Multiple ADSL Links load balanced

Answered Question
Oct 17th, 2008
User Badges:

Hello,


I am setting up a condo with a Cisco 3640 and a 200 port DSLAM. Currently it would take 6 months to get a fiber link to the building (no fiber in the area). We would like to get the place up and running fast and opted to install multiple ADSL lines. We will be offering VoIP services too for all 200 tenants.


The Cisco 3640 will be configured as a PPPoE Concentrator. It will dial out via multiple PPPoE ADSL lines.


The questions I would like to know are:

- How would I be able to load balance the traffic over multiple ADSL links in both directions without using NAT.

- Forward Voice traffic over another specific set of ADSL Lines load balanced as well.


We will be temporarily using the inexpensive technology until the fiber is put in place.


Thanks for any replies.

Correct Answer by Giuseppe Larosa about 8 years 9 months ago

Hello Rudy,

if you have a LAN switch you can use VLAN subifs on the router via a trunk port to connect to external ADSL routers/modems each of them is placed in a different Vlan.

But you cannot have pppoe client on each subif and what is very important you cannot use ip addresses in the same IP subnets on different LAN/Vlan subifs or ifs

So the ADSL devices have to be routers and different IP subnets have to be used.


In this case you can configure default routes with next-hops the ADSL routers lan interfaces.


To use a routing protocol is possible if you can configure the ADSL routers.


Hope to help

Giuseppe


  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 4.3 (3 ratings)
Loading.
Giuseppe Larosa Sat, 10/18/2008 - 02:07
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

Hello Rudy,


>> How would I be able to load balance the traffic over multiple ADSL links in both directions without using NAT.


using default static routes using as exit interface the different dialer X or virtual-template X


ip route 0.0.0.0 0.0.0.0 dialer1

ip route 0.0.0.0 0.0.0.0 dialer2

ip route 0.0.0.0 0.0.0.0 dialer3


>> Forward Voice traffic over another specific set of ADSL Lines load balanced as well.


using specific static routes for the VoIP destinations : suppose VoIP uses 172.16.4.0/22


ip route 172.16.4.0 255.255.252.0 Dialer4

ip route 172.16.4.0 255.255.252.0 Dialer5

ip route 172.16.4.0 255.255.252.0 Dialer6


if there is not a separate block of ip addresses for VoIP you could think to use PBR (policy-based routing )


Notice: I would not expect to be able to use more then 4 DSL lines for each destination and then there is also the limit on the C3640 chassis



Hope to help

Giuseppe


cyberglobe Sat, 10/18/2008 - 11:52
User Badges:

Hello Giuseppe,


I have done this in the past but if one of the dialers have gone down, then traffic gets blocked up as the dialer tries to get back online. Not sure if this has been fixed in 12.4 IOS.


What routing protocol can I use other than static route to make sure that the 3640 is aware of the connections staying up or down.


Also, is there a way I could do this over one Fast Ethernet Interface?


-Configure fa0/0 with no IP Address

-configure Fa0/0.1 for VLAN 1 IP 10.0.0.12

-... repeat

-configure Fa0/0.3 for VLAN 8 IP 10.0.0.82

-configure VLAN 1 dsl modem with IP 10.0.0.11

-... repeat

-configure VLAN 8 dsl modem with IP 10.0.0.81

-use a Layer 2-3 switch with port based VLAN routing since connected modems don't support VLAN.


Would this work? I know that there are limited ports available on the 3640 and therefore I am looking at alternative possibilities to help resolve this situation.

Correct Answer
Giuseppe Larosa Sat, 10/18/2008 - 12:10
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

Hello Rudy,

if you have a LAN switch you can use VLAN subifs on the router via a trunk port to connect to external ADSL routers/modems each of them is placed in a different Vlan.

But you cannot have pppoe client on each subif and what is very important you cannot use ip addresses in the same IP subnets on different LAN/Vlan subifs or ifs

So the ADSL devices have to be routers and different IP subnets have to be used.


In this case you can configure default routes with next-hops the ADSL routers lan interfaces.


To use a routing protocol is possible if you can configure the ADSL routers.


Hope to help

Giuseppe


cyberglobe Sat, 10/18/2008 - 13:40
User Badges:

Ok the IP address does not matter for the ADSL modems and the VLAN IP Addresses

I could number them as 10.0.1.0 - 10.0.8.0


This is what I would ideally like to do.

eg:

adsl#1 10.0.1.1 <-> VLAN #1 Port 1 +

adsl#2 10.0.2.1 <-> VLAN #2 Port 2 +

adsl#3 10.0.3.1 <-> VLAN #3 Port 3 +

adsl#4 10.0.4.1 <-> VLAN #4 Port 4 +

adsl#5 10.0.5.1 <-> VLAN #5 Port 5 +

adsl#6 10.0.6.1 <-> VLAN #6 Port 6 +

adsl#7 10.0.7.1 <-> VLAN #7 Port 7 +

adsl#8 10.0.8.1 <-> VLAN #8 Port 8 +

________________VLAN Port____|

______________based switch___|

_______________________Port 9|

Cisco 3640 FastEthernet 0/0 +------+

Fa0/0.1 VLAN #1 10.0.1.2 + Dialer1

Fa0/0.2 VLAN #2 10.0.2.2 + Dialer2

Fa0/0.3 VLAN #3 10.0.3.2 + Dialer3

Fa0/0.4 VLAN #4 10.0.4.2 + Dialer4

Fa0/0.5 VLAN #5 10.0.5.2 + Dialer5

Fa0/0.6 VLAN #6 10.0.6.2 + Dialer6

Fa0/0.7 VLAN #7 10.0.7.2 + Dialer7

Fa0/0.8 VLAN #8 10.0.8.2 + Dialer8


Anyways I tried setting up something on a test router but it seems like I only can setup "encapsulation dot1Q or isl"

Could I not configure isl to forward to a switch and the switch will dump the traffic onto the necessary vlan port?


Thanks in advance and hope the brain picking is not too painful ;)

cyberglobe Sat, 10/18/2008 - 14:43
User Badges:

reading up further about ISL, it seems like it is exactly what I am looking for as it is an Interswitch tagging and that devices like ADSL modems does not need to transmit vlan ids since the switch converts it at the port level.


Here is a quote from wikipedia's Virtual LAN page:

"With ISL, an Ethernet frame is encapsulated with a header that transports VLAN IDs between switches and routers. ISL does add overhead to the packet as a 26-byte header containing a 10-bit VLAN ID. In addition, a 4-byte CRC is appended to the end of each frame. This CRC is in addition to any frame checking that the Ethernet frame requires. The fields in an ISL header identify the frame as belonging to a particular VLAN.


A VLAN ID is added only if the frame is forwarded out a port configured as a trunk link. If the frame is to be forwarded out a port configured as an access link, the ISL encapsulation is removed."


Let me know if I hit the Jackpot or not...



Giuseppe Larosa Sun, 10/19/2008 - 02:21
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

Hello Rudy,

the Vlan tagging part will work unfortunately the pppoe-client feature works only on physical interfaces (at least it was so when I tested it on C3725 and C3745 and C7200 ).


However it is possible to link multiple dialers to the same physical interface:


you can use the proposed setup with:

router port and ADSL modem ports all in the same Vlan with no trunking


on router lan interface


int Fa0/0

mtu 1492

! multiple pppoe-client commands


But this is something you tried I suppose


There is a useful feature that allows to use object tracking with static routes and could help in your scenario to check what dialers are operational:


http://www.cisco.com/en/US/docs/ios/12_3/12_3x/12_3xe/feature/guide/dbackupx.html


the idea is to track the reachability of NAS ip address on each pppoe session.



Hope to help

Giuseppe


cyberglobe Sun, 10/19/2008 - 06:13
User Badges:

Damn, the subinterface can't be configured for pppoe-client access :(...


Who do I have to email to see if we can get this added to the IOS? It can be a solution that would work if the IOS had allowed it on a subinterface.




cyberglobe Sun, 10/19/2008 - 06:25
User Badges:

"However it is possible to link multiple dialers to the same physical interface:


you can use the proposed setup with:

router port and ADSL modem ports all in the same Vlan with no trunking "


Hi Guiseppe, The problem doing this way is that all traffic will now be going through each ADSL Modem and you end up having a broadcast storm or you end up having 8 tunnels going through 1 modem.


The object tracking looks interesting and I am going to read up on it tonight.


However, I would like to see IOS support Subinterface PPPoE clients so that I can create my ISL VLANs. This could allow people with no fiber in the area to be able to create huge networks over small unreliable links. This would ideally reduce the hardware necessary for the network and can also allow us to have up to 2-3 network modules as redundancy (if 1-2 modules being used for redundancy for the LAN).


This way we would not be limited to 10 ADSL Lines with NM-1FE2W cards and WIC-1ADSL (if they work with the 3640, I tried but it never booted).

cyberglobe Mon, 10/20/2008 - 19:26
User Badges:

Hello Giuseppe,


I was told that the pppoe-client can work in a subinterface with the 12.4(20)T or greater code. Have you tried to see if it actually works? I currently do not have access to IOS and therefore can't get it myself. Need to renew my TACs contract to be able to get it.


"You have to upgrade IOS to version 12.4(20)T or above for support command on subinterface. "


If that is the case, I could then do everything off of one Network Interface and will be able to handle at least 16 ADSL modems per FE NM port.

Giuseppe Larosa Tue, 10/21/2008 - 03:17
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

Hello Rudy,

12.4(20)T is really new and I haven't had a chance to test pppoe-client over a Vlan-subif but it is reasonable it can work: the vlan tag can provide a way to pass frames to the right subif and then the pppoe frame is processed.

It is a natural extension for pppoe client feature.

And you need to renew the service contract as well.


I don't know how many parallel paths you can support on modern IOS: once it was up to 6 then increased to 8, not sure 16 parallel paths are available for your router I think it is true for IOS XR on GSR and CRS.


Best Regards

Giuseppe



ABEDHAMZAS Sun, 10/19/2008 - 02:43
User Badges:

i'm thinking the best way to set this up is to use a DMZ style setup where machines that have public IPs are on a separate network/VLAN. And then connecting the routers together.

Actions

This Discussion