Link Aggregation through transparent Cable Modems

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I have two cable modems which currently provide 1 Mbps of upstream each, and
I want to combine these two modems into 1 transparent fat pipe. Currently I
have two static IPs from my ISP on the same /24 subnet of which only 1 is
being in use, and each of the modems acts almost like a passive hub, in
which I can use the same static IP on a router connected to either modem.
That is, I can plug ModemA into fa0/0 and be able to ping default gateway,
and then swap ModemA with ModemB and still be able to ping default gateway.
A show arp command will show the same IP to MAC mapping for either modem,
thus these two modems are like passive transparent devices.

Example-->
(The following examples uses fake non internet routable IPs)

ISP Default Gateway IP: 172.16.128.1/24 00-c0-1b-2a-5f-2d
Router: 172.16.128.2/24 00-a0-1c-2d-3e-4f (FastEthernet 0/0)

Given this transparancy, I thought that it might be possible to send data
per-packet out to these modems, to achieve 2Mbps of upload to a SINGLE
destination, by having two interfaces acting as 1 logical interface, and
performing round robin PER-PACKET out those interfaces. That is, for
example, 172.16.128.2 can upload a file to 142.231.36.6 at 2Mbps.

Are there any way of achieving this? I have thought of Cisco
FastEtherchannel (Layer 2) or some other Layer 2 trunking protocol, Cisco
CEF doing per-packet, but no idea of they will work or not.


Any ideas greatly appreciated. It seems like there must be a way to
aggregate this bandwidth.



Re: Link Aggregation through transparent Cable Modems
I'm doubtful you can get this aggregation without the cooperation of your
ISP.  As far as I know, bundling requires specific configurations at each
end of the connection, I.e. the ISP needs to configure their router to
recognize the two streams from your cable modems as a single stream.

It has to be asked: I assume your ISP does not yet offer 2mbps service over
a single connection?  Or is this configuration for redundancy?

mjt

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Re: Link Aggregation through transparent Cable Modems
The ISP does not offer 2Mbps service yet. I have seen this working before
believe it or not, people using UNIX/Linux has done it through Channel
Bonding. In theory, I believe, it should work, at least for the upload
direction. My theory is that if you break up the stream and send it out each
modem, the TCP stack at the ISP's end will know how to reassemble the
packets. In terms of downstream, traffic, it will only go through one of the
modems (or both and thereby getting duplicates) because of the ARP
association. I have seen it working and the aggregation only works in the
UPSTREAM direction.

Is there a Cisco solution for doing this, such as CEF or Etherchannel, or
would I need to go fiddle around with UNIX?



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Re: Link Aggregation through transparent Cable Modems
On Sat, 21 Apr 2007 16:55:46 +0000, derSchweiz wrote:

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Yes you can do nic bonding on Linux/Unix and also on Windows with Intel
and Broadcom NICs. This is not going to help you with two Cable Modems
though.

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How is it going to work for the upload? The bonding will need to be done
on the Cable Modems, which more than likley your ISP is not going to
support or setup for you.

Re: Link Aggregation through transparent Cable Modems

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Some one has done this sucessfully without the help of the ISP using
netgraph module on FreeBSD but it only works in the upstream. One 2 many I
think it was called. Again the thing is, as mentioned earlier, the modems
are transparent so you can use the SAME IP address on BOTH modems. Now, if I
were to write a driver that round robins packets out to each of the modems,
in theory the head end would know how to reassemble the stream?

Take a look at this post:

http://www.dslreports.com/forum/remark,13826541


However I received news that Netgraph doesn't work any more (at least for
this ISP), so there must be another way of doing this.

I know for SURE that bonding at Layer 3 works by building tunnels to a
colocation provider with high bandwidth and running CEF per-packet, but im
looking for a more light-weight solution.

Thanks again.



Re: Link Aggregation through transparent Cable Modems
What router do you have? Is it Cisco? Then you can do it without your ISP
help. However it's not that easy and not that inexpensive.

If you have Cisco router with 3 Ethernet interfaces (you may have two,
however then you will require a switch with VLANs capability). Basically the
idea is that you should have 3 separate logical interfaces in your router.
One interface connects to your LAN or firewall), and two other interfaces
connect to two cable modems (either directly or through a switch). If you
have two equal cost routes to the host, your router will do "load-balancing"
between these two routes.

However there is another problem comes up - NAT translations. One modem
expects one IP address, and another expects another. So, you may get
asymmetric routing, when traffic is going one way, and response is coming
another. May be not a problem - may be a problem. So you may try to define
both "outside" interfaces as "ip nat outside". In most cases it will do NAT
when the packet hits the interface, and response will have correct IP
address as a destination.

Good luck,

Mike
CCNP, CCDP, CCSP, Cisco Voice, MCSE W2K, MCSE+I, Security+, etc.
CCIE R&S (in progress), CCIE Voice (in progress)
------
Headset Adapters for Cisco IP Phones
www.ciscoheadsetadapter.com
www.headsetadapter.com






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Re: Link Aggregation through transparent Cable Modems
If this does work, wouldn't the remote host out on the internet see the same
TCP session from 2 different source IPs (one from each of the cable modems),
and cause problems?


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Re: Link Aggregation through transparent Cable Modems
No. As I told, if packet takes one route, it's IP address will be translated
into one IP address, if it takes another - it will have another IP address.

Good luck,

Mike
CCNP, CCDP, CCSP, Cisco Voice, MCSE W2K, MCSE+I, Security+, etc.
CCIE R&S (in progress), CCIE Voice (in progress)
------
Headset Adapters for Cisco IP Phones
www.ciscoheadsetadapter.com
www.headsetadapter.com

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Re: Link Aggregation through transparent Cable Modems
Okay, I placed 2 "ip nat outside" on each of the interfaces with different
IPs, and did a NAT overload on both of them.

Now, when I ping from the router to my ISP's default gateway AFTER the ip
nat outside, only one of the gateways reply, I take out the ip nat outsides,
both the gateways reply.

I have a feeling that it may be using the same source address when going
out, and I know for sure my ISP does ingress filtering i.e. allow only
assigned IP address on each modem to go out.

Is there anything else I have to do like route maps to get the packets to be
translated into different IPs out each modem?

Basically this is what I have right now:

fa0/0
  ip address dhcp
  ip nat outside
!
fa0/1
  ip address dhcp
  ip nat outside
!
int serial0/0
  ip address 172.16.1.1 255.255.252.0
  ip nat inside
!

access-list 101 permit ip any any
access-list 102 permit ip any any

ip nat inside source list 101 interface fastEthernet 0/0 overload
ip nat inside source list 102 interface fastEthernet 0/1 overload

ip route 0.0.0.0 0.0.0.0 <gateway of fa0/0>
ip route 0.0.0.0 0.0.0.0 <gateway of fa0/1>

Thanks again!

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