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Dead Peer Detection - will remote PIX reconnect ?

Posted on 2003-11-09
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Last Modified: 2013-11-16
Hi all,

Well, time for me to ask a question. I've done the reasearch and can't find the answer anywhere and I don't yet have any practical experience in this situation (PIX failover).

I have a PIX 515 that is going to be upgraded to a pair of 515E's in a failover configuration. There are approximately 150 PIX 501's that each connect a VPN tunnel back to the 515 (this situation is a retail store chain, hence the large number of remote sites). I know that even with stateful failover, the IPSec information will not failover to the backup PIX 515E.

My question is, with Dead Peer Detection (isakmp keealives) will the remote 501's attempt to reconnect after they stop receiving a response to their keepalive packets ? I want the situation that if a failover occurs, then all of the store 501's will automatically attempt to reconnect again and so that when they do this, it will be to the standby PIX.
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Question by:td_miles
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by:lrmoore
ID: 9714828
You're in luck. In a failover pair, if the primary fails, the secondary takes on the complete identity of the primary. Therefore, there is only one external IP address for the remotes to connect to. The VPN tunnels will be preserved.
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by:td_miles
ID: 9718911
Can you point to any source of information that indicates that the VPN tunnels will be preserved ? All of the material I found says that the VPN tunnels are NOT replicated to the standby unit. The following is from IOS 6.2, so unless they changed it in 6.3, It isn't any different. EG:

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http://www.cisco.com/univercd/cc/td/doc/product/iaabu/pix/pix_62/config/failover.htm

What information is replicated to the standby PIX Firewall on Stateful Failover?
* The configuration.
* TCP connection table including timeout information of each connection.
* Translation (xlate) table.
* System up time; that is, the system clock is synchronized on both PIX Firewall units.

What information is not replicated to the standby PIX Firewall on Stateful Failover?
* The user authentication (uauth) table.
* The ISAKMP and IPSec SA table.
* The ARP table.
* Routing information.
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So the situation I would have after failover the 515E that was now active (the failover unit) would not have all of the VPN endpoints on it (ISAKMP & SA tables). The 501's would still think that it should, as the IP address would not have changed (part of failover). So the question still stands, will the 501's be able to automatically re-connect the tunnels (ie. they will need to sense that the 515E at the other end has dropped the tunnel and so then they can initiate it again).
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lrmoore earned 400 total points
ID: 9719115
I know I read somewhere that they were going to extend the stateful failover to the VPN, but I can't find the document.. it might be in 6.4 (to be released tbd). Even 6.3

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Stateful Failover—During normal operation, the active unit continually passes per-connection stateful information to the standby unit. After a failover occurs, the same connection information is available at the new active unit. Supported end-user applications are not required to reconnect to keep the same communication session.
The state information passed to the standby unit includes:

NAT translation table
TCP connection states
H.323, SIP, and MGCP UDP media connections
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What information is not replicated to the standby PIX Firewall on Stateful Failover?
The user authentication (uauth) table.
The ISAKMP and IPSec SA table.
The ARP table.
Routing information.
Other UDP connections.
----------------------------------
Even though the ISAKMP state is not maintained, the tunnel is re-created on the fly.
From experience, the VPN tunnel will automatically re-build itself almost instantly. I have several PIX failover pairs with permanent LAN-LAN VPN tunnels. I've never had a problem.
To test it out, simply power off the PIX, then power it back on. You broke the VPN connections, the state was certainly not maintained during power off, and the tunnels are rebuilt almost instantly. The same thing happens on a failover. It just works..
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by:td_miles
ID: 9719373
You're right, I hadn't thought of it like that. Unfortunately, I don't have a failover pair to try it on (yet), but I tried it on another VPN tunnel and it did come back up almost immediately once there was traffic over it (after a reload of the PIX at one end).

Just wanted to make sure before I say "yep, it will all be fine"
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by:lrmoore
ID: 9719404
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