NetworkTut is a small export company .This firm has an existing enterprise network that is made up exclusively of routers that are using EIGRP as the IGP. Its network is up and operating normally. As part of its network expansion, NetworkTut has decided to connect to the internet by a broadband cable ISP. Your task is to enable this connection by use of the information below.
Connection Encapsulation: PPP
Connection Type: PPPoE client
Connection Authentication: None
Connection MTU: 1492 bytes
Address: Dynamically assigned by the ISP
Outbound Interface: E0/0
You will know that the connection has been successfully enabled when you can ping the simulated Internet address of 172.16.1.1
Note: Routing to the ISP: Manually configured default route
Answer and Explanation:
Enter the outbound e0/0 interface to enable PPPoE and bind the dialer profile 1 to this interface:
R3(config)#interface e0/0
R3(config-if)#pppoe enable
R3(config-if)#pppoe-client dial-pool-number 1 (interface E0/0 is bound to the logical dialer 1 interface)
R3(config-if)#no shutdown
R3(config-if)#exit
Create and configure the dialer interface of the router R3 for PPPoE with a maximum transmission unit (MTU) size of 1492 bytes and a negotiated IP address (dynamically assigned)
R3(config)#interface dialer 1 (define a dialer rotary group and enters interface configuration mode)
R3(config-if)#ip address negotiated
R3(config-if)#ip mtu 1492
R3(config-if)#encapsulation ppp
R3(config-if)#dialer pool 1
R3(config-if)#exit
The "ip address negotiated" command instructs the client to use an IP address provided by the PPPoE server (using DHCP).
The "dialer pool 1" command associates the dialer back to the "pppoe-client dial-pool-number 1" on the Ethernet interface. Notice that the pool numbers must match on the Ethernet interface and the dialer interface for the configuration to operate.
Manually configured a default route on router R3
R3(config)#ip route 0.0.0.0 0.0.0.0 dialer 1
R3(config)#exit
Try pinging the simulated Internet address
R3#ping 172.16.1.1
The ping should work well and you will receive replies from the simulated Internet address.
Save the configuration
R3#copy running-config startup-config
For your understanding:
The reason why we need to configure the MTU size to 1492 bytes is:
When a user requests a web site, a client/server negotiation occurs between the PC and the web server that hosts the web site. During the negotiation, a maximum MTU size is negotiated. Since the PC negotiates and its default MTU size is 1500 bytes (Windows 3x, 9x, NT, ME, and so forth), the web server negotiates an MTU size of 1500 bytes. Therefore, regardless of the MTU size you configure on the router, the web server still sends packets up to 1500 bytes in size.
The reason why some pages do not fully load is that the router fragments IP packets if the PC MTU is misconfigured and a packet greater than 1492 bytes is sent to the router. This fragmentation does not occur on the return path through the universal access concentrator (UAC) (Cisco 6400 or 7200). When the UAC receives a packet greater than 1492 bytes, the packet is dropped, and the UAC generates and sends an Internet Control Message Protocol (ICMP) message to the web server that sent the oversized packet. The ICMP informs the web server that it sent an oversized packet and that it needs to resend the packet with a smaller MTU.
The problem occurs because many web servers block ICMP messages, which causes the server to continuously send 1500-byte packets. These packets are dropped, and as a result, the requested web site does not load. If the web server is properly configured and ICMP messages are not blocked, the server adjusts its MTU and retransmits until the page loads completely.
A partially loaded page occurs when the initial data packets sent from the web server are under the 1492 byte maximum. However, a packet is then sent that exceeds this maximum. The server continues to retransmit this oversized packet that results in a partially loaded page and a "waiting for reply..." message in the status bar.
(Reference: http://www.cisco.com/en/US/tech/tk175/tk15/technologies_tech_note09186a0080093bc7.shtml)
