Very excited to announce I was invited to participate in Networking Field Day #9.
The first question is: What is Networking Day? Well it is an event where we (networkers) get to participate, listen, and interact with various different vendors.
And I’ll be joining a great group, a few of which I’ve met at the last few Cisco Live’s and some of which I’ll be meeting for the first after many interactions on Twitter and the Web.
- Bob McCouch
- Brandon Carroll
- Brandon Mangold
- Charles Galler Jr.
- Ivan Pepelnjak
- Jody Lemoine
- John Herbert
- Jonathan Davis
- Jordan Martin
- Lindsay Hill
- Nick Buragilo
- Pete Welcher
- Me – Steve Occhiogrosso
Which vendors will be at Networking Field Day #9, well there will be a few of them:
This looks like a very interesting line-up It’s got some bigger players and some newer players that look to be offering some very intriguing products products. Everything from ‘SDN WANs’ to Network Monitoring.
This whole event will be streamed live so you can watch as everything unfolds! I’ll post the link soon!
Hard to be believe 2014 is gone and and 2015 is here! Yea I know we are already a few days into 2015 but hey for some reason I still hear people saying “Happy New Year”, much like I still Christmas decorations out.
So what’s in store in for 2015!? Well we are going to find! I got a few things on my punch list: (always got to keep thinking ahead right?!)
- Finish my CCNP: Data Center
- Knock out the WCNA, Wireshark Certified Network Analyst. Figure by now I’ve got a decent amount of time clocked using Wireshark
- Maybe brush up on some wireless technologies, my CWNA is about a year an half old now and renewal is slowly creeping up. Or maybe look at the CCNP: Wireless, but I don’t think that track has been updated in a while.
- Deepen my knowledge of Voice.
- Been debating on expanding the videos available on this blog. Or maybe even doing a podcast, I’ve bouncing the idea off the wall for quite some time now. Of course the term podcast might be an over-statement I’m thinking of maybe some recording technical discussions amongst friends.
It’s always nice to reflect on the past and what 2014 provided:
- CiscoLive 2014 San Francisco, met up with a great people again and had a blast, learning some new things in the process!
- Twitter – Got to admit Twitter is always fun and amazing resource. Big shout-out to the people that make my twitter entertaining and and lively!
- Cisco Champions – Interacting with another great group of networking enthusiasts is always a great experience!
- Exams!! I Think I knocked out 7-8 exams last year, finishing off my CCNP: Security, getting my CCNA: Data Center and falling one exam short of my CCNP: Data Center. I’m really starting to think the toughest part of getting a certification is acting finding the time to make it to testing center! But boy was 2014 a busy year.
- SolarWinds Thwack Ambassador, got to post articles involving VoIP Monitoring & Troubleshooting for month over at Thwack. Being able to interact with a community that great was a real treat in itself!
- 27 New posts went up on this blog, that is honestly much more than I thought I did, putting me well past the 100 post mark!
- I might need to a running count on the number of bottles of Whisk(e)y I drink this year.
- Too much more to even mention!
Here’s to 2015!
As I was going through some CiscoLive365 sessions (Remember CiscoLive365 is great!) just this last weekend I came across the slides for BRKSEC-2028 – Deploying Next Generation Firewall with ASA & Firepower services. Unfortunately there is no video for this session yet but the presentation slides are there and luckily the slides are detailed enough so you can easily follow along with the content. One the slides that stood out of to me was where the new FirePower modules (Hardware or Software) falls into the order of operations as traffic passes through the ASA. Screenshot below:
I think the big call-outs here are:
- The FirePower module will not actually drop the traffic itself, the traffic gets ‘marked’ if the traffic is to be dropped. All the traffic that passes to the FirePower module will indeed get passed right back to the ASA and it is the responsibility of the Cisco ASA to actually drop the traffic.
- Even existing connections still get inspected if the security policy demands.
- ACL’s and XLate entries will filter traffic before the traffic even makes it to the FirePower module.
- This is only slightly different from how the existing IPS Module inspects traffic from ASA. In regards to the flow path.
Definitely some good information to know when building out your new policies.
I don’t know about you but when I find myself performing packet captures and analyzing PCAPs I usually only know the symptoms of the issue I am attempting to troubleshoot. IE: Connection timeouts, slow response, long transfer times, etc. I usually don’t know much more than that, only in rare occasions do I get a heads up and insight into the behaviors of the application I am trying to troubleshoot. For all the other situations I need to rely on the PCAPs and interpret what and how the applications are communicating. Whether or not the application is behaving properly and performance is as it should be or if there is indeed something amiss somewhere.
Now for me the easiest way to do this is by using the reviewing the ‘Summary’ page under the ‘Statistics’ menu. A sample summary page is below:
A few great call-outs from this screen:
- Packet Size Limit -Knowing whether or not the packets within the capture were sliced after the first so many bytes is important to know, as sometimes you might not see the entire TCP header or wireshark will start classifying the packets as malformed. Although you will also see a ‘Truncated’ message within the packet indicating the packet was sliced.
- First Packet, Last Packet, & Elapsed time -Matching up the time of a packet capture with when the particular issue occurred is crucial, after all you don’t want to find yourself analyzing the wrong capture. The Elapsed time is important to make note of as this give you the ability to establish a baseline, knowing how long a process takes can you help you identify an issue or identify expected behavior in the future.
- Avg. Packet Size – Depending on what you are trying to troubleshoot the average packet size can be a quick indicator in regards to whether or not your fully using the MTU an your network. If you are troubleshooting data transfers normally you would expect the Avg. Packet to be quite large. If you see exceptionally small packet sizes data transfers may take a lengthy amount of time due to the increase TCP overload and normal L3 forwarding. Same goes for the Avg Mbit/sec, if you have large packets flowing you can expect to see a higher throughput rate, and the opposite for lower packet size rate.
The next spot that is worth checking out is the ‘Conversations’ which is also found under ‘Statistics’ this quaint little window gives you a brief overview of any Source/Destination devices identified within the capture. From an L2 Ethernet perspective up to a L4 TCP/UDP Perspective allowing you see what end points are really involved with this communication along with how much data was sent, the length of time the connection, etc. It’s not completely unheard of for applications to communicate with other devices (Web Servers, DB Servers, File Servers, Other App Servers) to perform whatever tasks it is trying to perform and it could be very possible this third server may or may not be slowing down the process.
So by using these two windows in Wireshark you’ve identified the following:
- The length of time the process take. – Found in the elapsed time of the capture, as long as the entire process was captured that is.
- The endpoints involved with this communication. – Remember it is important to cut down as much background noise as possible.
- How much data is transferred and at what size & rate. – This can very helpful when working data transfers.
There are many different fields in the various headers we get to examine during packet analysis, one of the most overlooked field is the IP Identification field. This simple 16-bit field is displayed in Hex and has a few different uses, most importantly:
- Identifies fragmented packets.
- Identifies the individual packets that the sender transmits.
How does this help us?
- Well, by reviewing the IP Identification numbers you can easily identify which packet was dropped in the conversation, by comparing the packet captures from two different capture points.
- This field can also give us a glimpse at how busy the end-devices are. The IP Identification field will increase by ‘1’ for every packet from the sender. Remember the IP ID Value is specific to each individual and not to a specific conversation. If you are following a specific conversation we may see consecutive IP ID #’s or we could see large jumps in the IP ID # intervals. Depending on the numbers this could tell us if the end-devices could be overloaded, or under-utilized and depending on the situation that could point us to a smoking gun.
- If the packets get fragmented they will have the same IP ID number, the Fragment Offset field will also be set as well. This is helpful in following a conversation over particular link changes.
- Seeing the same IP ID #’s in the same packet capture could also identify switching or routing loops within our network. The IP ID #’s will always increase, seeing the duplicate numbers means were are seeing the same packet more than once. The first thing you want to do is verify your capture point is functioning properly and make sure your capture point is in the right spot. Once you verified that it’s time to go hunting for the loop.
By reviewing the IP ID numbers of the packets what can we tell about this conversation with Wireshark.org?
- All the IP ID #’s are unique, no routing/switching loops
- The IP ID #’s are pretty consecutive on both sides of the conversation. Showing both endpoints are not being highly utilized at this point in time. In fact there are one or two gaps on the 192.168.1.4 side of the conversation showing that endpoint is a little busier than 18.104.22.168
Ever so often when I was doing some packet analysis I would come across systems that were sending packets larger the Ethernet MTU of the segment. Or so I thought those packets were getting transmitted, eventually I finally figured out why I was seeing packets with an increased packet size.
The answer was large segment/send offload (LSO) – When this feature is enabled it is the responsibility of NIC Hardware to chop up the data ensuring why it conforms to the MTU of media/network segment.
Now that we know why we are seeing these large packets, the next part of the question is how are we seeing these large packets in Wireshark. Well, Wireshark relies on WinPCAP or LibPCAP depending on your platform, these two tools capture the packets just before the packets hit the NIC Card and get transferred to the actual network.
The above image is from Winpcap.org, showing the kernel level NPF just above NIC Drive, thus explaining how Wireshark is able to see the larger traffic. Before it hits the NIC Driver and gets segmented due to its LSO capabilities.
Ever so often I find myself troubleshooting some type of wireless related issue, and while wireless issue’s vary from
- Slow performance
- Clients can’t connect
- Poor voice performance
- Or even random disconnects, the list is endless.
However one of the common things I hear during the troubleshooting process is without a doubt along the lines of:
“But it says I have an excellent signal with five bars!”
And…. my favorite question in response to that statement is:
“What is your data rate?” (usually with this same expression)
Signal strength is only a small piece to the puzzle what determining whether or not you have a good quality signal strength. The signal strength indicator itself could even be misleading, just because a client is registering ‘5 bars’ with a good RSSI and SNR does not necessarily mean the AP on the other end of the connection is seeing a similar RSSI & SNR to the WLAN Client. Do I hear a transmit power mismatch, or a highly reflected RF environment?
Nowadays WLAN clients comes in all shapes and sizes (Phones, Tablets, wireless scanners, VoIP handsets) long gone are the days of wireless is just for laptops. With this wide array of hardware clients, you can guarantee each of these devices have a wireless transmitter with different specifications, and while it is impossible to take into account every WLAN client, the client audience should be considered when designing a WLAN or deploying AP’s.
Consider the an access point is transmitting at it’s max power rating, you can guarantee the wireless phone or VoIP handset does not have that same power level. It’s like two people trying to communicate with each other that across a football field and only one person has a mega-phone. The other guy without the megaphone will need to probably repeat himself a few times for the other person to understand him (Think of that as Data Retries).
One of the better ways to identify a proper Wireless connection would be to verify the the data rate, and see review the data rate statistics. Many of the different WLAN Client software have this functionality, telling us what percentage of the data was transmitted/received at a specific data rate. Now shifting data rates is common in a WLAN, but seeing 90% of data operating at the 1, 2, or 5.5 Mbps data rate is just poor performance.
A while back I posted about Understanding a wireless connection, and I wanted to dive a bit deeper and expand on the concept (albeit years later, but hey better late then never right?)