Networking – The Blog of Nitin J Mutkawoa, AKA @TheTunnelix

Category: Networking

35 commands to understand Firewalld in RHEL7 environment

10/10/2019 Nitin J Mutkawoa Add Comment

Firewalld provides a dynamically managed firewall with support for network/firewall zones that define the trust level of network connections or interfaces. It has support for IPv4, IPv6 firewall settings, ethernet bridges, and IP sets. There is a separation of runtime and permanent configuration options. It also provides an interface for services or applications to add firewall rules directly. – Firewalld.org

IPtables VS Firewalld

In RHEL6, we had IPtables. Now, in RHEL7, the firewall mechanism or say, the firewall daemon changed to Firewalld. Both serve the same purpose, i.e; packet filtering using the Netfilter module inbuilt in the Linux kernel. However, it is important to know why the Firewalld took over the IPtables. In Firewalld, you can change settings dynamically whilst being on production compared to IPtables which needs to flush out the entire rules set once a change has been made. Another difference is that during the installation of firewalld, you have support for both IPv4 and IPv6 compared to IPtables, you will have to install Ip6tables for IPv6 support. For those who are not acquainted with IPv6, please check out the article on “Diving into the basics of IPv6“. To briefly describe Firewalld, it is a set of services and daemons that manage the Netfilter in the Linux kernel. Finally, it is important to understand that both RHEL6 and RHEL7 used the IPtables (commands) to talk to the Netfilter.

Zones concept in Firewalld

One of the important concepts in firewalld is ‘zones’. Zones are groups of rules which is managed by the firewalld. Zones are based on the level of trust a user has on the interface and traffic within a network. Zones are even defined from least trusted to most trusted. These are the types of zones:

Drop zones: This is where incoming connections are dropped without any messages.
Block zones: Same as block zone but the only difference is that it gives an ICMP reply.
Public zones: It is an untrusted zone, but may allow connections based on case to case basis.
External zones: It is used when your firewall is also a gateway or simply, configuration for NAT.
Internal zones: This is the other side of the gateway or simply the firewall configurations used inside your own network, usually in a private network.
Demilitarized zones: Demilitarized zones or say DMZ, is where only certain incoming connections are allowed.
Work zones: There is a trust in the majority of hosts on the network which makes it possible to allow more services.
Home zones: The trust here is more and more acceptable and much more restrictions are removed.
Trusted: Here, there is absolute trust. Note that this should be used carefully.

VIEW information on your firewall

1. You can check if your firewall is running from either of the following commands:

systemctl status firewalld

firewalld-cmd --state

2. Like we said earlier, we can also check in which zone is the interface card configured:

firewalld-cmd --get-default-zone

3. Now, to check which interface card is in which zone, simply do the following. As you can see below, both interface cards enp0s3 and enp0s8 is in the active zone:

firewalld-cmd --get-active-zone

4. To check which rules are in the zones:

firewalld-cmd --list-all

5. If you want to get all the existing zones, simply do the following:

firewalld-cmd --get-zones

6. To list all existing rules within each zone, use the following:

Currently, you will also know which zones are your interfaces.

firewalld-cmd --list-all

7. But, you can still list the rules for a specific zone, say, the ‘home’ zone.

firewall-cmd --zone=home --list-all

8. For more details of all zones:firewall-cmd –list-all-zones

9. We have also seen, for example, in part 4 that firewall-zone –get-active-zone also shows us the services associated with the zone. But, we can also see a list of services with the firewall-zone command:

firewall-cmd --get-services

The services are just XML file located in /usr/lib/firewalld/services

Change information on the Firewall

10. Let’s say you want to move one interface from one zone to another zone. In my case, I want to move enp0s3 from the public to the home zone.

firewall-cmd --zone=home --change-interface=enp0s3

You can verify same using firewall-cmd –list-all-zones

11. However, another way to made verifications can be done using the command:

firewall-cmd --get-active-zones

12. Please note that restarting the service firewalld will result in loss of the change carried out. To ensure it is effective even after a restart of the service, go on the configuration on the network card which is /etc/sysconfig/network-scripts/ifcfg-enp0s3 and add the following line to it.

ZONE=home

13. Also, note that you can always change the default zone from public to home directly with the command:

firewall-cmd --set-default-zone=home

14. To add a specific service to a zone, for example, adding https to the zone public.

firewall-cmd --zone=public --add-service=https

15. Please note that this is only temporarily and after a restart of the service, the https will not be anymore in the home zone. To make it permanent:

firewall-cmd --permanent --zone=public --add-service=https

Always test your change with a firewall-cmd –reload

16. Most of the time, if you are running your own custom application, let’s say it is running on port 8080 and the services are not seen using firewall-cmd get-services, you can still add it to a zone by mentioning the port.

firewall-cmd --permanent --zone=public --add-port=8080/tcp

After adding the port, you must reload it to view the change.

More crazy Firewalld rules

17. You can also specify a range, for example, from 8000 to 8080 using the command:

firewall-cmd --permanent --zone=public --add-port=8000-8080/tcp

18. More interesting if you want to allow a specific IP Address for a specific zone, you can use the –add-source parameter:

firewall-cmd --permanent --zone=public --add-source=10.0.3.16/24

19. We can also block a specific IP Address from a zone. Let’s say we want to block IP 10.10.10.10/24 from the zone public. For that, we have to use the parameter –add-rich-rule.

firewall-cmd --permanent --zone=public --add-rich-rule='rule family="ipv4" source address="10.10.10.10/24" reject'

20. You might also want a particular service to be allowed from a particular IP Address. Let’s say we want to allow IP 10.10.10.5 for the zone public and only for the FTP service. In this example below, limit value=”2/m” means to limit 2 connections per minute.

[[email protected] services]# firewall-cmd --permanent --zone=public --add-rich-rule='rule family="ipv4" source address="10.10.10.5/24" service name="ftp" log prefix="tftp" level="info" limit value="2/m" accept'

21. Let’s say you want to know which zone is a specific interface. You can use the following command:

firewall-cmd --get-zone-of-interface=enp0s3

22. You can also find how many particular interfaces are in a particular zone:

firewall-cmd --zone=public --list-interfaces

23. To stop all communications, let’s say during an attack, you can fire this command:

firewall-cmd --panic-on

24. You can also stop the panic using the following command:

firewall-cmd --panic-off

25. You can also check if you are in a query panic using the following command:

firewall-cmd --query-panic

NAT, Port Forwarding and Masquerading

Network Address Translation (NAT) means to use a strategy to hide an IP address space into another IP address by modifying the network address information in the IP header. The packets in the IP header will transit through a routing device.

Port Address Translation (PAT) sometimes called Port forwarding works the same fashion except that it works on port level. You can forward port 22 on from your IP address to port 8000 to your internal web server.

The word Masquerading itself means to use something fake. NAT masquerading is another strategy to allow a device that does not have an IP address to communicate with other computers on the internet. IP Masquerading means to set up an IP gateway for a device.

26. To check if masquerading is on or off, you can use the following command:

firewall-cmd --query-masquerade

27. Or say you want to query a particular zone if masquerade is on or off, simply use the –zone parameter:

firewall-cmd --zone=public --query-masquerade

28. To enable masquerade for the zone public

firewall-cmd --zone=public --add-masquerade

29. Before performing a port forwarding, we need to enable the masquerading:

firewall-cmd --permanent --zone=public --add-rich-rule='rule family="ipv4" source address="10.10.10.5/24" masquerade'

30. Now, let’s say we want to forward all SSH traffic which is on port 22 to port 8000. This can be achieved using the following command:

firewall-cmd --permanent --zone=public --add-forward-port=port=22:proto=tcp:toport=8000

31. Since we did not define the IP address, it will redirect to localhost. Otherwise, you can also add an IP address:

firewall-cmd --permanent --zone=public --add-forward-port=port=22:proto=tcp:toport=8000:toaddr=10.0.2.16

32. You can also query it by using the parameter –query-forward-port:

firewall-cmd --permanent --zone=public --query-forward-port=port=22:proto=tcp:toport=8000:toaddr=10.0.2.16

Other stuff in Firewalld

33. You can also use firewalld on the graphic user interface. This can be done by installing the package firewall-config. The following command can be used:

yum install firewall firewalld-config

34. There are other ways to check if firewalld is running:

systemctl status firewalld

firewall-cmd --state

35. To active debug mode on firewalld logs enter the following parameter in the /etc/sysconfig/firewalld

FIREWALLD_ARGS='--debug'

After setting the parameter, the service need to be restarted.

If you want to get to the Ninja level using firewalld, please refer to this blog article by certdepot.net

Linux System, Networking, Security cybersecurity, DevOps, firewall, linux, security

Diving into the basics of IPv6

04/21/2019 Nitin J Mutkawoa Add Comment

The Internet is growing. In case you are not on IPv6, for sure one day, you might need to migrate from IPv4 to IPv6. Now what kind of methodology you would apply whether a dual stack or a direct changeover depends upon a rigid observation and analysis of the network infrastructure. But, it should no more be taken as a complexity. Since a few years, many companies, government bodies, ISPs, and others are moving towards IPv6. Some are adopting dual stack. IPv6 can be said to be version 2 of the Internet. In this blog post, I will make my best to shed some basics and simple way to understand the features and benefits when using IPv6. I will also contrast it with IPv4. For research purpose, I have perused several books and blogs over the Internet and, same are referenced below. One of the challenges in Africa is to enable the smooth transition to IPv6. Whilst others are doing dual stack, others have successfully migrated the whole network infrastructure to IPv6. IPv4 has been created in the early ’80s. The Internet growth which is so huge and it will definitely need to move ahead with modern technology IPv6 running at its core. I had always admired one of the modern futurist physicist, Dr. Michio Kaku who said that “In the future, the Internet might become a brain“.

So why do we really need IPv6?

Besides, from the growth of the Internet and the scarcity of IPv4 addresses, we all knew that in IPv4, the network has been divided into two parts which are the Private IPs and the Public IPs allocation. And, those two segments which are Interconnected required NAT configuration. This breaks the contiguous of the Internet. Another reason is that there is no security in IPv4 at its core. Of course, there are other strategies to secure an IPv4 network. When it comes to data prioritization, it cannot be done at the core of IPv4 which means that there is not much of Quality of Service (QoS). In IPv4, we can configure or assigned an IP to a device or simply use an address configuration mechanism such as DHCP. But, the moment DHCP is down, we land into a problem. Here is the catch, this means that there is no way to make a device to be assigned a globally unique address. So, that’s why we need IPv6. Well, wait… What happened to IPv5 ? and what about IPv1, IPv2, and IPv3?

What happened to IPv1, IPv2, IPv3, and IPv5?

Have a look at the diagram below which makes it pretty easy to understand:

So, IPv0, IPv1, IPv2, and IPv3 were used in the development testing phase. Ipv5 was used while doing the Stream experimentation of the Internet.

Features of IPv6

There is no backward compatibility when using IPv6, but, the basic functions remain the same, and the features have been changed completely. Since IPv4 is a 32-bit address and IPv6 is a 128-bit address, just imagine how much bigger it is. When compared to an IPv4 address bit, IPv6 has four times more bits. We can say that there are more than 1500 IP addresses per square meter on earth.

Another feature of the IPv6 is about the header which is twice the size of IPv4.

In IPv6, there is also end-to-end connectivity which means that NAT is not required for the continuity of the Internet. Every host can reach another host over the Internet.

Other features are “auto-configuration” which can be either stateful or stateless. Stateless is a mechanism that does not require any intermediate support in the form of DHCP for IP assignment whereas Stateful serves IP addresses from a pool. Also to take into consideration is “faster routing”. In IPv6, the routing information is stored in the first part of the header which makes routing decisions faster by the router. Another feature is IPSec (IP Security). It creates an end-to-end tunnel between the source and the target though it is optional. “No Broadcast” is another feature within IPv6. Using an IPv4 network, you will notice during the IP Address configuration, the clients need to broadcast to the DHCP. In IPv6, the client doesn’t need to broadcast and instead will multicast to communicate with machines over the network. It is important to understand the difference between ‘broadcast’ (one-to-all) and ‘multicast'(one-to-many). In broadcast, clients will send messages to all hosts on the network, whereas in multicast, messages are sent to a group of stations. This allows the building of distribution networks where group management is required. IPv6 does not limits itself to multicast but also bring the ‘unicast’ (one-to-one) feature. This is used especially between routers which need to communicate to a specific router. However, if you have several routers nearby and you can choose any routers for communication, let’s say for a CDN purpose, we can use the anycast method to process efficiency packet routing.

Photo Credits: techiemaster.wordpress.com

Reading IPv6 addressing

Now, that you have grasped the basic concepts of IPv6 and why we need it, let’s see how to read IPv6. An IPv6 address is made up of 128-bits divided into 16-bits blocks. Each block is then converted into 4-digits hexadecimal numbers separated by colon symbol. For example, this is an IPv6 address in binary:

0010011000000110 0100011100000000 0000000000110000 0000000000000000 0000000000000000 0000000000000000 0110100000010010 0010100001100000

Since we have three series of zeros, it can be escaped between the two colons symbols. Leading zeros in the third block will result in 30. In case, you had one block of zeros, use one zero in the hexadecimal IP address. When converted to hexadecimal it is:

2606:4700:30::6812:2860

Let’s get into more details. There are two rules when reading an IPv6 address.

Rule1: Leading zeros should be discarded. As we can see in the 3rd block of the IPv6 address above i.e; 0000000000110000 when converted it is written as 30, because it can be read as 110000. Here is a video on how to convert Binary to Hexadecimal.

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Rule2: If two or more blocks contain consecutive zeros, omit them all and replace by double colons signs. Example the three blocks of zeros in purple above have been replaced as “::“, However, if there is a single block of zero, use 0 in the IPv6 address.

Assignment of IPv6 address

Similar to IPv4, we need to understand how to identify the number of networks and hosts in IPv6. Let’s take an example from a generic unicast address which uses 64-bits as network ID and 64-bits as hosts ID. Please note from the picture below the 64-bits in the network has been shared in three distinctive fields in the IPv6 packet structure.

At this stage, it should be clear how a generic unicast address has been designed. Now, another important point is the IPv6 address scope. A scope is a region where an IPv6 address can be defined as a unique identifier of a network interface. As we can see below, there are three scopes, Global Unicast Address, Unique Local, and Link Local.

Photo Credits: steves-internet-guide.com

The Global Unicast Address is routed and is reachable across the Internet. Also. the prefix for global routing prefix in IPv6 has been assigned by the Internet Assigned Number Authority – IANA, so that by only looking at the prefix of an IPv6 address, you can determine if its global or not. In the picture below, you can see the first 3 bits within the global prefix. Remember, that this is unique globally.

Then, comes the Site level aggregator – SLA which is the subnet ID assigned to the customer by the service provider. This follows by the LAN id that is used by the customer and is free to manipulate. This address is globally unique.

Let’s take a look at a Unique Local Unicast Address. It looks like private IP addresses and is used for local communication intersite usually in a LAN and for VPN purpose. It is not routable on the Internet.

The last one is the link local unicast address. This is used for communication between two IPv6 devices on the same link. By default, it is automatically assigned by the device as soon as IPv6 is enabled, and it is not routable. These types of IP addresses are identified by the first 10-bits of the address, i.e; FE80.

In this blog post, I took an example from only Unicast addresses. Remember, there are also Multicast and Anycast address ranges. Let’s now create some servers and perform some IPv6 configurations.

Goodbye IPv4 and, say Hello to IPv6

I created a CentOS7 machine on my VirtualBox. As you can see, the interface card enp0s8 have the IP Address 192.168.100.9 as well as fe80::9ef3:b9d3:8b87:4940. Remember, the fe80 is the Link Local Address.

You can also see the connection using the following command:

To create a connection using nmcli use the following command and check back the connection. You will notice that the connection has been created without any device attached to it.

I am now modifying ipv6-tunnelix and attached it to enp0s9. I will also assign it to an IPv6 address. (For learning and testing purpose, this IPv6 address has not been assigned to me, it’s that of Facebook’s public IPv6)

As you can see, the address has been assigned. But remember, same as you can assign a public IPv4 address on a virtual machine, you will need to route it for connectivity. In this example, I took an example of Facebook public IP Address.

Are your blog’s IPv6 ready?

In 2016, during migration on Cloudflare, tunnelix.com became dual stack i.e; both compatible for IPv4 and IPv6. You can test any website for IPv6 support at this link.

https://ipv6-test.com

Certifications

Getting certified on IPv6 is really interesting as it can demonstrate comprehensibility. You can participate in free IPv6 training and get certified from Hurricane Electric. It is important to read the IPv6 primer.

There is also a service from Hurricane Electric, called Tunnel Broker which can facilitate you for creating a tunnel from your IPv4 static IP address to free IPv6 tunnels. In future blog posts on IPv6, I will get into more details about it. If you like the article, please comment, and share.

Sources:

Networking, Security centos, CloudComputing, IPv6, linux, VirtualBox

cyberstorm.mu VideoStream #2 : Modem Insecurity in Mauritius

10/25/2017 Nitin J Mutkawoa Add Comment

Some days back, the cyberstorm.mu (Name rebranded due to trademark issue) team made our first video stream on Youtube about Modem Insecurity in Mauritius. We received several feedbacks from the public, friends and local media about the issue raised. Upon further research, I noticed that there are several countries including Vietnam, China amongst others are in the same problematic situation as they are using the same Huawei modem. More and more vulnerabilities are now being faced by the end users. Users aware of the issue can mitigate it from their side whilst others are still in the dark.

On Friday, the 20th of October 2017, another video stream was carried out by the cyberstorm.mu alongside other friends and professionals. We started with a short introduction from everybody in the videostream.

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We had Billal, Codarren, Edriss, Irshaad, Logan, Kifah, Selven, Rahul, Yash and myself (Nitin) participating in the video stream. You can view the VideoStream here:

Our agenda was as follows:

An introduction from participants
Huawei’s acceptance of upgrading Dnsmasq
Other discoveries in the Huawei modem
The implication of Krack attack
Understanding the mitigation techniques on Krack attack
Everyone’s perspective about the vulnerabilities on the Huawei modem

Other sources talking about cyberstorm.mu‘s insecurity detection on the Huawei modem

Local media – Securing your modem – French article

MeetUps and Presentations, Networking, Security cyberstorm.mu, Internet, security

cyberstorm.mu VideoStream #1 : Modem Insecurity in Mauritius

10/17/2017 Nitin J Mutkawoa Add Comment

On Tuesday the 17th of October 2017, the cyberstorm.mu team had a public podcast on Modem Insecurity in Mauritius. Fifteen minutes after the start of the broadcast, there were already about 30 views from the public. We had over Keshav Purdassea, a student in cybersecurity as a guest to ask questions. We also had people asking questions on the Facebook cyberstorm.mu public group.

Logan from cyberstorm.mu made a smart introduction during the podcast about its goal which is informing the public about the vulnerabilities found in Huawei Modem.

Codarren from cyberstorm.mu laid emphasis on several interesting points such as the state of Dnsmasq. He also gave some interesting hints to launch commands on the router which is not similar like a usual Linux Box. He explained how all processes are running as root including Dnsmasq. Codarren recently had a conversation with engineers from Huawei and it’s quite obvious that Dnsmasq is also doing DNS. It was recommended to run dnsmasq as a non-root user which is one of the best practice in any Linux Box. Someone can craft a DNS packet and run this on the modem with the intention to control it remotely. This security risk needs to be reviewed again.

In addition, I made a brief introduction to the preliminary precaution that can be taken to minimize impacts such as deactivating Telnet or even SSH on the router. We also noticed how it’s possible to download the configuration file and decrypt it. All passwords can be seen clearly on the configuration files. Here are the steps to be followed to decrypt it :

1. Use the following command to decrypt it :

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[[email protected] ~]# ./aescrypt2_huawei 1 hw_ctree.xml decode.xml

2. To re-encode use the following command:

[[email protected] ~]# ./aescrypt2_huawei 0 decode.xml hw_ctree.xml

3. At line 1022, You can find the web interface password

1022 <X_HW_WebUserInfoInstance InstanceID="2" UserName="telecomadmin" Password="402931e04c03e24d360477a9f90b9eb15777e154360f06228be15c37679016ef" UserLevel="0" Enable="1" ModifyPass wordFlag="0" PassMode="2"/>

We also had Yash who made a sensitive point regarding as to whether the patch was supposed to come from Mauritius Telecom or Huawei. After some research, we noticed that there was no patch from Huawei itself.

The whole team of cyberstorm.mu and I invite you to join our Facebook group and Twitter to keep in touch for our oncoming Live podcasts, Hackathons, Public events, etc..

Other bloggers on the Podcast:

Billal Abdel Hassan – Linux passionate – Modem insecurity
Irshaad Abdool – Vulnerabilities on MT FTTH routers

MeetUps and Presentations, Networking, Security cyberstorm.mu, security

Tunnelix.com is now IPv6 ready! Are you?

07/17/2016 Nitin J Mutkawoa Add Comment

Validated by IPV6-test.com, Tunnelix.com is now IPV6 ready. Woohoo.. I now have the IPv6 validation button 🙂 Can you spot it?

So, what is exactly IPV6-test.com? IPv6-test.com is a free service that checks your IPv6 and IPv4 connectivity and speed. Diagnose connection problems, discover which address(es) you are currently using to browse the Internet, and what is your browser’s protocol of choice when both v6 and v4 are available.

How I got an IPv6 address?

If you are running a low-cost budget blog, I would recommend you to try out Cloudflare to have made maximum use of the free IPV6 address that you can activate on the network tab. The IPv6 compatibility option is not activated by default.

Cloudflare provide both free and paid service for CDN service, security, DDOS protection etc… However, the IPv6 address is a free one.

Why you might need to start moving towards IPv6 ?

Loganaden Velvindron of cyberstorm.mu recently shed some light in his Medium blog after attending the National Innovation Framework in Mauritius “The other issue that I think is strongly lacking are the remaining IPv4 resources left in our region to be able to make Internet of things a reality. There are currently 26.4 million of IPv4 addresses left, and it keeps shrinking at a frightening rate.” The world is running out of IPv4 addresses. I think we need to move on quickly on the IPv6 world because of Internet of Things (IoT) will depend on IPv6.

What is an IPv6? What are the parts of an IPv6 ?

Lets now get on the technical parts. As you should know already IPv4 use 32 bits infrastructure whilst an IPv6 use 128-bits which makes an IPv6 a lot more longer. Here is an idea of a representation of an IPv6 adress.

As you can see IPv6 address is composed of 8 segments of 4 hexadecimal strings. A simple math is by multiplying 8×4=32 then 32×4= 128 bits. When representing IPv6 addresses, zeroes are compressed and leading zeroes are further compressed by representing it with “: :” . See picture above.

The internet might run out of room

Since 2012, Vint Cerf, Chief Internet Evangelist at Google, and a founding father of the Internet, discussed the next version of the Internet, IPv6, and why we need it. Just as phones use a system of phone numbers in order to place calls, every Internet-connected device gets a unique number known as an “IP address” that connects it to the global online network. Watch out the video

Networking, Security IPv6, security

Category: Networking

How To Convert Binary to Hexadecimal