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#1 2019-01-11 09:30:14

bugsmanagement
Member
Registered: 2017-04-21
Posts: 175

Understanding the fundementals of Network Routing.

Hello everyone,

For the past few days, I've been experimenting with routing through Virtual Machines organize in different bridges or on the same bridge with a firewall/router sitting in the middle. Using wireshark and looking up information I could find on the web (eg. https://support.microsoft.com/en-us/hel … ng-basics), I'm trying to understand how routing works.

Apologize for my crude diagrams.

Network topology 1:

vm1 (10.0.1.2/24)+------------>bridge1+---------+
                                                |
                                                |
                                                |
                                                v
                                         (10.0.1.1/24)
                                         Firewall Router
                                         (10.0.2.1/24)
                                                ^
                                                |
                                                |
                                                |
 vm2 (10.0.2.2/24)+----------->bridge2+---------+

Network topology 2:

vm1 (10.0.1.2/24)++
                  |
                  |
                  |
                  |
                  v
               bridge3+----------------> Firewall Router
                  ^                      (10.0.1.1/16)
                  |
                  |
                  |
                  |
 vm2 (10.0.2.2/24)+-

My questions:

My understanding so far, please correct me when necessary, that networks that are unreachable in one's subnet (or local network), then the packets are forwarded, if such route is defined in the routing table (eg. default route). That's done at Layer 3 (previously assumed Layer 2 but was corrected here https://searchnetworking.techtarget.com/definition/OSI). Layer 3 is ethernet frames? That's done via mac addresses? Then the remote then decides how to route packets.

For topology 2, is it possible to use mac addresses in the routing table instead of IP addresses? Why use IP addresses anyway? How does the OS determine how to route packets based on IP address, through ARP (eg, using ARP to get mac address)? Vm2 ignores ICMP packets from vm1 though responds to them if they come from the firewall mac address? What field/bit in the Layer 3 (Ethernet Frame), "hey I'm routing this packet?", that changes this behavior?

I believe if understand topology 2 routing behavior, I'll then understand topology 1 routing behavior.

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#2 2019-01-11 12:57:20

Lone_Wolf
Member
From: Netherlands, Europe
Registered: 2005-10-04
Posts: 6,680

Re: Understanding the fundementals of Network Routing.

you're confusing yourself and mixing up things.


There are 4 basic networking devices : hub, bridge, switch and router.

network hub
network bridge
network switch
differences-between-a-switch-and-a-bridge
router

Read all 5 links, then try to anwer one of your own questions :

For topology 2, is it possible to use mac addresses in the routing table instead of IP addresses? Why use IP addresses anyway?

NB : you may need to read the network introduction section of that course also

Edit: changed to  another question

Last edited by Lone_Wolf (2019-01-11 13:17:13)


Multi-init booting with apg Openrc and systemd coexisting
Automounting : not needed, i prefer pmount
Aur helpers : makepkg + my own local repo === rarely need them

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#3 2019-01-11 13:30:45

bugsmanagement
Member
Registered: 2017-04-21
Posts: 175

Re: Understanding the fundementals of Network Routing.

Lone_Wolf wrote:

Do network bridges belong in a routing diagram ?

Probably not but I'd be happy to take donations to purchase proper network gear to learn network topology and routing?

Is there a difference between this https://en.wikipedia.org/wiki/Bridging_(networking)? What term what you use instead?

I still need to read up more on network switches.

For complete disclosure, I'm am ignorant in some aspects, well most, but doing a diagram was something I thought would better explain what I was doing. The goal for me, is better understand wireshark traffic dumps. It's that curiosity that's driving me to learn more.

For additional context, I was running tcpdump on both VMs

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#4 2019-01-11 13:47:22

Lone_Wolf
Member
From: Netherlands, Europe
Registered: 2005-10-04
Posts: 6,680

Re: Understanding the fundementals of Network Routing.

bugsmanagement wrote:

Is there a difference between this https://en.wikipedia.org/wiki/Bridging_(networking)? What term what you use instead?

Both describe the same device, but the wikipedia article focuses on technical details while the geek university article focuses on functionality.

bugsmanagement wrote:

I still need to read up more on network switches.

For complete disclosure, I'm am ignorant in some aspects, well most, but doing a diagram was something I thought would better explain what I was doing. The goal for me, is better understand wireshark traffic dumps. It's that curiosity that's driving me to learn more.

For additional context, I was running tcpdump on both VMs

Diagrams can be ve very useful, but yours don't show them correctly.
MS Visio is one of the best for creating network diagrams, but afaik that doesn't work under linux.
I've had reasonable results with dia


Multi-init booting with apg Openrc and systemd coexisting
Automounting : not needed, i prefer pmount
Aur helpers : makepkg + my own local repo === rarely need them

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#5 2019-01-11 13:53:33

progandy
Member
Registered: 2012-05-17
Posts: 3,306

Re: Understanding the fundementals of Network Routing.

bugsmanagement wrote:
Lone_Wolf wrote:

Do network bridges belong in a routing diagram ?

Probably not but I'd be happy to take donations to purchase proper network gear to learn network topology and routing?

You don't need special hardware, there are simulators available if a setup with only VMs (and e.g. Open vSwitch) is not sufficient.

http://www.brianlinkletter.com/open-sou … imulators/

Last edited by progandy (2019-01-11 13:57:11)


| alias CUTF='LANG=en_XX.UTF-8@POSIX ' |

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#6 2019-01-11 14:09:10

bugsmanagement
Member
Registered: 2017-04-21
Posts: 175

Re: Understanding the fundementals of Network Routing.

I am going to have use that site more often and read, how is their 'search'?

progandy wrote:

You don't need special hardware, there are simulators available if a setup with only VMs (and e.g. Open vSwitch) is not sufficient.

http://www.brianlinkletter.com/open-sou … imulators/

I really appreciate that, that would avoid me deploying full blown vms. Is theirthere UI  learning curve?

Lone_Wolf wrote:

[...]university article focuses on functionality.

I thought I was using it for that reason.

Last edited by bugsmanagement (2019-01-11 14:11:29)

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