ADSL link load balancing on 2821 router

Answered Question
Jun 28th, 2008

One of our customer having Cisco 2821 router where three ADSL line had terminated on 3 separate ATM interface on same router. Customer wants to do the following configuration -

1) They want to do the link aggregation for all 3 ADSL link, terminated on same router

2) They want to do the load balancing for all 3 ADSL link, terminated on same router based on per packet or per session.

Please suggest me the configuration how to do that.



I have this problem too.
0 votes
Correct Answer by Paolo Bevilacqua about 8 years 6 months ago

It is the link in my first post above. Will distribute traffic in a statistical equal amount.

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Overall Rating: 5 (3 ratings)
manojdubey02 Sat, 06/28/2008 - 05:06

Customer having three ADSL line from same ISP.

This link is useful to configure load balancing between these three ADSL link ...or there is any other way to configure

Paolo Bevilacqua Sat, 06/28/2008 - 05:19

Unless you can take special agreements with the ISP, there is no other way than NAT load balancing as indicated above.

jamesl0112 Sun, 06/29/2008 - 00:40


Thanks for posting that informative link!

Looking at the sample configuration provided:

ip route dialer 0 track 123


ip nat inside source route-map fixed-nat interface Dialer0 overload

ip nat inside source route-map dhcp-nat interface FastEthernet0 overload


access-list 110 permit ip any


route-map fixed-nat permit 10

match ip address 110

match interface Dialer0


route-map dhcp-nat permit 10

match ip address 110

match interface FastEthernet0

1. Why doesn't the default route of 'ip route dialer 0' override any load-balancing and send everything through the dialer interface?

2. If you wanted to force specific traffic through a certain connection (e.g. IPSec or VOIP) would the correct way of doing this be to put these in an access list and have a different access list being matched by each route-map?


Paolo Bevilacqua Sun, 06/29/2008 - 02:39

1. the example doesn't actually load balance. You need as many default routes as many interfaces you have.

2. Most often, normal routing is enough. e.g you need ipsec or voip traffic ito go to a given IP address, just use a specific route for that.

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jamesl0112 Sun, 06/29/2008 - 03:47

Wouldn't the two NAT statements with route maps specifying both outside interfaces make it load-balance?

Paolo Bevilacqua Sun, 06/29/2008 - 04:13

No. NAT statements define what traffic is natted and on which interface.

Initial outgoing traffic is driven by routing statements anyway.

Paolo Bevilacqua Sun, 06/29/2008 - 09:02

I just found two more errors in the referenced document.

1st, under dialer, there is "ip tcp- mss-adjust" that beside being invalid without a parameter, is not needed under dialer.

2nd, the only default route present, as a track statement that is not referenced elsewhere.

I've notified cisco of these and hope theu can have it corrected sometime

manojdubey02 Mon, 06/30/2008 - 20:19

Outgoing bandwidth aggregation is offered at the TCP/UDP session layer. The user defines weights for the WAN links based on the bandwidth of the link. When a session is

generated from the LAN the router computes which link has the most available

bandwidth and routes traffic from that session over that particular WAN link. The router allows selection of 2 load balancing algorithms: (1) symmetrical round robin or (2)

intelligent (weighted) load balancing. The symmetrical round robin will route sessions to

3 all links in a round robin manner. The intelligent load balancing will compute a ratio between the weight (bandwidth capacity) of the different lines and route sessions

accordingly. That is, the faster the link the more sessions that will be sent over that link to make the most efficient use of all the bandwidth available.

Please suggest me these two method is possible to configure (Cisco 2821) for Outgoing bandwidth aggregation below -

The router allows selection of 2 load balancing algorithms:

(1) symmetrical round robin or

(2) intelligent (weighted) load balancing.

Paolo Bevilacqua Tue, 07/01/2008 - 02:46

Form where exactly you took the excerpt above ?

It seems like it is OER ,that it would not be my recommendation.

Initially you should use only the simplest algorithm, that is CEF.

Then if it not satisfying you can look into alternatives.

manojdubey02 Tue, 07/01/2008 - 03:01

Please suggest me tha Algorithm (CEF), I need to sort the above problem.

I don't have any idea about CEF. please can you help me to do the configuration...



Paolo Bevilacqua Tue, 07/01/2008 - 03:10

CEF is the default, so just configure as per document linked above, and you will be OK.

manojdubey02 Tue, 07/01/2008 - 03:54

Please send me the configuration link by using CEF. Please confirm me whether it will distribute traffic between two ADSL link in equal amount.



Correct Answer
Paolo Bevilacqua Tue, 07/01/2008 - 03:57

It is the link in my first post above. Will distribute traffic in a statistical equal amount.


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