Packet filtering
router
Packet filter routing
Inside LAN Outside LAN
Check outgoing packets Check incoming packets
acan send to bonly via application Gateway.
Example: e-mail can decide what to do
Application
gateway
Firewalls
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Application Layer Protocols - Computer Networks - Lecture Slides, Slides of Computer Networks
Some concept of Computer Networks are Aloha Ethernet, Application Layer Protocols, Basic Building Blocks, Computer Networking, Content Free Protocols, Medium Access Sub Layer, Packetised Filetransmission. Main points of this lecture are: Application Layer Protocols, Application, Application Gateway, Incoming Packets, Outgoing Packets, Domain Name Systems, Machines, Exploding Internet, Impractical, Hierarchical Domain
Typology: Slides
2012/2013
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Packet filteringrouter
Packet filter routing
Inside LAN
Outside LAN
Check outgoing packets
Check incoming packets
a can send to b only via application Gateway.Example: e-mail can decide what to do
Application
gateway
Firewalls
•Originally hosts text fetched by all machines at night
•Exploding Internet•Impractical
•Hierarchical domain based naming scheme
•distributed DBMS
for implementing the same
- Map host names and e-mail destination to IP addresses
resolver DNS server
UDP packets
IP address
Now application makes TCP connections to the IP address
Domain Name Systems
Insertion into the tree
Example: Insert peacock into iitm.ac.in
Permission from admin at iitm.ac.in
Database in the form of resource records for each host/domain
When a resolver gives a domain name to DNS,
It gets back resource records associated with that name
Domain name case insensitive
Component can be upto 63 characters long
hiphens allowed
- #? …… not allowed
Domain Name System (contd.)
Resource record is a five type:Domain name
TTL
Type
Class
Value
Domain to whichrecord applies
Stability ofrecord
In
ASCII, number/a domain name
Internal
SOA – Primary source of information above NSs zone
A – IP address
MX – Name of domain prepared to accept email for
specified
domain
NS – Name server for this domain
CNAME – Aliases for a name: cs.iitm & iitm same domain
NS – Name server for this domainCNAME – Aliases for a name: cs.iitm & iitm same domainPTR – Alias for IP addressMINFO – Pentium III, unixMtech 2k.com 86400 IN MX peacock.iitm.ernet.inEntry in the com dBArrangement with peacock to collect mail delivered to
Mteck2k.com Send mail for Mtech2k.com to peacock.iitm.ernet.inDial up and collect mail
Domain Name System (contd.)
Each zone contains some part of the tree and authoritative nameserver for that zone
int
com
edu iitm
aero
cs
speech
donlab
sun
eng