tcpip

Multiple IP addresses per NIC

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Yes, it can be done in Windows: Go to the Control Panel > Network Connections Right click on the Local Area Connection (or whichever network connection you want to add the 2nd IP Address) and click Properties Click on Internet Protocol (TCP/IP) in the connection box and click properties Enter the first IP address in … Read more

What is the maximum number of TCP connections I can have in Windows Server 2008?

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You can go well beyond 65k connections; as you can have multiple connections per port (once accepted, the listener can connect to another client). One end or the other does have to have some difference, usually the client picks a random port. Windows is by default limited to a few more than 3000 of these … Read more

Tuning NFS client/server stack

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Just to clarify, you’re getting 50MB/sec with NFS over a single Gb ethernet connection? And the host server is running CentOS with VMware Server installed, which is in turn running the 7 VMs? Is there a particular reason you’ve gone with CentOS and VMware Server combined, rather than VMware ESXi which is a higher performance … Read more

Where is the documentation that states TCP and UDP source port should be over 1024 and random?

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You are probably looking for RFC 6056 – Recommendations for Transport-Protocol Port Randomization (“Best Current Practice”). Technically there is no requirement that the ephemeral port be >1024 or random (you could build a system that always initiates connections from port 12 because you like the number 12), it’s just not “normal” to do so (and … Read more

AWS flagged my subnet as invalid although it looks to be within the VPC CIDR block

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Nope, 10.8.0.0/24 doesn’t fall into 10.0.0.0/16. AWS is correct, sorry 🙂 In your 10.0.0.0/16 you can create subnets between 10.0.0.0/24 to 10.0.255.0/24, e.g. 10.0.8.0/24 would work. Let’s say we’ve got CIDR address 10.20.30.40 – that can fall for example into these subnets: 10.0.0.0/8 – /8 means only the first byte (10.) in the address is … Read more

Slash Notation IP – What is what?

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The /30 means all but two of the 32 bits are used to define the netmask. It also means you’ve got four IP addresses to play with. (But in reality, only two of which can be hosts) Your last octet of the netmask is (in binary) 11111100, which leaves the last two bits for you … Read more

What do all the settings in the Advanced TCP/IP Properties DNS Tab Mean?

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Here’s a shot: DNS server addresses, in order of use: This lists the name servers that your machine will contact for DNS resolution, in the order they will be contacted should one higher in the list be unreachable. Append primary and connection specific DNS suffixes When performing a name resolution request, this will append the … Read more

When IP aliasing how does the OS determine which IP address will be used as source for outbound TCP/IP connections?

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By default, on Linux, if an interface has multiple addresses that are on different subnets, traffic destined for the respective subnets will have the proper source IP. That is, if eth0 has two addresses 192.168.1.1/24 and 10.1.1.1/8, then traffic to anything on the 10.0.0.0 subnet will have source 10.1.1.1, and traffic to anything on the … Read more