iDirect TCP traffic problem

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Apr 24^th, 2012 at 12:30am

Hi,

I have a customer who was using iDirect connectivity from our hub for quite a long time. All of a sudden from last month the iDirect modem started to have some issues.

The modem stays connected on the RF level, all the RF specs are good no warning or alarm on modem but the TCP traffic going through the modem stops...I have seen some UDP traffic going through but all the TCP traffic stops and the modem needs to get power cycled to restore the connectivity.

TCP acceleration was switched off and the issue happened again...the frequency of these hang ups is after every 3-4 days......I have captured some packets to analyze if the modem is under TCP sync flood attach but the TCP traffic passing through seems to be legitimate....

Can anyone suggest what other things needs to be checked....I am doubting on iDirect modem because only this device needs to be restarted to restore the connectivity.....what might be the issue here...??

Regards,
saiahmed

Apr 24^th, 2012 at 11:52am

Is anything connected to the backplane, other than the client? Good chance you may have something viral that is exhausting the iDirect CPU (due to tcp sessions, etc). What is baffling is that you say occasional UDP passes.

Suggest you check the CPU duty cycle (via CLI) the next time this condition manfests itself on the your system.

Apr 24^th, 2012 at 5:47pm

I have checked the CPU load and it was 22% at the moment when modem was not passing any TCP traffic...a lot of errors were also there on the ixp0 port..see below the port specs taken during the problem...

ixp1

RX Bytes: 1637744836 Packets: 9142598 Errors: 12603 Drops: 0

RX FIFO: 0 Frame: 12603 Compressed: 0 Multicast: 304096

One thing to add here...this modem is connected to a Passport switch and we can see FCS errors occuring on the switch port even during the modem's normal operation.....and at the time of hangup these errors can be seen on iDirect ixp0 port.....but during normal operation iDirect ixp0 port doesn't have any errors....only the passport switch shows few errors every minute or two.......any suggestions...

May 1^st, 2012 at 9:27am

I have come across this many times. it is because of so many NAT sessions opened. to solve it you need to disable DHCP and use an Static IP in the LAN interface of the modem.

login to the modem and run below command to see NAT sessions status

nat stats

May 4^th, 2012 at 7:48pm

Hi Zein,

I am already using a static IP on the modem so the problem is not related to NAT sessions. We are not doing NATing. The modem also has 0 NAT sessions.

We have sort of isolated the problem by changing the cable between the modem and the switch. So far, the modem is running fine since last week. We are not seeing any more FCS errors on the ethernet port so hopefully we have found the solution as initially unshielded cable was used. Let's see...how it goes...

Saiahmed

Email me:eric@satsig.net

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