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 ...
- 1,095
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 ...
- 50.7k
17
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 ...
- 389
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....
- 854
11
votes
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, ...
- 36.3k
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 ...
- 4,305
9
votes
Accepted
Can't connect ssh via wireless interface but t works using eth0
I had the same debug3: set_sock_tos: set socket 3 IP_TOS 0x10 trace that you mention and turns out that, for my specific case, I solved it with this answer, which was related to how my router managed ...
- 237
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 ...
- 116k
7
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 ...
- 142
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 ...
- 5,222
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 ...
- 248k
7
votes
Subnet mask for 192.168.1.7/30
With 192.168.1.7 255.255.255.252, the addresses range from 192.168.1.4 - 192.168.1.7.
192.168.1.4 is the network address.
192.168.1.7 is the broadcast address.
You cannot apply either of those 2 ...
- 224
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 ...
- 69.1k
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 ...
- 1,306
5
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, ...
- 51
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
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 ...
- 36.8k
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 ...
- 7,982
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/...
- 132k
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
Accepted
simple routing don't work under debian jessie
As you don't mention you added a route on the third system, I'm guessing the problem is that the third system doesn't know how to route return packets to 172.28.11.0/24. So you need to add a route ...
- 3,924
4
votes
Accepted
DHCP renew fail - internet drops every 2 hours
Looks like your ISP network admin has a broken config on DHCP. Standard setup for DHCP client is to call in when lease is half over to renew, and to keep trying until renewal takes place. The log ...
- 870
4
votes
How to make a linux VM working as a router
You are on the right track with your firewall rules. I do things the "old fashioned" way - write a script, put it in /etc and call it from /etc/rc.local. However you like to do it, here's what works ...
- 1,498
4
votes
Accepted
What is the purpose of multiple ethernet ports on my modem?
The ethernet ports are for connecting multiple devices within your LOCAL network so they can communicate with each other. The modem, assumingly, from your ISP provides ROUTING functions to the ISP ...
- 870
4
votes
Accepted
Which DNS Server should I point at?
You should definitely use ISP as the first DNS entry, as that lets you take advantage of local / national caches.
Second entry should probably be ISP, but if both fail at the same time then that's ...
- 32.9k
4
votes
Accepted
Can Centos be configured to route private vlans?
You want 802.1q tunneling, or QinQ. See this:
http://www.microhowto.info/howto/configure_an_ethernet_interface_as_a_qinq_vlan_trunk.html
ip link add link eth0 eth0.100 type vlan proto 802.1ad id ...
- 56
4
votes
Need help choosing a router and/or wireless AP for a 15-40 person office?
The smart solution would be to engage a local company with specific expertise in this area. The last thing you probably want is to spend time and money on a solution that doesn't work. There's no ...
- 111k
4
votes
How can I duplicate incoming DNS packets and send them to a different nameserver with iptables?
The documentation says
The TEE target will clone a packet and redirect this clone to another machine on the local network segment. In other words, the nexthop must be the target, or you will have ...
- 3,168
4
votes
VLAN help (HP Switch)
First you should know that HP and Cisco use the term "trunk" differently. What HP calls a trunk, Cisco calls an Etherchannel (port aggregation).
I'll use the term in the Cisco sense (VLAN trunk) ...
- 2,179
Only top scored, non community-wiki answers of a minimum length are eligible