21/11/2004 ian/modules/COM342/COM342_L7A.ppt L7A/1/30 COM342 Networks and Data Communications Ian...

21/11/2004 www.eej.ulster.ac.uk/~ian/modules/COM342/COM342_L7A.ppt L7A/1/30

COM342Networks and Data Communications

Ian McCrum Room 5B18

Tel: 90 366364 voice mail on 6th ring

Email: [email protected]

Web site: http://www.eej.ulst.ac.uk

Lecture 7A: Practical TCP/IP Networks


Setting up networking

• Ethernet cards; e.g 3C509 from 3com, in the (very) old days cards were sold as NE2000 compatible. Keypoints are obviously the type of connection at the back, 10BaseT or 10Base2. But is also nice to have flashing lights…

• 10Base2 needs proper T-pieces and terminators. A simple daisy chain is used, with cables at least 2 metres long. My stack of PCs made for cramped cabling so I have now swopped for twisted pair (10BaseT).

• 10BaseT needs proper cables, these can be straight ( or normal) or they can be crossover types, PC <->hubs use straight but Hubs <-> network sockets on the wall need crossover types.

• It is possible to link two PCs without using a hub, but you must use a crossover cable.

• The lab in week 12 is to do with making up 10BaseT leads.


In Windows you can see how many packets pass through your network card


We get other information from running utilitiesE.g From START->RUN->CMD (or command.com) IPCONFIG/ALL

……

Physical Address. . . . . . . . . : 00-03-47-B8-53-21

DHCP Enabled. . . . . . . . . . . : Yes

Autoconfiguration Enabled . . . . : Yes

IP Address. . . . . . . . . . . . : 192.168.0.3

Subnet Mask . . . . . . . . . . . : 255.255.255.0

Default Gateway . . . . . . . . . : 192.168.0.1

DHCP Server . . . . . . . . . . . : 192.168.0.1

DNS Servers . . . . . . . . . . . : 192.168.0.1

Lease Obtained. . . . . . . . . . : 21 November 2004 11:12:30

Lease Expires . . . . . . . . . . : 22 November 2004 11:12:30

The machine at 192.168.0.1 is a windows 98 box running “ICS” internet connection sharing. It actually passes DNS queries on to my ISP. The LAN is not aware of anything beyond this router. It can surf and connect using SSH or ftp. I run zonealarm on the router and am careful not to run “servers” within the LAN.


Simple LANs

If we ignore the internet for the minute then all we must do is link all PCs to our LAN. This is straight forward

Then possibly to another LAN.

First you need to recall data about IP numbers and netmasks

All must be on the same network, the network part of their IP number

router


IP Numbers

• The first half of the available range for Ipv4 is taken up with Class A machines. 8 bits are used for the network

• The next quarter is class B, 16 bits are used for the network. And the last quarter (roughly) is class C where 24 bits are used for the network portion.

• An example Class-C is 193.61.142.120 with a netmask of 255.255.255.0 This can also be described as 193.61.142.120/24

• You are allowed to use 192.168.0.0 to 192.168.255.255 for you own use without registering it. These special private addresses cannot be put onto the internet. Of course what you do in the privacy of your own home, your own LANs is your own business…

• There are also class A and class C numbers reserved for private addresses. E.g 10.0.0.0 to 10.255.255.255 and there are also a few other funny numbers used here and there…


Setting up addresses

• If you are setting up a machine on a LAN administered by someone else you must either.

• Get the IP number and netmask as well as the IP number of the gateway and the IP number of the DNS server from the network administrator. He might want to know what physical network socket you are plugging into, or even the MAC number burnt onto your network card (NIC). Remember Lab 2; you can use IFCONFIG /all to get that.

• Or if he is using Dynamic Host Control Protocol ( DHCP) then you just tick the “automatic boxes”


TCP/IP on my machine


My IP no 193.61.148.83

• What can we determine about it?– Since it is in the range 192.0.0.0 to 223.255.255.255

1100-0000 0000-0000 0000-0000 0000-0000– It must be a class C address

• Where 1st 3 bits identify that it is class C

• Next 21 bits identify network ( one of 2 millionish)

• Last 8 bits host within network.


http://www.ripe.net/index.html


•193.61.128.00 /14

•193.61.159.255 range for UUJ

•1100 0000 | 0011 1101 | 1000 0000 | 0000 0000 = 193.61.128.0

•1100 0000 | 0011 1101 | 1001 1111 | 1111 1111 = 193.61.159.255

•(159-128)*256 = 7936 addresses

•193.61.160.00 /14•193.61.175.255 range for UUC

•1100 0000 | 0011 1101 | 1010 0000 | 0000 0000 = 193.61.160.0

•1100 0000 | 0011 1101 | 1010 1111 | 1111 1111 = 193.61.175.255

•(175-160)*256 = 3840 addresses


1111 1111 | 1111 1100 | 0000 0000 | 0000 0000 = 255.252.0.0 mask (aggregate entry in CIDR) sometimes depicted as \14 since the first 14 bits are set to 1.

1100 0000 | 0011 1101 | 1001 0100 | 0101 0011 = 193.61.148.831111 1111 | 1111 1100 | 0000 0000 | 0000 0000 = 255.252.0.01100 0000 | 0011 1100 | 0000 0000 | 0000 0000 = 193.60.0.0 it’s a match!

The first fourteen bits must be identical to those in red in order that an IP address be routed in this direction.

Hence UUJ has

From:1100 0000 | 0011 1101 | 1000 0000 | 0000 0000 = 193.61.128.0

To:1100 0000 | 0011 1101 | 1001 1111 | 1111 1111 = 193.61.159.255


Getting your own IP number

Whoever connects you to the internet must look after routing your traffic, they must give you a number from the bank of numbers that they adminster

They can give you one static number or a range of static numbers, these will be related and involve some sort of netmask, at least partially. E.g UUJ

Most home users will be given one number, usually allocated dynamically, the number can change and will be different every time you switch on or reboot

My ISP charges £2 extra for a static IP number


Setting up your own domain

• You can buy vacant domain names from e.g Simply.com. There will be a yearly fee, about a tenner for a .com and less for a .co.uk or .org I’ll not cover the “naming schemes here” look it up.

• Once you know the IP number of the machine you are going to use you can tell the seller to give you a “redirect” from his machines. Traffic for your named machine will get your number

• There are a few places that will give you a free name, if it is within their realm. E,g I have mccrum.homelinux.com the site www.dyndns.org owns this (and 48 other domains).

• This site also allows you to change the destination IP number yourself, or better still automatically. My ISP gives me an IP number for the machine at my house, but he can change it. There is a small program running on my router PC that monitors this and re-registers the new number at dyndns.org (see dyndns for details)


Talking across LANs

• Consider that I, on 193.61.148.83 with subnet mask

255.255.255.0, wish to talk to Mary on 193.61.149.46.

• Since my subnet mask defines that all with addresses

193.61.148.0 to 193.61.148.255 as local

• this packet to 193.61.149.46 will be passed to a router

(gateway) on 193.61.148.200


Note the route has two NICs one for each network

Router

Me Mary

193.61.148.00/24 193.61.149.00/24

Packet


My IP address193.61.148.83

Mary’s IP address193.61.149.46

My MAC address

Router’s lhs MAC address

IP

MAC

Source Destination

First step forward to route and stored there


Router

Me Mary

193.61.148.00/24 193.61.149.00/24Packet

Packet in router and passed up to IP layer


My IP address193.61.148.83

Mary’s IP address193.61.149.46

Mary’s MAC address

IP

MAC

Source Destination

Second step rebuild packet and forward to Mary

Router’s rhs MAC address


Router

Me Mary

193.61.148.00/24 193.61.149.00/24

Packet

Packet passed to Mary


Routing tables

Use the following commands to see the routing tables; In Linux route –n is useful in windows try ROUTE PRINT…

Network Destination Netmask Gateway Interface

0.0.0.0 0.0.0.0 192.168.0.1 eth0

127.0.0.0 255.0.0.0 127.0.0.1 loopback

192.168.0.0 255.255.255.0 192.168.0.3 eth0

192.168.0.3 255.255.255.255 127.0.0.1 loopback1

192.168.0.255 255.255.255.255 192.168.0.3 eth0

224.0.0.0 224.0.0.0 192.168.0.3 eth0

255.255.255.255 255.255.255.255 192.168.0.3 eth0

Default Gateway: 192.168.0.1

Router

Me Mary

192.168.0.3/24192.168.111.2/24

Packet

192.168.0.1/24192.168.111.1/24


In the Linux world

• Many routers, including the wireless ones that combine hubs and/or ADSL modems or interfaces for modems use linux as an embedded OS. You can access these, either by pointing a browser at the machine, possibly/typically using an unusual port number (not 80!) or by using Telnet or the more secure version SSH.

• Windows users must download a SSH client (e.g PUTTY) but telnet and a web browser are already.

• It is easy to configure an old PC as a router, either with two ethernet cards or more usually, one ethernet card and one ADSL modem or simple wireless access point.

• If your wireless AP has a built in hub for 10BaseT then you can use it.

• The decision is whether to split your home into two LANs or persevere to get one working.

• Some knowledge of firewalls is also required since your AP or even combined ADSL modems and routers will offer this.


In the Linux world, a simple router

• An basic understanding of Linux will require reading a few hundred pages…it is almost possible to configure linux by clicking various readymade gui tools but at some stage you WILL have to check and maybe edit a few text files. You will need to have a simple terminal window open to do this and know a few commands {ls –l , cd dir, cd .., cat file, vi file (:wr, :q! etc)}

• Assuming the two ethernet card network (the rest are similar). Know which cards you are using, easier if different types!

• When linux boots it searches for hardware and if it finds the cards it inserts various modules of code into its kernel, it can also get hints by looking at the file /etc/modprobe.conf if you examine the boot log (run dmesg) it can help

• First thing to do is check that the correct modules to drive your ethernet cards have been inserted, use the lsmod command for this (look at man lsmod)

• Then use the ifconfig –a and route –n commands to check all is ok

• ping is your friend.


Examples of linux commands (for 3C509 and 3c905B PCI card)

• I identified the cards by (a) reading the labels and (b) running the lspci command from a linux terminal

• modprobe eth0 3c59x ;I found 3c5x9.o in /lib/modules/ I also checked the Ethernet_HOWTO at www.tldp.org for guidance on 3Com network cards.

• I had to boot a dos floppy that contained 3C5x9cfg.exe to set the cards transceiver type to 10BaseT and enable plug and play. Further docs are found in /use/src/linux

• ifconfig eth0 192.168.0.1• ifconfig eth1 192.168.111.1• route add –net 192.168.0.0 netmask 255.255.255.0 eth0 • route add –net 192.168.111.0 netmask 255.255.255.0 eth1• route add default gw 192.168.111.200 ; router passes rest to ADSL modem• Few other miscellaneous things to do, enable forwarding in the kernel. This

involves either recompiling or writing a ‘1’ to a “file” in /proc I.e echo 1 > /proc/sys/net/ipv4/ip_forward

• Also to make changes permanent you need to either invoke the commands above on powerup (in one of the rc scripts) or use your linux distribution configuration files, e.g /etc/sysconfig/network


Summary; what you should know

• A lot of the preceding detail is only for your interest.• Know about IP numbers, what range each class takes• Know that there are private IP addresses that are not

routed, at least on the public internet• Realise that one LAN can be linked to another through a

router that has two NICs• Realise that each LANs IP network addresses must be

different to allow routing.• Realise that routing tables must have “routes” for each

destination address, LAN1, LAN2 and the rest of the word. You do NOT need to know the details…


Final version

• And when I get my wireless router it is going to get worse!

• Thank goodness for linux!

• A good overview of Pat Sweeney’s cable modem setup is contained in lecture COM342_L7B

router Router, with USB modemAlso does IP Masquerading

21/11/2004 ian/modules/COM342/COM342_L7A.ppt L7A/1/30 COM342 Networks and Data Communications Ian...

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