Skip to main content

Check if jumbo frames are working

This is a simple post showing how to test if large MTU is working in your network using ping tool:

When jumbo frames are not enabled in all networking devs:

# ping -s 8000 -M do -c 5 172.16.64.75
PING 172.16.64.75 (172.16.64.75) 2000(2028) bytes of data.
From 172.16.64.68 icmp_seq=1 Frag needed and DF set (mtu = 1500)
From 172.16.64.68 icmp_seq=1 Frag needed and DF set (mtu = 1500)
From 172.16.64.68 icmp_seq=1 Frag needed and DF set (mtu = 1500)
From 172.16.64.68 icmp_seq=1 Frag needed and DF set (mtu = 1500)
From 172.16.64.68 icmp_seq=1 Frag needed and DF set (mtu = 1500)

--- 172.16.64.75 ping statistics ---
0 packets transmitted, 0 received, +5 errors

And with enabled jumbo frames:

# ping -s 8000 -M do -c 5 172.16.64.75
PING 172.16.64.75 (172.16.64.75) 8000(8028) bytes of data.
8008 bytes from 172.16.64.75: icmp_seq=1 ttl=64 time=0.461 ms
8008 bytes from 172.16.64.75: icmp_seq=2 ttl=64 time=0.360 ms
8008 bytes from 172.16.64.75: icmp_seq=3 ttl=64 time=0.402 ms
8008 bytes from 172.16.64.75: icmp_seq=4 ttl=64 time=0.410 ms
8008 bytes from 172.16.64.75: icmp_seq=5 ttl=64 time=0.347 ms

--- 172.16.64.75 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 3998ms
rtt min/avg/max/mdev = 0.347/0.396/0.461/0.040 ms

Upgrading Dell PowerConnect 54xx switch firmware

This is the procedure I’ve used to upgrade the firmware of my PowerConnect 5448 and 5424 switches. You should have set up a tftp server in same network as switch admin ip is. There are plenty of howtos to do this in the web like this, so I assume that you have already running the tftp server.

First, connect to to your switch via ssh or serial cable and enable privileged commands:

> enable

Copy new firmware from your tftp server:

# copy  tftp://tftp_server_ip/switch/powerconnect_54xx-20046.ros image
# copy tftp://tftp_server_ip/switch/powerconnect_54xx_boot-2000.rfb boot

Now, you should view the new firmware image ready, but not active:

# show bootvar
Image  Filename   Version     Date                    Status
-----  ---------  ---------   ---------------------   -----------
1      image-1    1.0.0.31    31-Oct-2007  10:32:13   Active* 
2      image-2    2.0.0.46    14-Apr-2011  13:10:53   Not active

"*" designates that the image was selected for the next boot

Select image-2 as active for the next boot:

# boot system image-2

The image is selected as active for the next system boot

# show bootvar
Image  Filename   Version     Date                    Status
-----  ---------  ---------   ---------------------   -----------
1      image-1    1.0.0.31    31-Oct-2007  10:32:13   Active  
2      image-2    2.0.0.46    14-Apr-2011  13:10:53   Not active*

Now, we only have to reload the switch to boot with updgraded image.

# reload

I’ve upgraded several switches and in all of them the switch configuration has been preserved.

Access to your switch or router through serial cable

To access to your switch or router through a serial cable you can use tools like kermit or minicom.

To access with kermit in a debian machine you can simple install it with:

# apt-get install ckermit

To run kermit I use this config file in my home directory

$ cat .kermrc
set carrier-watch off
set handshake none
set flow-control none
set line /dev/ttyS0

Once you have connected the serial cable on ttyS0 you can run kermit command:

$ kermit
C-Kermit 8.0.211, 10 Apr 2004, for Linux
 Copyright (C) 1985, 2004,
  Trustees of Columbia University in the City of New York.
Type ? or HELP for help.
(/user/) C-Kermit>

Now, simple type connect kermit command to access to your router:

(/user/) C-Kermit>connect
Connecting to /dev/ttyS0, speed 9600
 Escape character: Ctrl-\ (ASCII 28, FS): enabled
Type the escape character followed by C to get back,
or followed by ? to see other options.
----------------------------------------------------

Router>

This is simple way to access to your router or switch and configure it.


Notice: Undefined variable: wp_sh_class_name in /var/www/elkano.org/blog/wp-content/plugins/wp-syntaxhighlighter/wp-syntaxhighlighter.php on line 1002

Notice: Undefined variable: wp_sh_class_name in /var/www/elkano.org/blog/wp-content/plugins/wp-syntaxhighlighter/wp-syntaxhighlighter.php on line 1002

Warning: Use of undefined constant XML - assumed 'XML' (this will throw an Error in a future version of PHP) in /var/www/elkano.org/blog/wp-content/plugins/wp-syntaxhighlighter/wp-syntaxhighlighter.php on line 1048