vlan# interface

[Allanm]

Hi Folks,

I have an application which is getting binded to vlan0(virtual ip) interface even though its suppose to bind to the default interface.

The IP address of vlan interface is x.x.0.0.
It has the same ether address as the primary interface.

I have explored the configs for the app but no luck why its getting binded to that interface and not to the primary one.

What could be wrong here?

Thanks,
Allan.

[Matti_Kurkela · Accepted solution]

How can you even have interfaces like "vlan0" in HP-UX? Do you have some third-party networking software installed?

Which version of HP-UX are you running?

In HP-UX 11.31 native APA, VLANs would normally appear as high-numbered lan interfaces, e.g. lan5000 or above.

On the other hand, IP aliases (= multiple IPs for the same interface) would be named like lan0:1, lan0:2 etc.

Are you talking about incoming or outgoing connections?

Normally, outgoing connections are not bound into any particular interface by the application, so the OS is allowed to choose an appropriate source IP. The OS makes this choice by looking at the routing table to select the most direct route for delivering the connection to its destination, and choosing the source IP as appropriate for that route. If the same network entry has multiple applicable source IP addresses, the one that's listed first in the routing table is normally used.

If you haven't specified a netmask when configuring your interfaces or routes, a default netmask is chosen according to the old (pre-CIDR) class rules. For class A addresses (1-127.*.*.*), the default netmask is 255.0.0.0.

It is possible for the application to bind both incoming and outgoing connections to a particular local IP address, if that is desired. Normally, sockets listening for incoming connections are bound to a wildcard IP and a particular port: if a socket is bound to a specific local IP address, this behaviour is usually configurable, or somehow tied to the application's idea of the local hostname. Either way, this behaviour is application-specific: you might get a better answer by sending the question to the support services of your application.

If you want people on the forums to have any chance of analyzing this further, please show at least the outputs of "netstat -i" and "netstat -rnv" for analysis, if you're allowed to do that.

If disclosing that information to the Internet is not allowed, you'll have to find someone with the necessary knowledge (either within your organization or a consultant) who can sign an appropriate NDA and then be allowed to see the network parameters.

MK

[Allanm]

Thanks Matt.