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Top Forums UNIX for Advanced & Expert Users Very Challenging Question! Need help bad! Post 12827 by wizard on Monday 7th of January 2002 09:49:38 PM
Old 01-07-2002
Short answer:

The plumb argument to the ifconfig command is for dynamically activating a network interface without rebooting the system.

Long answer:

If you are configuring a network interface for the first time, you would first physically add the NIC to the machine and perform a reconfiguration boot. You would then add an IP/interface name in /etc/inet/hosts, and create a
/etc/hostname.<interface istance> file with the interface name in it. <interface names> above is built from the interface type and the instance number of that type.

For example:

On Sun Ultra boxes, the 10/100 interfaces are of type hme. If you are adding the first interface the file would be /etc/hostname.hme0. If you wanted the interface name to be myhostname, you would put the word myhostname in /etc/hostname.hme0 along with a corresponding IP/interface name entry in /etc/inet/hosts. You would then reboot to add the interface.

If you wanted to configure an interface without rebooting the machine (you would still have to add the NIC and perform a reconfiguration boot first), you can use

ifconfig hme0 plumb

(hme0 should be replaced with the proper interface name).
This will activate the interface and allow you to configure the IP, netmask, broadcast, etc. using ifconfig.

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CARP(4) 						   BSD Kernel Interfaces Manual 						   CARP(4)

carp -- Common Address Redundancy Protocol SYNOPSIS
pseudo-device carp [count] DESCRIPTION
The carp interface is a pseudo-device which implements and controls the CARP protocol. carp allows multiple hosts on the same local network to share a set of IP addresses. Its primary purpose is to ensure that these addresses are always available, but in some configurations carp can also provide load balancing functionality. A carp interface can be created at runtime using the ifconfig carpN create command. To use carp, the administrator needs to configure at minimum a common virtual host ID and virtual host IP address on each machine which is to take part in the virtual group. Additional parameters can also be set on a per-interface basis: advbase and advskew, which are used to con- trol how frequently the host sends advertisements when it is the master for a virtual host, and pass which is used to authenticate carp advertisements. Finally carpdev is used to specify which interface the carp device attaches to. If unspecified, the kernel attempts to set carpdev by looking for another interface with the same subnet. These configurations can be done using ifconfig(8), or through the SIOCSVH ioctl. Additionally, there are a number of global parameters which can be set using sysctl(8): net.inet.carp.allow Accept incoming carp packets. Enabled by default. net.inet.carp.preempt Allow virtual hosts to preempt each other. It is also used to failover carp interfaces as a group. When the option is enabled and one of the carp enabled physical interfaces goes down, advskew is changed to 240 on all carp interfaces. See also the first example. Disabled by default. net.inet.carp.log Log bad carp packets. Disabled by default. net.inet.carp.arpbalance Balance local traffic using ARP. Disabled by default. EXAMPLES
For firewalls and routers with multiple interfaces, it is desirable to failover all of the carp interfaces together, when one of the physical interfaces goes down. This is achieved by the preempt option. Enable it on both host A and B: # sysctl -w net.inet.carp.preempt=1 Assume that host A is the preferred master and 192.168.1.x/24 is configured on one physical interface and 192.168.2.y/24 on another. This is the setup for host A: # ifconfig carp0 create # ifconfig carp0 vhid 1 pass mekmitasdigoat netmask # ifconfig carp1 create # ifconfig carp1 vhid 2 pass mekmitasdigoat netmask The setup for host B is identical, but it has a higher advskew: # ifconfig carp0 create # ifconfig carp0 vhid 1 advskew 100 pass mekmitasdigoat netmask # ifconfig carp1 create # ifconfig carp1 vhid 2 advskew 100 pass mekmitasdigoat netmask Because of the preempt option, when one of the physical interfaces of host A fails, advskew is adjusted to 240 on all its carp interfaces. This will cause host B to preempt on both interfaces instead of just the failed one. In order to set up an ARP balanced virtual host, it is necessary to configure one virtual host for each physical host which would respond to ARP requests and thus handle the traffic. In the following example, two virtual hosts are configured on two hosts to provide balancing and failover for the IP address First the carp interfaces on Host A are configured. The advskew of 100 on the second virtual host means that its advertisements will be sent out slightly less frequently. # ifconfig carp0 create # ifconfig carp0 vhid 1 pass mekmitasdigoat netmask # ifconfig carp1 create # ifconfig carp1 vhid 2 advskew 100 pass mekmitasdigoat netmask The configuration for host B is identical, except the skew is on virtual host 1 rather than virtual host 2. # ifconfig carp0 create # ifconfig carp0 vhid 1 advskew 100 pass mekmitasdigoat netmask # ifconfig carp1 create # ifconfig carp1 vhid 2 pass mekmitasdigoat netmask Finally, the ARP balancing feature must be enabled on both hosts: # sysctl -w net.inet.carp.arpbalance=1 When the hosts receive an ARP request for, the source IP address of the request is used to compute which virtual host should answer the request. The host which is master of the selected virtual host will reply to the request, the other(s) will ignore it. This way, locally connected systems will receive different ARP replies and subsequent IP traffic will be balanced among the hosts. If one of the hosts fails, the other will take over the virtual MAC address, and begin answering ARP requests on its behalf. Note: ARP balancing only works on the local network segment. It cannot balance traffic that crosses a router, because the router itself will always be balanced to the same virtual host. SEE ALSO
netstat(1), sysctl(3), arp(4), arp(8), ifconfig(8), sysctl(8) HISTORY
The carp device first appeared in OpenBSD 3.5. BSD
October 16, 2003 BSD

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