CS 480 M01 Lecture Notes 17 - Nov 2, 2022

Previously

Ch 13: TCP/IP Networking
Managed by ... ICANN, ISOC , IETF ...
Network Standards and Documentation: RFCs, FYIs, BCPs, STDs
OSI Model
TCP/IP Protocol Suite and Network Model
Layers (Application, Transport, Network, Link, Physical)
Packets & encapsulation: Ethernet, IP, TCP, Application
Ethernet, TCP, UDP, and IP Headers
Maximum Transfer Unit (MTU)
Ethernet, CSMA/CD, Switches v. Hubs
Packet Addressing (MAC, IP (+ARP), hostnames (+/etc/hosts, DNS), Ports ( /etc/services)
Address Types (Unicast, Multicast, Broadcast, Anycast)
IP Addresses: IPv4 address classes (A,B,C,D)
IP subnetting and netmask
Local traffic (destination directly reachable on the same ethernet segment) vs traffic through a router

Ch 13: TCP/IP Networking Continued

IP address crisis
CIDR: Classless Inter-Domain Routing
CIDR allows the network portion to be made smaller than would be implied by an address’s implicit class. Aggregating several networks for purposes of routing => "supernetting"
Private Addresses and NAT
Private Addresses that will never be globally allocated and can be used internally by any site:


A	10.0.0.0	10.255.255.255	10.0.0.0/8	(1x)
B	172.16.0.0	172.31.255.255	172.16.0.0/12	(16x)
C	192.168.0.0	192.168.255.255	192.168.0.0/12	(256x)

NAT - network address translation on the border router (sharing single external address)
IPv6

Routing

Routing Tables
in kernel, includes masks - the most specific entry is picked
old(er)

root@itest:/etc/rc.d# netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.8.0     0.0.0.0         255.255.255.0   U         0 0          0 eth0
127.0.0.0       0.0.0.0         255.0.0.0       U         0 0          0 lo
0.0.0.0         192.168.8.1     0.0.0.0         UG        0 0          0 eth0

new(er)


root@itest:/etc/rc.d# ip route show 
default via 192.168.8.1 dev eth0 
192.168.8.0/24 dev eth0  proto kernel  scope link  src 192.168.8.3 
 

            if default router set

ip route add default via 192.168.8.1 dev eth0
ip route show
 

Static v. Dynamic Routing - command route v. routing daemon
ICMP redirects

Open Ports

old(er)

netstat -a

new(er)

ss

ARP: the Address Resolution Protocol

old(er)

root@itest:/etc/rc.d# arp -a
lbc.cs480.cs.nmsu.edu (192.168.8.1) at 00:1b:21:56:d9:d4 [ether] on eth0

root@itest:/etc/rc.d# ping -c 1 ben
PING ben.cs480.cs.nmsu.edu (192.168.8.12) 56(84) bytes of data.
64 bytes from ben.cs480.cs.nmsu.edu (192.168.8.12): icmp_seq=1 ttl=64 time=0.233 ms
	
--- ben.cs480.cs.nmsu.edu ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.233/0.233/0.233/0.000 ms

root@itest:/etc/rc.d# arp -a
ben.cs480.cs.nmsu.edu (192.168.8.12) at 00:0f:20:37:29:5f [ether] on eth0
lbc.cs480.cs.nmsu.edu (192.168.8.1) at 00:1b:21:56:d9:d4 [ether] on eth0

new(er)

# ip neigh
192.168.8.1 dev eth0 lladdr 00:50:56:c0:00:02 REACHABLE
# ping -c 1 andres2
PING andres2 (192.168.8.61) 56(84) bytes of data.
64 bytes from andres2 (192.168.8.61): icmp_seq=1 ttl=64 time=2.33 ms

--- andres2 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 2.335/2.335/2.335/0.000 ms
# ip neigh
192.168.8.61 dev eth0 lladdr 00:50:56:23:02:f7 REACHABLE
192.168.8.1 dev eth0 lladdr 00:50:56:c0:00:02 REACHABLE

Sending an IP Packet to Another Host

On the same subnet v. Going through a router ...

DHCP

Security Issues

Basic Configuration

lab ...

next - Chapter 16: Domain Name Service (DNS)