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Community Member

ATM problems with 1802 vs. 826


I am experiencing some strange behaviour: I had a 826 router on an ADSL circuit running Internet access and VPN. The download speed of unencrypted Internet traffic is as expected. Over the time the crypto performance of the 826 did not meet my requirements anymore, so I replaced it with an 1802 to gain crypto performance.

I configured both routers basically the same and it works.

But: The performance of the 1802 downloading even clear text traffic is very bad. I get about 1Mbit/s when using the 826 but never more than 100Kbit/s with the 1802.

I already replaced the 1802 with a different model (so it is not a HW problem) and there are no obvious errors at the ATM interface or in the log.

This is the ATM part of the config, same on both:

interface ATM0

no ip address

ip tcp adjust-mss 1452

no atm ilmi-keepalive

dsl operating-mode auto

hold-queue 224 in


interface ATM0.1 point-to-point

ip address X.X.X.X

ip access-group 101 in

ip access-group 102 out

ip nat outside

ip inspect internet-out out

pvc 8/32

encapsulation aal5snap


crypto map vpn

The differences in the rest of the config are only device dependent.

Does anybody know about SW issues causing this?




Re: ATM problems with 1802 vs. 826


have you already analysed/compared the configs on both the devices ??

Is it possible to post out the relevant configs of both the device out here ?

also can you revert us whats the speed monitoring mechnaism being used and how you get the downloading speed details with both the devics ..


Community Member

Re: ATM problems with 1802 vs. 826


I created the 1802 config out of the 826. There are some differences e.g. ospf (which the 826 did not support). As well the original 826 just had one tunnel and for the 1802 I added two more tunnels for debugging purposes.

Find both complete configs attached.

Regarding performance measurement I first copied a large file back and forth over the VPN tunnel. I expected the 1802 beeing a lot faster, but it was even slower than the 826. After that I configured NAT and tried direct downloads from the internet and monitored the ATM interface. It is very obvious that the 1802 interface does not see more than about 150kbit/s. The 826 gets 1,5Mbit.

Before that I issued a call with the ISP (Telefonica) and they came on site with there own router (an 800 as well) and tested performance without any problems.

Btw. the IOS on the 1802 is

C180X Software (C180X-ADVIPSERVICESK9-M), Version 12.3(8)YI

the 826 is

C820 Software (C820-K9OSY6-M), Version 12.2(4)YA3

I searched already for bugs at CCO, but this is very confusing.



Community Member

Re: ATM problems with 1802 vs. 826

I upgraded now to 12.3(14)YT1 and the problem is gone...

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