All rights reserved cisco public ite 1 chapter 6 18

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© 2006 Cisco Systems, Inc. All rights reserved. Cisco Public ITE 1 Chapter 6 18 Services and Protocol: Port Number Domain Name System (DNS) - TCP/UDP Port 53 –TCP is used for "zone transfers" of full name record databases, while UDP is used for individual lookups. Hypertext Transfer Protocol (HTTP) - TCP Port 80 Simple Mail Transfer Protocol (SMTP) - TCP Port 25 –SMTP is a long established Internet protocol that is used for the delivery and receipt of e-mail. Post Office Protocol (POP) - UDP Port 110 –POP3 is only to collect e-mail –To collect e-mail you have a choice of POP3 or SMTP. However, you can only use SMTP with software that is SMTP aware such as Microsoft Exchange. Outlook and Outlook Express cannot on their own receive e-mail using SMTP. –When configuring your e-mail software (e.g. Outlook or Outlook Express) you always need to specify the name or IP address of the SMTP server for outgoing e-mail. Telnet - TCP Port 23 Dynamic Host Configuration Protocol - UDP Port 67 File Transfer Protocol (FTP) - TCP Ports 20 and 21
© 2006 Cisco Systems, Inc. All rights reserved. Cisco Public ITE 1 Chapter 6 19 Services and Protocol: Port Number Dynamic Host Configuration Protocol - UDP Port 67 and 68 When a system starts up on a network it must first request an IP address (assume it is not using a static IP address), and it does this by broadcasting a request to the DHCP server: UDP 0.0.0.0:68 -> 255.255.255.255:67 –since the requesting system doesn't have an IP address (why it is asking) it uses 0.0.0.0 and since its new to the network it doesn't know where the DHCP server is, so it broadcasts the request to the entire network (255.255.255.255). The DHCP server then responds with something like: UDP 192.168.1.1:67 -> 255.255.255.255:68 –This is typically a DHCP offer. NOTE it has to be broadcasted (255.255.255.255) as the requesting system doesn't yet have an IP address (its contained in the offer). The data in this transmission contains the IP and other network configuration information that the requesting system needs to connect to the network (lease time, Subnet Mask, etc). Sometimes you will see something like: UDP 192.168.1.101:67 -> 192.168.1.1:68 –as a request, followed by a reply UDP 192.168.1.1:68 -> 192.168.1.101:67 –These are typically IP renewal requests, where a system has an IP address and is asking to renew it (ie get the lease extended). Since the requesting system knows where the DHCP server is and it already has a current IP address the requests don't need to use 0.0.0.0 and 255.255.255.255.
© 2006 Cisco Systems, Inc. All rights reserved. Cisco Public ITE 1 Chapter 6 20 DNS In data networks, devices are labeled with numeric IP addresses, so that they can participate in sending and receiving messages over the network. –However, most people have a hard time remembering this numeric address.

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