Category: Networking

This will be a brief article but a good one. It will save you some walking time to server room. I have the need to capture traffic on the switch or on the router several times every week. That action needed from me to be physically near the switch and to configure SPAN port so that I can connect to the switch with my machine and capture some packets with wireshark. Okay, I could use RSPAN to get captured packets to the closest switch but this altogether is not good enough. It’s too time consuming for short packets captures in troubleshooting sessions.

Recently in my CCIE study I came across the info that Cisco IOS is able to capture packets on the device itself and on more interfaces in once. You can later export that capture to your PC and analyze it with wireshark.

You can do it like this

Now that my topology in GNS3 is exactly as in INE Workbook 1 I can share it with you if you don’t want to do all the basic configurations and connections by yourself.

After spending too much money on different rack rentals in the past few months I decided that I will definitely need to try to use GNS3 for simulating my CCIE labs. It will be the only solution if I didn’t want to spend all my money and then have no more left to pay myself trip to Cisco HQ.

After one whole day of struggling with different GNS3 issues I did succeed to configure almost everything. From now I am able to use GNS3 for almost all chapters of my loved INE Workbook VOL.1 and probably VOL.2 also.

There are some things that are not available on GNS3 simulated IOS and I will try to list them below at some point. Other thing that took me some time are that the interfaces are named differently. Cisco Etherswitch Module is added to router in GNS3 order to simulate some basic switch features that is normally not available in GNS3. There is no way to use 0/0 – 0/21 port names on that Etherswitch Module. The interfaces are 1/0 – 1/15 so you cannot do nobrainer paste of config to those “switch” devices. Some serial interfaces are for example Serial 0/0 and in the workbook they are Serial 0/0/0 so this is another one. There are furthermore some other changes to witch interfaces are different devices connected but all the devices now are connected to all other devices exactly as in VOL.1 physical topology. This file down there is prepared for BGP lab chapter of INE Workbook 1. but keep in mind that it can be good for all other parts of the Workbook as the interface configuration is not changed across the Workbook 1 so you just need to modify routing to get started with other chapters.

Do the topology by yourself, you will learn more!

We will speak here about some basics about Forwarding UDP broadcast traffic. If you were wondering what Forwarding UDP broadcast traffic actually is I will try to explain it here in few words.

If you have more that one broadcast domains in your local network, let’s say that you have three VLANs. In normal networking theory it’s normal that broadcast initiated on host inside one VLAN will get to all host inside that VLAN but it will not get across to other VLAN. Typically the broadcast domain border is router or a Layer’s 3 switch VLAN interface. Although this is normal for most of broadcast traffic there needs to be a way to forward some kinds of broadcast traffic across that border. Why? Here’s a simple example. If you use DHCP, and you are, you will probably have hosts in different VLANs and all of them need to get the IP address from DHCP. If Forwarding UDP broadcast traffic didn’t exist it will be needed to have one DHCP server on every VLAN. Remember that DHCP works using broadcast traffic in some of the steps.

Simple DHCP address leasing:

Host that connects on the network will in the first step send broadcast DHCP discover message in order to find where the server is or if the server actually exist. After the HDCP replies with unicast DHCP offer host will one again use broadcast to send DHCP request to server. Server will then acknowledge the IP address leasing with unicast ACK message and that’s it.

Forwarding UDP broadcast traffic

All methods to mitigate IPv6 security issues
Real life security intro

In the process of configuring our corporate network test segment for IPv6, there was a direct demand to pay particular attention to security. It was my role to go trough all materials I could get to learn more about IPv6 security.

It was my role to go trough all materials I could get to learn more about IPv6 security. In that process, first stop was my favourite packetpushers podcast. They published more that 200 podcast till now and one of them was about IPv6 security that I needed. In that security show from last year

They published more that 200 podcast till now and one of them was about IPv6 security that I needed. In that security show from last year Healthy Paranoia Show 4:IPv6 Security Smackdown! Mrs. Y with bunch of great hosts discussed IPv6 security. They speak about almost all stuff that exists today in securing IPv6 enabled networks. One of the guests was Mr. Eric Vyncke, Cisco Distinguished Consulting Engineer who wrote IPv6 Security book for CiscoPress. Later, I did see that this book was everything you need to learn IPv6 security.  Of course, it’s easy to get edge router to run IPv6 on

One of the guests was Mr. Eric Vyncke, Cisco Distinguished Consulting Engineer who wrote IPv6 Security book for CiscoPress. Later, I did see that this book was everything you need to learn IPv6 security.  Of course, it’s easy to get edge router to run IPv6 on

Later, I did see that this book was everything you need to learn IPv6 security.  Of course, it’s easy to get edge router to run IPv6 on Internet-facing interface, but my goal is to get IPv6 inside our LAN environment and that part is still tricky if you include all the stuff needed to be done (especially on firewall part of the story).

I searched for additional information and some examples on how to configure Cisco gear for IPv6. Specially helpful were IPv6 webinars from long followed Networking/Cisco genius Ivan Pepelnjak at his great site ipspace.net (one of my homepage tabs). Here the guest is again Eric Vyncke.

After I gathered the knowledge out of those resources, I was ready to deploy IPv6 on my test segments and make it secure. Here are just a few rows about every one of IPv6 first-hop security features that are available on Cisco equipment. Just for the info, not all the equipment has all the features. Some of them came out

Here are just a few rows about every one of IPv6 first-hop security features that are available on Cisco equipment. Just for the info, not all the equipment has all the features. Some of them came out

Just for the info, not all the equipment has all the features. Some of them came out a few months ago so older switches and routers may not have all of these implemented. Sometimes you will be limited by the license to. I need to mention that other vendor’s equipment also supports most features mentioned below. For

I need to mention that other vendor’s equipment also supports most features mentioned below. For now it seems that Cisco invested the most effort and gathered the best team of engineers to add all possible features for IPv6 first-hop security inside IOS.

Let’s go with the list:

Intro

Multipath TCP is an extension of TCP that will soon be standardized by IETF. It is a succesful attempt to resolve major TCP shortcomings emerged from the change in the way we use our devices to communicate. There’s particularly the change in the way our new devices like iPhones and laptops are talking across network. All the devices like the networks are becoming multipath. Networks redundancy and devices multiple 3G and wireless connections made that possible.

Almost all today’s web applications are using TCP to communicate. This is due to TCP virtue of reliable packet delivery and ability to adapt to variable network throughput conditions. Multipath TCP is created so that it is backwards compatible with standard TCP. In that way it’s possible for today’s applications to use Multipath TCP without any changes. They think that they are using normal TCP.

Basics

We know that TCP is single path. It means that there can be only one path between two devices that have TCP session open. That path is sealed as a communication session defined by source and destination IP address of communicating end devices. If some device wants to switch the communication from 3G to wireless as it happens on smartphones when they come in range of known WiFi connection, TCP session is disconnected and new one is created over WiFi. Using multiple paths/subsessions inside one TCP communication MPTCP will enable that new WiFi connection makes new subsession inside established MPTCP connection without braking TCP that’s already in place across 3G. Basically more different paths that are available will be represented by more subsessions inside one MPTCP connection. Device connected to 3G will expand the connection to WiFi and then will use algorithm to decide if it will use 3G and WiFi in the same time or it will stop using 3G and put all the traffic to cheaper and faster WiFi.

TCP single path property is TCP’s fundamental problem

In datacenter environment there is a tricky situation where two servers are talking to each other using TCP to communicate and that TCP session is created across random path between servers and switches in the datacenter. If there are more paths of course. If there are (and there are!) another two servers talking in the same time, it will possibly happen that this second TCP session will be established using partially the same path as the first TCP session. In that situation there will be a collision that will reduce the throughput for both sessions. There is actually no way to control this phenomenon in TCP world. As in our datacenter example the same thing works for every multipath environment so it it true for example for the Internet.

Answer is MPTCP!

Multipath TCP – MPTCP is better as TCP in that enables the use of multiple paths inside a single transport connection. It meets the goal to work well at any place where “normal” TCP would work.