PIX Crypto Tunnel Selection

Unanswered Question
Dec 3rd, 2007

I'm troubleshooting a site-to-site VPN tunnel between our Cat 6506 w/ VPN module to peer's PIX-515. The peer's crypto config appears to be incorrect and has two tunnels built between it and our VPN module.

Example:

!

crypto map mymap 1 match address acl1

crypto map mymap 1 set peer 1.1.1.1

crypto map mymap 1 set transform-set myset

crypto map mymap 2 match address acl2

crypto map mymap 2 set peer 1.1.1.1

crypto map mymap 2 set transform-set myset

access-list acl1 permit ip 10.0.0.0 0.255.255.255 10.0.0.0 0.255.255.255

access-list acl2 permit ip 10.10.0.0 0.0.255.255 host 10.255.255.1

!

My question is how does the PIX determine which crypto peer (and subsequent SA) to send a packet to? In this example if a packet is sent from 10.10.1.1 to 10.255.255.1, does it match acl1 because it is sequentially higher than the next peer, or does it match acl2 because it is the longest-match for that packet?

I've tried looking through Cisco's website and documentation, but I cannot find the order of precedence for crypto tunnels and how packets are selected/sent.

Anyone here know?

I have this problem too.
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ccbootcamp Mon, 12/03/2007 - 13:23

If memory servers, I believe the lower map statement has priority. Therefore, everything going from 10.0.0.0 /8 to 10.0.0.0 /8 will be encrypted using the first mymap statement...however, both remote peers and transform sets are the same, so I'm not sure what you're trying to accomplish here.

-brad

www.ccbootcamp.com

(please rate the post if this helps!)

jbalchunas Mon, 12/03/2007 - 13:59

The second crypto map statement should not be configured and is being removed. That is the first thing we identified on the peer that needed to be changed. I know that over-lapping networks can cause SPI errors (which is something we are seeing on our end), hence the reason we're troubleshooting.

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