S e n d d o c u m e n t a t i o n c o m m e n t s t o m d s f e e d b a c k - d o c @ c i s c o . c o m
35-20
Cisco MDS 9000 Family CLI Configuration Guide
OL-16184-01, Cisco MDS SAN-OS Release 3.x
Chapter 35 Configuring IPsec Network Security
Crypto IPv4-ACLs
Figure 35-6
IPsec Processing of Mirror Image Configuration
As
Figure 35-6
indicates, IPsec SAs can be established as expected whenever the two peers' crypto
IPv4-ACLs are mirror images of each other. However, an IPsec SA can be established only some of the
time when the IPv4-ACLs are not mirror images of each other. This can happen in the case when an entry
in one peer's IPv4-ACL is a subset of an entry in the other peer's IPv4-ACL, such as shown in cases 3
and 4 of
Figure 35-6
. IPsec SA establishment is critical to IPsec. Without SAs, IPsec does not work,
causing any packets matching the crypto IPv4-ACL criteria to be silently dropped instead of being
forwarded with IPsec security.
In case 4, an SA cannot be established because SAs are always requested according to the crypto
IPv4-ACLs at the initiating packet's end. In case 4, router N requests that all traffic between subnet X
and subnet Y be protected, but this is a superset of the specific flows permitted by the crypto IPv4-ACL
at switch M so the request is not permitted. Case 3 works because switch M's request is a subset of the
specific flows permitted by the crypto IPv4-ACL at router N.
Because of the complexities introduced when crypto IPv4-ACLs are not configured as mirror images at
peer IPsec devices, we strongly encourage you to use mirror image crypto IPv4-ACLs.
The any Keyword in Crypto IPv4-ACLs
Tip
We recommend that you configure mirror image crypto IPv4-ACLs for use by IPsec and that you avoid
using the
any
option.
The
any
keyword in a permit statement is discouraged when you have multicast traffic flowing through
the IPsec interface. This configuration can cause multicast traffic to fail.
Internet
S0
S1
Switch M
Router N
Mirror image
access lists at
Switch M S0
and
Router N S1
IPSec access list at S0
permits
Switch M Host B
permits
Host B Switch M
M B
or B M
SAs established for
Traffic M B (good
SAs established for
Traffic M B (good
SAs cannot be
established and
packets from Host
B to Switch M are
dropped (bad)
SAs established for
Traffic X Y (good
M B
B M
M B
or B M
or M C
permits
Switch M Host B
permits
Subnet X Subnet Y
permits
Subnet Y Subnet X
permits
Subnet Y Subnet X
IPSec access list at S1
1st packet
Result
Case 1
Case 2
Case 3
Case 4
Subnet X
Subnet Y
Host B
Host C
Содержание 9124 - Cisco MDS Fabric Switch
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