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Category: Switch

Check if jumbo frames are working

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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

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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

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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.