locations further away than that, RIP will not work.

What ports are used by FTP?

Port 21 when reaching out to an FTP server and the server then responds on port 20.

What is NAT also referred to as?

Port Address Translation, or PAT.

What is the 30/30/30 rule when hard resetting a router?

Press in the reset button for 30 seconds while it is powered on, then unplug it for 30 seconds. Press the reset button again, plug it back in, and hold the reset button for another 30 seconds.

How is dynamic routing different than static routing?

Rather than having a single, static route to a destination that could potentially go down, dynamic routing uses metrics to find alternate routes if the preferred route to a destination becomes unavailable.

Describe link state dynamic routing.

Routers using link state routing send out frequent "hello" messages to ensure other routers are still active. They also send out Link State Advertisements, or LSA's, each time there is a change to their routing table.

What do the IP addresses in the Gateway and Interface column of a routing table mean?

Send that traffic through the gateway identified by the IP address, and send it using the device at the Interface IP address.

What is passive mode on an FTP server?

Since FTP receives communications on port 21, and responds on port 20, some routers or firewalls will deny that return communication. Putting the FTP server in passive mode forces it to respond on port 21.

How does RIP use hop counts to determine routes to different networks?

Since it is a distance vector protocol, all routers talking to each other using RIP send their entire routing tables at fixed intervals. RIP only uses the hop count calculated from those tables to determine the best path, and deletes all other routes.

What is a big way that OSPF is better than RIP?

Since it uses link state advertisements, convergence between routers is significantly faster than using RIP, where entire routing tables are sent over preset intervals.

What is the problem with DNAT?

Since there are only a fixed number of IP addresses, only a certain number of hosts in the network can communicate with the outside world at any given time.

Is there any way to use a DHCP server that is not in your local broadcast domain?

Some routers support a function called DHCP relay that can be manually configured to send any local DHCP requests to a distant DHCP server as long as you know its IP address.

When configuring DHCP on a Windows Server, what 3 bits of information do you have to put into the DHCP Scope?

Starting IP address, Ending IP address, and the length of the subnet mask that you want to use.

How does port forwarding work to get past the fact that firewalls will normally block unsolicited traffic?

Static port routes are set up on the router for a network that will automatically forward traffic that comes in on a predesignated port. That port number can be any of the not well-known port numbers, and will allow the traffic past the firewall.

What is important to remember about the ones and the zeroes in a subnet?

Subnets have all ones on the left, and all zeroes on the right.

What does the CIDR notation for the network ID 255.255.0.0/16 mean?

The /16 means that there are 16 ones that makeup the subnet mask, which would also be shown as 255.255.0.0. In other words, the network ID could be any combination allowed by the 255.255.0.0 subnet mask.

What is the IP address and subnet of a default route?

The IP address is 0.0.0.0 and the subnet mask is also 0.0.0.0, meaning that the router doesn't care where the traffic is going - it just sends it to its upstream router.

In any given network, what is the Network ID?

The IP address that identifies the network, and that IP address can't be used by any host on that network. For example, 192.168.60.0 is the network ID for the host 192.168.60.14.

Who is responsible for IP address assignments on the Internet?

The Internet Assigned Numbers Authority, or IANA. They give chunks of IP addresses to regional areas known as Regional Internet Registries who in turn give IP address groups to ISP's.

What is Classless Interdomain Routing, or CIDR?

The ability to further segment subnets down into other network ID's with different numbers of hosts in them in order to better control the number of networks and hosts available in your environment.

Why should you use a not well-known port number when setting up port forwarding?

The device you want to contact probably runs on port 80 or some other well-known port, but by using a different port number, you add in a level of security against hackers who know to scan for the well-known port numbers.

When using subnetting with CIDR, how is the number of hosts affected?

The more you subnet down a network ID, the fewer hosts you will have available. For example, 192.168.35.0/26 will have significantly more hosts than 192.168.35.0/30.

On a router, what is a default route?

The route that a router will send all traffic to if it doesn't know where to send it. This will be that router's upstream router.

What does 0.0.0.0 in the Network Destination and Netmask column of a routing table mean?

The route to any non-specific destination using any non-specific netmask.

What is an upstream router?

The router at an ISP that is the next hop from any given network that is using that ISP to connect to the public Internet.

If your router has more than one connection to upstream routers, how does it know through which connection to send your outgoing traffic?

The router's configuration will include a metric, which is a number that designates the preferred route. The lower the metric, the higher priority that route is.

What is the purpose of private IP addresses?

They are addresses that will never be used to access the public Internet, and they are 100% internal to a private network.

What are the port numbers that sending clients use when sending TCP packets outside of their local network?

They are called ephemeral ports, and they fall in the range of 1,024 through 65,535.

How do routers get packets to networks that aren't in their routing table?

They use ARP to query their upstream router's MAC address, and they send the packet there. The local router doesn't have to know where to send a packet - it only needs to know to send it to its own upstream router.

In OSPF, what is a Backup Designated Router, or BDR?

To avoid the DR as a single point of failure, a Backup Designated Router, or BDR, is also elected for the broadcast network. The BDR also listens to the 224.0.0.6 multicast address and becomes active in case of DR failure.

When subnetting, how do you determine how many networks can be created?

Use 2 to the power of however many bits are available for the network. For example, in a a /27 network, the first 3 bits are available, so 2 * 2 * 2 = 8 available networks.

How can you determine how many host IP addresses are available in any given subnet?

Use 2 to the power of however many host bits are available minus 2. For example, in a /27 network, where the first 3 bits of the last octet are used for the network, there are 5 host bits left. 2 * 2 * 2 * 2 * 2 - 2 = 30 hosts

How is RIP version 2 better than RIP version 1?

Version 1 could only handle classful IP addressing, so CIDR or VLSM networks could not be seen. Version 2 can handle CIDR and VLSM, and also has security enhancements.

When talking about routers, what is Convergence?

When all router tables reflect all routes.

What is Static NAT, or SNAT?

When the NAT configuration on a router recognizes that a device like a web server, print server, etc., has a static IP address that never changes, and keeps that in it's routing table to forward all necessary traffic to that IP address.

What is a rogue DHCP server?

When there is more than one DHCP configured in a broadcast domain, and they compete with each other. This can result in hosts getting assigned IP addresses that don't match other hosts in the network, or that don't allow them to get out to the public Internet.

Describe distance vector dynamic routing.

When using older protocols, such as RIP, routers would send their entire routing table to all of their neighbors, and then each neighbor would compare it to their own in order to determine the best routes.

When are rogue DHCP server problems most common?

When using wireless networks, because wireless routers usually come with DHCP enabled during power-on. Without any configuration, every wireless router in an area will start acting as the DHCP server for that area.

How does cost affect routing metrics?

Whenever possible, the routes that have the lowest cost to traverse will be used.

Is it possible for a router to be connected to more than one upstream router?

Yes, as long as the router has enough ports to support the additional connections. This would be beneficial for redundancy so that if one upstream connection was lost, traffic could still be sent to the other connection.

Can you enable a home DMZ?

Yes, but it is an extreme security risk. You enable it in your router by designating a computer to send all unsolicited traffic from the Internet to. SOHO DMZ's are not the same as enterprise DMZ's and do not have that level of security.

Is it possible for one computer to be able to ping another computer in a local network, but the other computer can't ping back?

Yes, if one of the computers has an incorrect subnet mask.

Does the router WAN connection on a home router get its IP address dynamically, or statically?

You would think it would get a static IP address because it is the direct connection to the outside world, but most WAN connections to ISP's get their IP addresses from the ISP via DHCP.

What is the command line command to see the ARP cache of stored MAC addresses and IP addresses?

arp -a.