Load balance 881 across 3x VDSL lines

[Anthony Owen]

Hi All,

I'm doing a new install for a remote customer. They wish to load balance across 3x new VDSL lines that are being installed. the line provider will supply their own routers on the end of each lines, so I don't have the issue of DSL to Ethernet conversion for presentation to the 881.

I'm looking at creating an SVI (VLAN10) for the three Fa interfaces to be used for the WAN side, but my question is;

How do I route/load balance across the three DSL Paths. would config)# ip route 0.0.0.0 0.0.0.0 VLAN10 alone do the trick?

Thank you in advance for your responses.

[Philip D'Ath]

This question is like asking three people for the quickest route to the far side of the city.  There are many correct answers.

A really easy way to balance out the users between the circuits is to configure the routers like they were standalone, and then enable GLBP between the three.

http://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ft_glbp.html

What GLBP does is alternate giving out the MAC address for the default gateway of the three routers.  So the first user ends up on router 1, the second user on router 2, the third user on router 3, the 4th user on router 1, etc.

A quick example, on the internal VLAN, where you want 192.168.1.254 to be the default gateway shared by all the routers.  Note the routers still need a normal IP address on them, and this must be unique still.

interface VLAN1
  glbp 1 ip 192.168.1.254
  glbp 1 load-balancing host-dependent

[Giuseppe Larosa · Accepted solution]

Hello Anthony,

>> the line provider will supply their own routers on the end of each lines, so I don't have the issue of DSL to Ethernet conversion for presentation to the 881.

Each DSL line will have a different internal private IP subnet to which the Cisco 881 should connect you cannot put the three Fast ethernet interfaces under the same L3 interface.

Supposing that the line provider routers perform the NAT on each VDSL line you need three L3 interfaces where each of them get the IP address from the appropriate ISP router via DHCP 

ip address dhcp

The better scenario would be if you know the internal IP addresses of each of the three line provider routers. In this case you should use three default static routes with IP next-hop the three ISP routers

ip route 0.0.0.0 0.0.0.0 DSL1-IP-next-hop

ip route 0.0.0.0 0.0.0.0 DSL2-IP-next-hop

ip route 0.0.0.0 0.0.0.0 DSL3-IP-next-hop

So you need three SVIs on the C881 one for each fastethernet.

Note: the line provider has to configure a different internal LAN IP subnet for each DSL line in order for this design to work.You may need to make agreements with the ISP to achieve this.

Hope to help

Giuseppe

[Anthony Owen]

Hi Giuseppe,

The service provider has provided a /29 and No NAT on their routers for me. So your recommendation will work perfectly here!

Also looking at running PRF to load balance across the three interfaces?

[Philip D'Ath]

So you have a /29 and each of the service providers routers consume one IP address from this /29?

If so, I support Giuseppe's answer, and have rated it accordingly (you'll only need one "outside" layer 3 interface, but three default routes).

[Philip D'Ath]

I think I have mis-understood.  Are you using three 881's, one for each VDSL circuit, or a single 881 with all three circuits plugged into it?

[Anthony Owen]

Hi Philip,

It's a single 881 hanging off of three VDSL Lines. I've commented on Giuseppe's post with an updated theory on the config to go with, but defiantly open to thoughts and feedback!