Capturing 802.11 Frames in Wireshark

Figured I would pass this along. I started reading chapter 15 in the CCNP Switch certification Guide; Integrating Wireless LANs. While reading the first few pages, I quickly wanted to get a sniffer out and check out all of these 802.11 frame specifications that it references.

Some examples are DIFS(duration timer) and the random back off timer.  I decided to fire up Wireshark, but the frames kept appearing as 802.3(Ethernet) frames. This is known as "fake" Ethernet headers. Unfortunately, with the current WIFI card installed in my laptop, I won’t be able to sniff  802.11 traffic.  

Per Wire Shark:
Without any interaction, capturing on WLAN's may capture only user datapackets with "fake" Ethernet headers. In this case, you won't see any 802.11 management or control packets at all, and the 802.11 packet headers are "translated" by the network driver to "fake" Ethernet packet headers.

http://wiki.wireshark.org/CaptureSetup/WLAN

You can also download a 802.11 capture and learn how to read it by following this document.

http://www.cse.ust.hk/~muppala/csit5610/labs/Wireshark_labs/Wireshark_802_11.pdf


 

Keeping Current as a Network Engineer & Working your way to becoming a Network Architect

Keeping Current:
It’s crucial to always stay current in any industry that you work in. You want to be the one bringing new ideas to the table and possibly have new solutions to common problems that companies face. Some of the following websites I follow to keep myself current in the Network Industry along with the Data Center Industry are below.

http://www.datacenterknowledge.com/
 
http://www.networkworld.com/topics/lan-wan.html

Certifications are also a great way to keep current and enhance your skill sets.

Working your way to becoming a Network Architect:
My long term goal is to become a Network Architect and I have found that reading a ton of White Papers along with test results from third party vendors is going to greatly help me achieve this goal. Cisco puts out some great white papers on proven design guides that I highly recommend for anyone to read. The following link is a perfect example and yes I read the entire white paper along with others.

http://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/HA_campus_DG/hacampusdg.html

This has helped me tremendously in being able to design a better network and with my CCNP studies. Cisco also has another great resource, it’s called Cisco Validated Design Program. Check out the following link, its design guides for pretty much every type of network. These are proven and tried design guides from true industry experts.

http://www.cisco.com/en/US/netsol/ns741/networking_solutions_program_home.html

Reading benchmark or test results is another great way to get a key understanding on how to evaluate a product before you buy it and what to look for in new hardware.  I follow this website and a majority of Vendors put third party evaluation results on their own website.

http://www.networktest.com/

9 Common Spanning Tree Mistakes

Great read on STP common mistakes. Article is from 2013.

http://www.networkworld.com/community/blog/9-common-spanning-tree-mistakes?

Interface-Range Command on Non Contiguous Ports

Ever needed to make changes to multiple interfaces that are not within the same range? I know I have and always wondered how to update interfaces that were not sequntially ordered. Here is how.

We need to create a macro and then invoke it before we apply our changes.

Creating the macro:

Cisco_4948E_01#config t
Cisco_4948E_01(config) define interface-range joel GigabitEthernet1/20 , GigabitEthernet1/22 , GigabitEthernet1/24

Invoking the Macro: This now put us into interface configuration mode

Cisco_4948E_01(config)#interface range macro joel
Cisco_4948E_01(config-if-range)#
Cisco_4948E_01(config-if-range)#description macro-test

Verification that our change were successful:

Cisco_4948E_01#show interfaces description | include macro-test
Gi1/20                         down           down     macro-test
Gi1/22                         down           down     macro-test
Gi1/24                         down           down     macro-test

RSTP sync process.

Great write up on RSTP sync process.

http://routemyworld.com/2009/06/19/bcmsn-rstp-convergence-changes-and-compatibilty/

Upgrading an ASA5520 - IOS Upgrade 9.1

In order to create a port-channel between an ASA5520 and a 4948 I needed to upgrade the code. The process is very simple to say the least. For some reason I expected it to be difficult. The process I followed is below.

1. Confirm the feature set you are looking for is supported in the new code and look for any new potential gotchas. Its is customary to request a BUG SCRUB from Cisco before deploying any new code.

http://www.cisco.com/en/US/docs/security/asa/asa91/configuration/general/asa_91_general_config.html

2. Download the code from the Cisco portal.

3. Confirm you have enough space for the new code. Use the DIR command.

Cisco-ASA5520-01# dir

Directory of disk0:/

129    -rwx  16275456     06:03:42 Jan 30 2011  asa821-k8.bin
130    -rwx  11348300     09:15:52 Jan 30 2011  asdm-621.bin
6      drwx  4096         00:03:46 Jan 01 2003  log
13     drwx  4096         00:03:54 Jan 01 2003  crypto_archive
14     drwx  4096         00:04:28 Jan 01 2003  coredumpinfo
132    -rwx  12105313     09:13:20 Jan 30 2011  csd_3.5.841-k9.pkg
133    drwx  4096         09:13:24 Jan 30 2011  sdesktop
134    -rwx  2857568      09:13:26 Jan 30 2011  anyconnect-wince-ARMv4I-2.4.1012-k9.pkg
135    -rwx  3203909      09:13:26 Jan 30 2011  anyconnect-win-2.4.1012-k9.pkg
136    -rwx  4832344      09:13:28 Jan 30 2011  anyconnect-macosx-i386-2.4.1012-k9.pkg
137    -rwx  5209423      09:13:30 Jan 30 2011  anyconnect-linux-2.4.1012-k9.pkg
118    -rwx  3080         13:40:55 Dec 05 2012  8_2_1_0_startup_cfg.sav
255582208 bytes total (170237952 bytes free)

4. Upload the code onto the device via tftp. Use the following command copy tftp disk0:/ and you will be prompted for the ip address of the tftp server, source file name, and press enter unless you want to change the name of the file once its uploaded, I never do. Confirm the MD5 key with what was show on the Cisco website.

5. Change your boot statement and confirm it took. I always like to setup two statements in case there are any issues with the first IOS code.;

config t
boot system disk0:/asa911-k8.bin
boot system disk0:/asa821-k8.bin
end
!
WR
!

Cisco-ASA5520-01# show bootvar

BOOT variable = disk0:/asa911-k8.bin;disk0:/asa821-k8.bin
Current BOOT variable = disk0:/asa911-k8.bin;disk0:/asa821-k8.bin;disk0:/end
CONFIG_FILE variable =
Current CONFIG_FILE variable =

6. Save your configuration and reload the device with the reload command.

7. Confirm your new code is running with the show version command.

Cisco-ASA5520-01# show version

Cisco Adaptive Security Appliance Software Version 9.1(1)
Device Manager Version 6.2(1)

Compiled on Wed 28-Nov-12 10:38 by builders
System image file is "disk0:/asa911-k8.bin"
Config file at boot was "startup-config"

Cisco ASA Oversubscription - Maximizing Throughput (ASA 5550) Part 1

This week I ran into an oversubcription issue on an ASA5550. To alleviate the issue, we followed the recommendations below from Cisco. I am including some of the conditions I saw before the change. Keyword is Alleviate, depending on your traffic rates you might resolve the problem going this route. In other cases, you would just have to get a second pair or firewalls to segregate traffic or just upgrade to 10GB. The best way to determine this is to place a sniffer between the ASA and drill down as close to the microsecond to see the microbursts on the line and data rate patterns.

Maximizing Throughput (ASA 5550)

The ASA 5550 has two internal buses providing copper Gigabit Ethernet and fiber Gigabit Ethernet connectivity. For Slot 1 (Bus 1), you can use either the copper ports or the fiber ports. The copper ports are enabled by default.

For maximum throughput, configure the ASA so that traffic is distributed equally between the two buses. Lay out the network so that traffic enters through one bus and exits through the other.

For example, the following figure shows the ASA configured so that traffic from the unsecure network and the secure network is evenly distributed between Bus 0 and Bus 1. Traffic from hosts on the secured network flows through interface 0/0 on Bus 0 to hosts on the unsecured network. Traffic from hosts on the unsecured network flows through interface 1/0 on Bus 1 to hosts on the secured network.

http://www.cisco.com/en/US/docs/security/asa/quick_start/5500/5500_quick_start.html#wp35995 

 

On the ASA you can issue the show traffic command and near the end of the output you will see the following output. Ideally you would want this to be balance. In this case, both of the oversubscribed interfaces were both on Slot 0.

Show Traffic 
----------------------------------------
 Per Slot Throughput Profile (1 minute)
----------------------------------------
  Packets-per-second profile:
    Slot 0:      12654  89%|********************************************
    Slot 1:       1603  11%|*****

  Bytes-per-second profile:
    Slot 0:    1649003  76%|**************************************
    Slot 1:     511183  24%|************

On the interface level, you would see the Underruns counter increment along with the Overruns counter (See below). To try and alleviate or resolve this issue move one of the ports to Gi1/X and mmonitor it over a few days.

Per Cisco:

Interface overruns, no buffer and underruns often show that the firewall cannot process all the traffic it is receiving on its NIC. Overruns and no buffers indicate that input traffic is too much on a given interface. The interface maintains a receive ring where packets are stored before they are processed by the ASA. If the NIC is receiving traffic faster than the ASA can pull them off the receive ring, the packet will be dropped and either the no buffer or overrun counter will increment. Underruns behavior similarly but deal with the transmit ring instead.

ASA5550/act# show interface gigabitEthernet 0/0
Interface GigabitEthernet0/0 "HH", is up, line protocol is up
  Hardware is i82546GB rev03, BW 1000 Mbps, DLY 10 usec
    Auto-Duplex(Full-duplex), Auto-Speed(1000 Mbps)
    Input flow control is unsupported, output flow control is off
    Description: 6509
    MAC address 6400.f182.6770, MTU 1500
    IP address 192.168.168.2, subnet mask 255.255.255.248
    56937880 packets input, 12657181986 bytes, 0 no buffer
    Received 0 broadcasts, 0 runts, 0 giants
    831 input errors, 0 CRC, 0 frame, 831 overrun, 0 ignored, 0 abort
    0 pause input, 0 resume input
    0 L2 decode drops
    33686564 packets output, 5457717040 bytes, 577125 underruns
    0 pause output, 0 resume output
    0 output errors, 0 collisions, 0 interface resets
    0 late collisions, 0 deferred
    0 input reset drops, 0 output reset drops, 0 tx hangs
    input queue (blocks free curr/low): hardware (255/230)
    output queue (blocks free curr/low): hardware (255/0)
  Traffic Statistics for "HH":
    56937881 packets input, 11616408550 bytes
    34263689 packets output, 5097504222 bytes
    12365 packets dropped

ASA5550/act# show interface gigabitEthernet 0/1
Interface GigabitEthernet0/1 "HM", is up, line protocol is up
  Hardware is i82546GB rev03, BW 1000 Mbps, DLY 10 usec
    Auto-Duplex(Full-duplex), Auto-Speed(1000 Mbps)
    Input flow control is unsupported, output flow control is off
    Description: 6509
    MAC address 6400.f182.6771, MTU 1500
    IP address 192.168.1.1 subnet mask 255.255.255.0
    24794625 packets input, 4336231091 bytes, 0 no buffer
    Received 4648 broadcasts, 0 runts, 0 giants
    0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
    0 pause input, 0 resume input
    0 L2 decode drops
    40981082 packets output, 3012528711 bytes, 1614642 underruns
    0 pause output, 0 resume output
    0 output errors, 0 collisions, 0 interface resets
    0 late collisions, 0 deferred
    0 input reset drops, 0 output reset drops, 0 tx hangs
    input queue (blocks free curr/low): hardware (255/230)
    output queue (blocks free curr/low): hardware (255/0)
  Traffic Statistics for "HM":
    23737668 packets input, 3724976676 bytes
    42595724 packets output, 2342955016 bytes
    6597 packets dropped