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Per Hansen
*nix forums beginner
Joined: 04 Apr 2006
Posts: 1
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 Posted: Tue Apr 04, 2006 12:12 pm Post subject:
Can you do NLBS with layer 3 switches?
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Where I work we've got an Infinite Storage NAS. At the back of this are
two NAS heads which is the ethernet interface to the NAS. This consists
of 3 ports and there are 2 heads for redundancy.
We use NLBS to load balance between the 3 ports on the head. SGI are
saying that this does not officially work with layer 3 switches. In our
case, all 3 ports are connected to the same layer 3 switch. This works,
but the throughput lower than you would expect. We can't turn the layer
3 switching off as we need this for inter-vlan routing.
So I am stuck here...don't really understand why NLBS does not work
with layer 3 switches.
My question is though: is there another way we could do this to improve
throughput? |
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Bill Ryder
*nix forums beginner
Joined: 13 Apr 2006
Posts: 1
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| Posted: Thu Apr 13, 2006 11:13 pm Post subject:
Re: Can you do NLBS with layer 3 switches?
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On Tue, 04 Apr 2006 05:12:30 -0700, Per Hansen wrote:
| Quote: | So I am stuck here...don't really understand why NLBS does not work
with layer 3 switches.
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From here:
http://techpubs.sgi.com/library/tpl/cgi-bin/getdoc.cgi/srch14@nlbs%20operation/0650/bks/SGI_Admin/books/NLBS_AG/sgi_html/ch01.html
<quote>
Each client is given a MAC address to use for the IP address belonging to
the load-balancing device. The clients do not all have the same IP-to-MAC
address mapping; thus they send all of the packets they transmit to the
MAC address they were given without regard to connection.
</quote>
So that's the problem. Each client is given a different mac address for
the same IP address. Once you hit a layer three switch that MAC address is
not seen on the other side - the mac address of the layer three switch is
used. So any client on a different network will send the packet to the MAC
address of the L3 switch. The L3 switch will only remember one mac address
for a given ip address so it can't load balance on the way back.
The only balancing you can do across a layer 3 boundary from NLBS is
outbound unfortunately.
However - you should poke SGI. The more people who ask for layer 3 load
balancing the more likely it is they will implement it. It's not hard it
just requires time and money. They should really have done etherchannel
style load balancing or something similar. |
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