45
votes
Accepted
What happens if two local systems download the same resource on same port?
A TCP connection (which underlies HTTP and many other protocols) is uniquely (at a given point in time) defined by 4 parameters:
The local IP
The local port
The remote IP
The remote port
Even if you ...
- 1,030
27
votes
Accepted
Do I really need a DB9-RJ45 adapter to connect to a Cisco router console, and if so, why?
While using a classical RJ45 jack, the connection on your Cisco router really is a RS232 serial connections.
This means that, independently from the physical connector, your PC need to speek the same ...
- 45.5k
18
votes
How does a router get its IP address assigned?
IANA is the organization responsible for global IP assignments. They assign "blocks" of IP addresses to Regional Internet Registries which are geographically based organizations responsible for ...
- 5,367
17
votes
Accepted
CentOS 6 router/firewall seems to be throttling throughput
So, the problem here turned out to be a hardware issue. Things were working fine a month ago, and one does not expect failed hardware to still "work" in a degraded mode, but that's what was happening....
- 844
16
votes
Bridging wlan0 to eth0
Bridge wlan and 4addr:
Bridging wlan0 is a pain. You normally cannot add it to a bridge interface (brctl returns "Operation not permitted"), and using VirtualBox "bridged" filter ...
- 379
14
votes
Accepted
Why is routing neither CPU nor memory intensive?
What part of a router's job takes up RAM? Precious little. Packets in, packets out. The network stacks of modern operating systems are very well-tuned, and all packet inspection and routing happen ...
- 109k
11
votes
What happens if two local systems download the same resource on same port?
The NAT table knows that the source port on each client is different, so it won't accidentally send the wrong packet to the wrong internal client. The NAT device also assigns different outbound ports, ...
- 35.9k
10
votes
How does a router get its IP address assigned?
(Here I'm talking about the customer edge router. The one which is on your LAN. In the ISP network, the router is usually/probably configured manually).
If you have a PPP-based connection (PPPoE, ...
- 1,643
9
votes
Accepted
How does DNSMasq integrate with my router?
DNSmasq does not need to communicate with your router. The DNSmasq service just took over the service of DNS and DHCP and your router does not have to provide that anymore. Since you have disabled the ...
- 4,205
8
votes
Accepted
ESXi 5.5 Isolate Network
This is almost nothing to do with being on an ESXi host - it's a routing issue - you just need two separate VLAN coming from your router, both of which have external routes out and no routing between ...
- 101k
7
votes
Accepted
Do I need a managed switch for my home network?
Your mixing things up a bit. Layer 2 switches and Layer 3 switches both function as network switches with the difference being that a Layer 3 switch has the capability of being able to perform routing ...
- 109k
7
votes
CentOS 6 router/firewall seems to be throttling throughput
What I would do here is revert the changes individually and run a speed test after each or revert all the changes. Benchmark an unmodified version of CentOS (baseline) and then apply each change ...
- 115k
7
votes
7
votes
Port forwarding test possible within LAN? Mikrotik Router
Mikrotik RouterOS based on the Linux kernel and has inherited most of the conceptions of networking.
So, I'll describe the setup of the port forwarding in the Mikrotik routers. And I'll try to ...
- 4,982
7
votes
Accepted
When to use routers and when to use layer 3 switches
As you already know, a layer 3 switch includes a basic router. If the device has the functionality you need, then it should be fine to use. For instance, a layer 3 switch generally won't do NAT or ...
- 241k
6
votes
Linux HTTPS Header inspection
Thanks to SNI, you can easily get the server name that data is being requested from, but the entirety of the rest of the conversation (including the rest of the URL) is (as designed) encrypted and ...
- 109k
6
votes
Accepted
What does the command "ip route" show
Your assumption is accurate:
10.255.114.0/23 is directly connected as it is in the same subnet as 10.255.115.18 (i.e. /23 is 10.255.114.0 to 10.255.115.255 ).
scope link means the packet is just ...
- 132
6
votes
Accepted
Seamless transition from internet to local network
Hairpint NAT (sometimes called NAT Reflection) is what you need here. Some routers will do this automagically (often the cheap consumer ones will), but others will not (Mikrotik will not, but is a ...
- 68.6k
6
votes
What happens if two local systems download the same resource on same port?
When you refer to NAT you are probably actually referring to NAPT.
Which changes the source port (at least if needed) in the NAT device.
As such the source port will change.
For example iptables ...
- 1,208
5
votes
Bridging wlan0 to eth0
4addr as described in other answers is certainly the best way when supported by the adapter/driver, but not all of them does. NAT might work for some things, but getting proper communication both ways ...
5
votes
Bridging wlan0 to eth0
Depends on how mean the AP is to you:
1) It might only want to see packets coming from you, with your known link layer address (and hence not of bridged packets)
2) It might actually be even smarter, ...
- 331
5
votes
Accepted
Is enabling https on a Cisco router a considerable security risk?
As an Information Assurance (IA) principle, the less unnecessary services running on a device, the lower the attack surface. To mitigate issues, proper configuration and patching levels are key. ...
- 1,313
5
votes
Different subnet mask on router and DHCP server
The subnet mask is mostly used to work out whether another IP address can be accessed on the local network, or if it needs to go through a router. Your workstations with the old /24 subnet mask will ...
- 7,983
5
votes
Accepted
NOIP Static IP address resetting with router
NOIP does not do what you want.
Some ways you might achieve what you want:
Purchase a VPN connection with a static IP at the other end
Purchase a static IP from your ISP
NOIP and other dynamic DNS ...
- 5,587
5
votes
I am setting up an internal AD Windows Server 2012 domain. The company's name is xyz there is already a external domain
Register and use a top-level domain name that you own. Do not use a domain name that is owned by another entity, not registered, or not a well-known top-level domain. Using a domain name that is owned ...
- 35k
5
votes
Accepted
IPv6 - How does my ISP know how to route traffic to my delegated subnet?
IPv6 to consumer networks/customers is usually provided by using DHCPv6-PD between the ISP router and the home router (CPE). The PD stands for Prefix Delegation and is an addition to the normal DHCPv6 ...
- 7,672
5
votes
Accepted
How to interpret Firewall logs?
Most of these are pretty obvious abbreviations of the names used for the fields/flags of the IPv4, TCP, and UDP headers.
https://en.wikipedia.org/wiki/IPv4#Header
https://en.wikipedia.org/wiki/...
- 130k
5
votes
What happens if two local systems download the same resource on same port?
The router doesn't use the same source port number that the laptops generate in its outgoing requests to the WAN, it generates its own unique source ports. The NAT table in the router converts laptop1:...
- 151
4
votes
Blocking WhatsApp and other IM traffic
Apply a filter using the official IP list: https://www.whatsapp.com/cidr.txt
Use QoS instead of blocking.
- 187
4
votes
What is strict, moderate and open NAT?
All of these NAT terms are used only in the gaming industry. If you ask a network engineer or security engineer about strict nat, they are not going to know what you are talking about.
In the real, ...
- 41
Only top scored, non community-wiki answers of a minimum length are eligible