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Advice on curing FRAG_TABLE_OVERFLOW errors

Hi all, I need some advice on the above error that I am recieving on my Cisco 877 router.

I can see that at the moment the fragment table threshold is 16.

I have my ADSL router in Bridged IP mode as that is how my ISP required it be setup.

I have noticed that the MTU on the ATM interface is 4470 bytes. Is this normal? The MTU on my BVI1 interface is 1500 bytes. Am i understanding right that at the moment the packets entering the ATM interface destined for the BVI1 interface will need to be fragmented because the MTU on the ATM interface is so large?

I have read a couple of forum posts and I think one answer is to increase the threshold level of the fragment table on my BVI1 interface to 64. Another is to reduce the MTU size of the BVI1 interface.

I understand the first resolution, but not quite sure how reducing the MTU size on the BVI1 interface will have a positive effect.

Just to confirm, the fragment overflow error that I am recieving is happening on the BVI1 interface.

Any advise on this would be very greatful.

Thanks

Mario

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New Member

Advice on curing FRAG_TABLE_OVERFLOW errors

OK,

i have increased the fragment threshold to 64... but the message is still appearing.

Without sniffing the traffic on the wire, can you suggest any alternate IOS commands that could help me?

I have lowered the MTU on the interface BVI1 to 1420 and I have configured the ip tcp adjust-mss to 1400

We have a host on the BVI1 interface sending a constant stream of traffic at around 350kbps to a host on the Internet (ATM0). Shouldnt the two hosts negotiate the maximum segment size to prevent all this fragmenting?

Could a firewall be blocking this from working perhaps?

Thanks

Mario

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