review the key networking concepts tcp/ip reference model ethernet switched ethernet ip, arp tcp
DESCRIPTION
Review the key networking concepts TCP/IP reference model Ethernet Switched Ethernet IP, ARP TCP DNS. FTP data can be infinitely large, when do we chop it into smaller Units?. Internetworking devices Repeaters: PHY device that restores data and collision signals Hub: Multiport repeater - PowerPoint PPT PresentationTRANSCRIPT
• Review the key networking concepts– TCP/IP reference model– Ethernet – Switched Ethernet– IP, ARP– TCP– DNS
• Internetworking devices– Repeaters: PHY device that restores data and collision
signals
– Hub: Multiport repeater
– Bridge: Datalink layer device connecting two or more collision domains (extended LAN). MAC multicasts are propagated throughout the extended LAN
– Switch: Multiport bridge with parallel paths
– Router: Network layer device.
– Network address translator (NAT): Transport layer device.
– Gateways: Transport layer or application layer devices
• Ethernet– Shared medium LAN technology– Need medium access control
• CSMA/CD + binary exponential backoff
– Frame format:
|Preamble|Start|Dst Addr|Src Addr|length| Data | Pad |Checksum 7 1 6 6 2 0-1500 0-46 4
• Minimum data + pad length: 46 bytes
• Maximum data length: 1500 bytes
• Fast Ethernet (100Mbps)– Reduce cable length and keep everything else– Duplex mode
• Gigabit Ethernet (1000Mbps)– Reduce cable length and increase minimum
frame size– Duplex mode
• Switched Ethernet– Get dedicated link in Ethernet in a transparent
manner.– Issue: the switch needs to know where to
forward a packet– How is it accomplished?
• Self-learning algorithm to obtain the location of each machine
• Forwarding algorithm
– Can switched Ethernet take advantage of the dense connectivity in the network topology?
• Spanning tree algorithm
• IP– Addressing
(type, network number, host number)
• Class A, Class B, Class C
– Classless inter-domain routing• IP address + prefix length
e.g. 192.168.0.3/22
• IP header format:– Version (4 bits): IPv4, IPv6– Header length (4 bits): in 32-bit words, min
header is 5 words or 20 bytes– Type of service (8 bits): reliability, precedence,
delay, and throughput. Used in DiffServ (IP QoS support)
– Total length (16 bits): header + data in bytes, total must less than 64 KB.
– Identifier (16 bits): uniquely identify the datagram during its life for a given source and destination addess.
• IP header format:– Flags (3 bits): more flag, no-fragmentation
– Fragment offset (13 bits): in units of 8 bytes
– Time to live (TTL): specified in router hops
– Protocol: next level protocol to receive the data
– Header checksum: 1’s complement sum of all 16 bit words in the header
– Source/destination address: original source/destination
– Options (variable): Security, source route, record route, timestamp recording
– Padding (variable): makes header length a multiple of 4
– Data (variable): data + header <= 65535 bytes.
• IP functionality:– Framentation– Addressing– Routing is done by other protocols
• IP router– Routing: computes the next hop for each
destination.– Forwarding: based on the destination address in
an IP packet, forward the packet to the right next hop
• Longest prefix matching
• Internet Routing protocols– RIP: distance vector algorithm– OSPF: link state algorithm– BGP: path vector algorithm that supports policy
based routing
TCP segment structuresource port # dest port #
32 bits
applicationdata
(variable length)
sequence number
acknowledgement numberReceive window
Urg data pnterchecksum
FSRPAUheadlen
notused
Options (variable length)
URG: urgent data (generally not used)
ACK: ACK #valid
PSH: push data now(generally not used)
RST, SYN, FIN:connection estab(setup, teardown
commands)
# bytes rcvr willingto accept
countingby bytes of data(not segments!)
Internetchecksum
(as in UDP)
• TCP header– Source port (16 bits): identifies the source
process. 20=FTP, 23=Telnet, 80=HTTP.– Destination port (16 bits)– Sequence Number (32 bits): Sequence number
of the first byte in the segment. If SYN is present, this is the initial sequence number (ISN) and the first data byte is ISN+1
– ACK number (32 bits): Next byte expected– Data offset (4 bits): number of 32-bit words in
header– Reserved (6 bits)
• TCP header– Control (6 bits):
• URG urgent pointer field significant
• ACK: ACK field significant
• PSH: push function
• RST: reset the connection
• SYN: synchronize the sequence number
• FIN: no more data from sender
– Window (16 bits): wil accept [ack] to [ack+window]
– Checksum (16 bits): cover the header plus a pseudo header.
• TCP header– Urgent pointer (16 bits): points to the byte
following urgent data.– Options (variable): max segment size, window
scale factor, etc.
• Each computer has a name resolver routine (gethostbyname in UNIX)
• Each resolver knows the name of a local DNS server
• Resolver sends a DNS request to the server• DNS server either gives the answer,
forwards the request to another server, or gives a referral– Recursive query / iterative query
• Referral = next server to whom the request should be sent