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Webcast-Catalyst9k
New Member

1841 with 2 ISP doing failover

My 1841 properly re-routes traffic from its primary internet interface to its secondary internet interface.

The failover happens smooth. My ISP-A is connected to fas0/0 and my ISP-B is connected to fas0/1

What concerns me perhaps is a piece of cake for you guys... when in the primary ISP, I can ping anything from my inside hosts, but when in the ISP-B, I am not able to ping. I get request timeouts.

Is there any way this can be allowed? web browsing is all good when in ISP-B mode, it is just this pinging stuff

I have attached the running config

thanks

4 REPLIES

Re: 1841 with 2 ISP doing failover

hi

Once you are shifting the traffic onto the backup ISP have you tried checking up the default route ? Also m wondering how you are able to browse when you arent able to ping ..several possible reasons are there which can block your icmp packets..

but still can you revert how you do the testing over there in the secondary ISP ?

also have you tried checking pinging the default gateway which may be your NAS ip over there when you are on with the secondary ISP..

regds

New Member

Re: 1841 with 2 ISP doing failover

The routes are all good. When ISP-A goes down, the 1841 re-routes traffic to ISP-B and like I said, all is well, only the ability to ping anything from the inside hosts to the outside.

There has to be a line within the running-config (attached) that is preventing pinging from the inside to the outside under interface 0/1 (the one for the ISP-B)

For example, what does that "ip virtual-reassembly" line means?

Again, all is well except unable to ping outside from fas0/1

please help

thanks

Re: 1841 with 2 ISP doing failover

Hi

AFAIK its being used to overcome the attacks using incomplete ip fragments..

do refer this for more info ..

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124tcr/tsec_r/sec_i2ht.htm#wp1198845

regds

New Member

Re: 1841 with 2 ISP doing failover

Will this protection for attacks prevent pinging?

I went ahead and disabled it and now I am able to ping. Very funny, but I still would like to know more about this

thanks

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