CEF LoadBalance on 2 ADSL connections

Answered Question
Nov 16th, 2009

Hi there, Can anyone help me with CEF load balance. I have 2 ADSL connections on the router 2811 and I am trying to load balance over these 2 links. Please see the attachment for my current configuration. The problem is I tried to browse the internet some website is not accessible and if it can access it take a long time to change from page to page. What is the problem here? I understand that the router see the 2 default route with the same cost and CEF will load balance the traffic using per-destination by default.. But the problem is exists.. Anyone has any idea what I did wrong..

Thanks in advance..

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Correct Answer by Paolo Bevilacqua about 7 years 1 month ago

All seems good, try configuring an host route so that the FTP server is reached using one interface only.

Correct Answer by Paolo Bevilacqua about 7 years 2 months ago

PPP header is 8 bytes. IP and TCP header togethers are 40. From that the simple math.

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Correct Answer by Paolo Bevilacqua about 7 years 2 months ago

Under both dialer interfaces:

ip mtu 1492

Under FastEthernet0/0:

ip tcp adjust-mss 1452

Optionally:

sub-interface are not needed with PPPoE

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Correct Answer
Paolo Bevilacqua Mon, 11/16/2009 - 12:52

Under both dialer interfaces:

ip mtu 1492

Under FastEthernet0/0:

ip tcp adjust-mss 1452

Optionally:

sub-interface are not needed with PPPoE

prachaya_k Thu, 11/19/2009 - 21:29

Great!! Woring perfectly...  Thank you very much.. Could you kindly explain how to calculate MTU on Dialer interface and ip tcp adjust-mss 1452 on Fa0/0. Or any link to document related to this problem will be really appretiated...

Correct Answer
Paolo Bevilacqua Fri, 11/20/2009 - 14:25

PPP header is 8 bytes. IP and TCP header togethers are 40. From that the simple math.

.

prachaya_k Fri, 11/20/2009 - 19:43

Thanks a lot p.bevilacqua , just a few more question on why do I need to recalculate this MTU, in what scenario that need to do this? I mean if I were to use other type of WAN connection e.g. ISDN VPN MPLS FramRelay, will I need to adjust these MTU? If it need to adjust MTU then it will always minus 40 bytes due to IP and TCP heade and plus addition MTU from WAN technology, is this correct?

Paolo Bevilacqua Sat, 11/21/2009 - 03:19

Each case is different, you have to test first.

The second commnd is the TCP MSS, not MTU. It is not always necessary, only when there are problems.

prachaya_k Tue, 11/24/2009 - 22:34

The same problem appear when user were trying to use FTP to FTP server on internet. Do you have any idea what could be the problem here? Internet web browsing is fine only FTP connection is a problem. What happen is some user able to log on and get file from FTP server while some user cannot log on at all. What else might be nessesary except from adding MTU 1492 on Dialer interface and ip tcp-mss 1452 on fa0/0.

Thanks.

Prachaya

Correct Answer
Paolo Bevilacqua Fri, 11/27/2009 - 08:59

All seems good, try configuring an host route so that the FTP server is reached using one interface only.

Junaid Abbas Wed, 12/02/2009 - 23:32

Hi,,

I also have 2 Internet Connections, both are DSL, I have Cisco 1811 router which has 2 WAN ports and 8 L2 Ports, I want to configure my both internet connections for load balancing as well want to connect soft VPN,

I viewed your configuration, you used dialer interfaces with ATM interface configured,,,

My question is .. why you configured ATM interface?

Can I use your configuration for this purpose?

Please Advise

Regards,

Junaid

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