Lab Objective:
Learn how jumbo frames work and configure an interface to send them.
Lab Purpose:
Ethernet traffic is encapsulated inside frames. The maximum size (MTU) of this frame is 1500 bytes. Any packet larger than this is referred to as a jumbo frame. An interface receiving a jumbo frame can either fragment it or drop it unless it’s configured to receive them.
Please configure your interfaces for jumbo frames only after speaking to your equipment vendor because it may actually slow your network down.
Lab Tool:
Packet Tracer
Lab Topology:
Please use the following topology to complete this lab exercise:
Lab Walkthrough:
Task 1:
Connect the above network devices. Use a crossover cable to connect the routers.
Task 2:
Change the hostnames as indicated and add the IP addresses. Here is the config for R0.
Router>en
Router#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#host R0
R0(config)#int f0/0
R0(config-if)#ip add 192.168.1.1 255.255.255.252
R0(config-if)#no shut
R0(config-if)#end
Task 3:
Check the maximum transmission unit for the Ethernet interface. It should be 1500 bytes.
R0#show int f0/0
FastEthernet0/0 is up, line protocol is down (disabled)
Hardware is Lance, address is 0060.3e01.9601 (bia 0060.3e01.9601)
Internet address is 192.168.1.1/30
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Full-duplex, 100Mb/s, media type is RJ45
[Output Truncated]
Task 4:
Change the MTU. Different models and interface types may give different options. Here are your options for this model. Match the configuration on R1.
R0(config)#int f0/0
R0(config-if)#mtu ?
<64-1600> MTU size in bytes
R0(config-if)#mtu 1600
Task 5:
Unfortunately, Packet Tracer’s sniffer is somewhat limited, but below are two Wireshark packet captures for an Ethernet frame. The top is normal, and the bottom is a jumbo frame showing how much data it contains. The bottom capture is from two Ethernet frames, which normally would never be able to move this volume of data.
Image copyright: samsclass.info
Task 6:
You can set jumbo frames on your network card if it supports them.
Notes:
On a live router, you could run a ping test, telling the router not to fragment the ping packet or change its size. Below is the ‘do not fragment’ option.
Type of service [0]:
Set DF bit in IP header? [no]: Yes
There is a nice jumbo frame lab at the URL below if you want to capture the packets for real on your home or virtual network.
