Routing problem on Cisco 837 to Microsoft, Ebay, Cisco...

[gareth60]

Hi all,

I'm by no means a IOS expert, hence this post.

I run a Cisco 837 (adsl) which i'm very pleased with and has been working fine for 2+ years.

A short while ago, I had a problem where I could not access Ebay, Microsoft and a few other sites, but others worked fine. After a lot of playing around, I found that something has changed out in the internet and to fix it, I had to remove the access lists for incoming traffic (I established this by the errors being logged on my syslog server).

This was fine for months, until 2 days ago, when the same problem occured. This is strange as I have not changed anything (honestly, i've been on holiday!) and I have no access lists.

Help, i'm really stuck...

Thanks

Gareth

[alfredshum]

use a dummy PC without any personal firewall and with an ADSL modem to test your line and see if you can access the problemetic sites. If you can't, that means it's the problem in ISP and you have nothing to do except giving complaints.

If you can, that means something's wrong in your router. Paste the config here and let us help you to troubleshoot the problem.

[gareth60]

Thanks, that's what I did last time. I borrowed a USB modem off a friend. I'm waiting for him to bring it in, but i'm sure it's not the ISP otherwise others would have started complaining.

When I get home, i'll post my config.

Kind regards

Gareth

[johansens]

Hi there,

Are you running PPPoE on this ADSL-link? Can you ping and telnet at port 80 on the sites? If so, your problem may be with the MTU size. Check here (this applies to any situation where you have a lower MTU on at any point between a client and a server):

http://www.ciscotaccc.com/iprout/showcase?case=K58233890

Here is a document regarding troubleshooting MTU in a ADSL w/PPPoE environment:

http://www.cisco.com/en/US/tech/tk175/tk15/technologies_tech_note09186a0080093bc7.shtml

A very quick 'fix' would be as follows:

On you inside interface, do this:

ip tcp adjust-mss 536

Then you are guaranteed the packets will get through, but you will maybe get a drop in performance. You could set the MSS to a higher value (the MSS is the MTU-IPheader-TCPheader, where the headers are ususally 20 bytes each). Try also starting the MSS at 1452 (as recommended in the last link I posted).

[pauruizperez]

It seems that your problem could be with the MTU (if the problem is surfing Internet.

This problem only occurs if you're connecting to the ADSL line with PPP (PPPoE or PPPoA... Dialing and PAP or CHAP, you know...)

If that is not the case, this response is of no use for you

If so, try this:

(conf-int)# ip tcp adjust-mss 1452

In the Dialer interface

This should solve your problem, I think there is no need to put it on the Ethernet interface too. But if it's not solved, would make no problem if you put it.

Good luck:

Pau

[gareth60]

All,

The MTU had crossed my mind. When I had the problem last time, my ISP told me to put the MTU to 1430.

I'll try changing this when I get home and i'll let you know.

Many, many thanks for all the replies.

Gareth