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single ip address on multiple nics

Posted on 2004-11-02
Medium Priority
Last Modified: 2013-11-22
i have a case in which I need to have 1 single ip address on multiple nics in a FreeBSD server.
I want this for several purposes

1) Additional bandwidth to the serverusing existing network
2) To Maintain uptime in the network.
I want to have each card connected to a different switch, and then the switches linked to each other

          ***************+   BSD SERVER +****************
          *                            + ++++++++++++                              *
          *                                                                                     *
          *                                                                                     *
+++++++++++                                                                ++++++++++++
+  SWITCH    +---------------------------------------------------+      SWITCH  +
+++++++++++                                                                ++++++++++++

This is basically what I want. The resof of the network are also, connected to these switches.

If possible I would want to be able to get the aggregate of the interfaces to the switch.
Meaning if I have 4 nics in the BSD server, get 400mb/s :>
Like I said, if possible.

Please advise
Question by:Protorian
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Author Comment

ID: 12475642
I want that if a switch goes bad, or if an ethernet port on the server goes bad,
That service continues to be up.


Expert Comment

ID: 12477858
>> Additional bandwidth to the serverusing existing network

you can't have two nic's using the same ip address simultaneously.
The ip protocol stack will refuse to bind the ip to an nic if it is already
in use on some other nic. However it is possible to have the arrangement
where if a nic goes bad, you can have the other nic up on the same address.

hope this helps,


Author Comment

ID: 12479094
to the network, will it seem like the two cards have the same address?
And will that also aggregate the bandwidth?
Or is that something different?

If this is possible would you please give me the config.
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Accepted Solution

van_dy earned 256 total points
ID: 12487187
Consider just using 2 nics on your server for the moment.

like i said, you can't have two nic's to use the same ip address "simultaneously".
however, you can have separate ips for your 2 nics, and let the server listen on the
wild card address(you can accept the packets destined for nic2 even if they
arrive on nic1,  weak end system model). you will need to keep two entries in
your dns records for your server. as an example.

some.name.org        IN A     //some.name.org being the site name
                                IN A

Now i dont think connecting the switches as you are
doing is a very good solution. This is because you will
need to configure your switches for trunking. Plus in case
of a failure, the other nic would become the bottleneck. An easier
strategy is to use 2 more nics.

nic1 <--> nic3(redundant)
nic2 <--> nic4(redundant)

Now you can create a cron job, which periodically pings(say at intervals of 20 seconds)
both nic1 and nic2. if  nic1 fails, it assigns the ipconfig of nic1 to nic3, and similarily if nic2
fails, it assigns the ipconfig of nic2 to nic4.  
This way you can have the required redundancy along with additional bandwidth(not to
forget, but at a cost of 2 extra network cards).

hope this helps,

Assisted Solution

paranoidcookie earned 248 total points
ID: 12492004
You are wrong to say you cannot bind an ip address to two cards. 3com have been producing drivers to do this for years in order to provide higher reliablilty and speed. So the answer is you might be able to dual bind cards depends on the drivers available.

Assisted Solution

frankcheong earned 248 total points
ID: 12521196
check out /usr/ports/net/freevrrpd

/usr/ports/net/freevrrpd/pkg-descr reads:

freevrrpd is a VRRP (Virtual Router Redundancy Protocol) implementation
daemon under FreeBSD.  freevrrpd is part of the High UpTime project.
This daemon has been rewritten from scratch and is not based on
existing projects.  In this second public release, you can find:

       * A daemon RFC 2338 Compliant adapted on FreeBSD systems
       * Implementation of Virtual Adresses
       * Support for multiples VRID
       * Master announce state by sending multicast packets via BPF
       * Changing routes and IP in 3 seconds
       * Doing gratuitous ARP requests to clean the cache of all hosts
       * Election between different slave servers
       * Same host can be Slave and Master at the same time
       * Automatic Downgrade to Slave if a Master is up again
       * Anti-Address Conflict system
       * Multi-threaded vrrp daemon
       * Plain text password authentication
       * Using now only one BPF device for all VRID
       * Support netmask for Virtual IP addresses
       * Support for monitored circuit and dependances between VRIDs

WWW: http://www.b0l.org/?idcategory=3&idsection=1

Expert Comment

ID: 12521199
But anyway, all you achieve is high uptime but not double throughput.
LVL 62

Expert Comment

ID: 12536357
And you cannot have both speed and safety at once....
LVL 62

Assisted Solution

gheist earned 248 total points
ID: 12536377
ive just put two network adapters in a bridge on this FreeBSD system i work on, plgged another cable in other NIC, unplugged first and it kinda passed without any headache

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